Collaboration Portraits

In conversation with Ana Henriques Correia, a key player in the development of the ATLAS Calorimeter

Edite Prado Felgueiras — Tue, 30 Jan 2024 08:25:03 +0000

In conversation with Ana Henriques Correia, a key player in the development of the ATLAS Calorimeter

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Edite Prado Felgueiras Tue, 30/01/2024 - 09:25

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tile calorimeter

Ana Henriques arrived at CERN in 1988 as a summer student, and never wanted to leave. She assumed the roles of technical coordinator and project leader of the ATLAS Tile Calorimeter, being involved in its design, construction, and installation processes. Later, she took the lead on the High Granularity Timing Detector (HGTD) project, while also being in charge of the hadronic calorimeter concept development for the Future Circular Hadron Collider (FCC-hh). Currently, she is the resources coordinator for the HGTD.

Ana Henriques Correia with a prototype of the High Granularity Timing Detector (HGTD). (Image: M. Cavazza/CERN)

My career in physics began at the University of Lisbon, but scientific curiosity has been with me since my early years in Castelo Branco, my hometown 300 kilometres from Lisbon. I might be one of the best examples of how a good high school experience can motivate students towards science. My physics teacher was outstanding – she challenged us to look beyond the obvious, to be ambitious, to be curious. And this was the trigger that led me to physics, which led me to the University of Lisbon, and then to the Laboratory of Instrumentation and Experimental Particle Physics (LIP), and, ultimately, to ATLAS.

In the early 1980s, Amélia Maio, my professor at the University of Lisbon started working with Peter Sonderegger, researcher at CERN, to develop the Spaghetti Calorimeter (SPACAL), a sampling calorimeter with scintillating fibres inserted into the absorber material. She was looking for students and I had the opportunity to join her team at LIP. I arrived at CERN in 1988 as a summer student to work on my diploma thesis on the radiation of scintillating fibres for SPACAL. The project was led by Richard Wigmans, one of the leading experts on calorimetric particle detection, and he invited me to come back the year after to do my PhD. SPACAL was being designed from the ground up and I was given the chance to be part of it. It was a dream opportunity for a young physicist.

A three-way race for the best calorimeter

SPACAL was part of a much broader initiative to develop detectors for the Large Hadron Collider (LHC) experiments. There were three hadron calorimeter concepts being studied: SPACAL was the RD1 Collaboration; the RD3 Collaboration was developing a full liquid-argon calorimeter; and the RD34 Collaboration was working on a scintillator tile sampling hadron calorimeter with a longitudinal tile configuration.

It was a very interesting and challenging period because we were designing everything from scratch. There was no playbook to follow.

Our goal with RD1 was to build a sub-detector that could measure particle jets with the best possible resolution. While RD1 did have excellent resolution, it didn't have longitudinal segmentation – a feature of RD34. The latter, with its iron structure and scintillator tiles read by optical fibres, also guaranteed reasonable construction costs. When the RD34 concept was selected as the best project – now simply known as the ATLAS Tile Calorimeter – I transitioned fully to its team, became a CERN fellow, and shortly after, became the Test Beam Coordinator.

1999: Ana in front of the ATLAS Tile Calorimeter barrel modules while they are being instrumented. (Image: ATLAS Collaboration)

Later, I was designated Assembly Coordinator and then Technical Coordinator of the ATLAS Tile Calorimeter. So, I really ended up being involved and following the whole process, from design and prototyping to installation and operations. It was a very interesting and challenging period because we were designing everything from scratch. There was no playbook to follow and we had several open questions about how the detector would perform. Testing the Tile Calorimeter's performance with beams and using simulations became crucial in guiding us towards refining the concept's maturity. In the end, it was truly impressive to witness how well it performed in collision data. It is an excellent detector that contributes to our superior calorimeter-only jet resolution.

The future of ATLAS

One of the greatest privileges of my professional career was being involved in the early stages of several projects. When I finished my time as Tile Project Leader in 2013, Kevin Einsweiler invited me to co-coordinate a task force – Large Eta Task Force (LETF) – to explore various scenarios for improving ATLAS’ end-cap and forward detectors for the High-Luminosity Large Hadron Collider (HL-LHC).

This presented a unique challenge, as instead of developing detectors for a project under construction, we were considering the future of an ongoing experiment. Not all of the ideas we collected made it into the final HL-LHC detector design, but it was an endeavour that led us to the design of ATLAS’ new Inner Tracking (ITk) Detector and to the development of the High-Granularity Timing Detector (HGTD).

2004: Ana posing with her team during the ATLAS Calorimeter assembly in the ATLAS Cavern. (Image: P.Loïez and M.Brice/CERN)

The HGTD was a wholly new concept in particle detector design, and required five years just to reach the approval stage. We were exploring extensions to the detector’s magnetic field coverage, improving how we could track muons. Honestly, it was extremely demanding for me as the HGTD Team Leader: we had to form a collaboration, deal with the joining and leaving of institutes, work on the detector concept, keep the team motivated and focused, and, in the end, get the project approved by ATLAS and the Large Hadron Collider Committee (LHCC). At the same time, I was coordinating the hadronic calorimeter concept development for the Future Circular Hadron Collider (FCC-hh) and editing the ATLAS Public notes summarising the LETF.

But the hard work paid off, and now we are entering into the construction phase. We have a collaboration that brings together more than 20 countries and a very aggressive work plan. We developed a detector that can adapt to changes in the HL-LHC schedule, giving us the possibility to work on its installation not only during the upcoming long shutdown of LHC (LS3) but also during shorter technical stops.

In retrospect, this was a very challenging and stressful period, but it left me with the feeling of a mission accomplished. So, in 2020, with the FCC-hh already on paper and the HGTD project underway, I moved to the HGTD resources coordination.

The challenges of leadership

If we look closely, we see that, perhaps, only 10% of the ATLAS Collaboration is based at CERN. Working in a global collaboration of scientists, engineers and technicians requires additional coordination skills to get all the puzzle pieces together for each project. I have always been part of coordination activities, and I like that. But, at the same time, it is an enormous challenge because projects are becoming increasingly long term, and team members end up not following the whole process. Ensuring a smooth transition between the people who arrive and those who leave is one of the biggest responsibilities I assume, at the risk of jeopardising the project.

Being part of a small workforce, like HGTD, within a large collaboration is an incredible opportunity that I hope my younger colleagues will take advantage of.

I can't say it has always been easy. Dealing with such demanding work can be tough, particularly when you have small children. There were times when I would meet my husband at CERN’s cafeteria to swap the kids for “shifts”. But, if I had to go back, I would do everything the same way. Having experience in both analysis and hardware turned out to be a boon for my career. Physics is an area in which you must be versatile.

If you want to succeed in physics nowadays, you have to be good at doing data analysis and you have to be good at working with software and hardware. You really have to be proactive and you cannot be afraid of taking risks. Being part of a small workforce, like HGTD, within a large collaboration is an incredible opportunity that I hope my younger colleagues will take advantage of. I've been lucky enough to see the ATLAS Tile Calorimeter through every stage of its development. Now my hope is that others will experience the same.

ATLAS Portraits is a series of interviews presenting collaborators whose contributions have helped shape the ATLAS experiment. Discover more ATLAS Portraits here.

In conversation with Kevin Einsweiler, an instrumental voice in ATLAS upgrades

Katarina Anthony — Mon, 06 Mar 2023 15:00:30 +0000

In conversation with Kevin Einsweiler, an instrumental voice in ATLAS upgrades

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Katarina Anthony Mon, 06/03/2023 - 16:00

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Kevin Einsweiler is a senior scientist at Lawrence Berkeley National Lab (LBNL). He joined the ATLAS Collaboration in 1993, playing an instrumental role in bringing US institutes into the LHC programme. He served as ATLAS Pixel Project Leader (2005-2009), Physics Coordinator (2011-2013) and Upgrade Coordinator (2014-2019). In this interview, Kevin shares how he became a particle physicist, discusses the formation of the LHC collaborations, and looks ahead to the next era of the ATLAS experiment

Portrait of Kevin Einsweiler. (Image: E. Ward/ATLAS Collaboration)

What sparked your first interest in physics? Was there a particular event or inspiring teacher?

I suppose my physics "origin story" is a little different, because it started in a car instead of a classroom. Because of a late birthday and a skipped year, I started university at 16 and lived at my parent’s home as an undergraduate. This meant that, every day, I would get a ride to the university with a neighbour (and father of my best friend) who was a physics professor. His name was Hans Courant and he led an incredibly interesting life; he came from a very prolific family of physicists and had worked on the Manhattan Project and at CERN. We would spend the drives having these fascinating conversations about particle physics. One day, during my second year in university, he invited me to visit Argonne National Lab to see an experiment he was working on (this was summer 1975). It was a small fixed-target experiment using polarised protons. This was not an experiment out of a textbook, but I got to wire-wrap some of the data acquisition (DAQ) system and write PDP assembly language programs. I was completely hooked.

He sounds like an incredible influence. How did this initial interest transition into a PhD in experimental physics?

It wasn’t immediate. I knew I was fascinated by physics and wanted to study it, but my undergraduate studies originally pushed me towards wanting to be a theorist. I think that’s pretty common for students: you spend all of your time learning concepts and solving simple physics problems, and end up imagining that could be a career.

While I really loved the mathematics behind quantum mechanics – and still find it incredibly beautiful – I also knew I loved building stuff. Perhaps it runs in the family: my grandfather was a construction contractor, my father and brother are urban planners. There was always work going on at home that I, even at a young age, loved getting involved in. Even so, it took me a while to reconcile that the hands-on side of physics was what I enjoyed most.

Luckily, I had this realisation before picking a graduate school. I decided on Stanford for my Ph.D, specifically because they had an accelerator and were launching new experiments. That gave me a chance to get in on an experiment on the ground level – designing, prototyping, building, operating and then doing my thesis on the data.

UA2 was really a great experiment and you can still see the influence it had on ATLAS today. Not just in the detector design, but also in establishing our community. It was where a lot of ATLAS people started their careers and we got used to its very congenial environment.

That’s something a lot of ATLAS people haven’t experienced – seeing an experiment through from start to finish.

That's right. It’s a multi-decade process now and involves hundreds, if not thousands, of people. My thesis experiment (SPEAR Mark III) had maybe 30 people on it, and only a half a dozen institutes. So I was able to work on a huge range of things – working with multiple kinds of electronics, writing the data acquisition system, and developing tracking chambers and calorimeters. It was really exciting and a great environment to start off in.

After graduating in 1984, you came to CERN to join the UA2 experiment on CERN’s Super Proton Synchrotron (SPS). How did that come about and how did you then transition into the proto-collaborations for the LHC?

There was a funny sort of a pipeline between SLAC and UA2 in those days – and part of that pipeline was Peter Jenni [UA2 physicist who went on to be the first ATLAS spokesperson]. I got to know Peter in 1979, when he was at SLAC working on the Mark II experiment. He was a more senior physicist, and I was a young graduate student. The Mark II collaboration had many strong physicists and engineers, several of whom were people I considered as mentors. That group had a lot of connections to the UA2 team and it was common knowledge that if you wanted to become an expert in instrumentation, you absolutely had to go to CERN and work on UA2. So that’s what many of us did.

UA2 was really a great experiment and you can still see the influence it had on ATLAS today. Not just in the detector design, but also in establishing our community. It was where a lot of ATLAS people started their careers and we got used to its very congenial environment. There were never any barriers between young people and senior people – a lot of great physicists, but no major egos. We all ended up forming close personal and professional relationships.

These ties carried over to the first LHC proto-collaborations. When you have a group of people with a proven track record of working well together, of course you want to build your collaboration around them. I also think there was a desire to carry forward the structure and spirit we’d fostered at UA2. Other LHC collaborations were under consideration at the time, which would have had very rigid, top-down hierarchies. That way of doing physics is just completely anathema to me; it leads to decisions being made that have nothing to do with physics. Luckily, the LHC collaborations avoided taking that route.

That said, I missed the early days of ATLAS’ formation. I left CERN in early 1990 to work at LBNL, and totally immersed myself in work on the Superconducting Super Collider (SSC) by joining the SDC experiment, becoming the Physics Coordinator for several years, and producing the physics part of the Technical Design Report (TDR) in 1992. There wasn’t a lot of belief in the LHC programme from many US scientists at the time. It was thought, rather naively, that because the SSC had been under development for so long and used more mature magnets and much larger rings than the LHC, that it was definitely the best way to go. Its sudden cancellation was one of those traumatic experiences that completely changes everything you do afterwards. It was an unbelievable situation. Hundreds of our colleagues got their pink slips, all at the same time. So many people had to leave physics for good.

The sudden cancellation of the SSC was one of those traumatic experiences that completely changes everything you do afterwards. It was an unbelievable situation. Hundreds of our colleagues got their pink slips, all at the same time. So many people had to leave physics for good.

How did the field adapt to this major cancellation? Did it impact the way you approached projects?

It really did change everything. Those of us still employed had to completely reorient our dreams around the LHC. It was the only possible path forward into the TeV range and, for the US, it was still far from a sure thing. In that period, my whole professional life revolved around ensuring that the US could participate fully in the LHC, and that the LHC and ATLAS actually got built. This intense dedication was common at the time, because this was a life-or-death situation for our field as seen from the US side. We referred to ourselves as SSC refugees, looking for a safe harbour.

In the Berkeley group, we chose to look forward and organised initial discussions between our group (George Trilling, Murdock Gilchriese, and myself) to interview both ATLAS and CMS. During that process, we were encouraged by Peter Jenni to use our silicon-detector expertise in the inner detector area, but told that joining ATLAS meant joining the international team – detectors would not be “owned” by national groups. After our experience with losing SDC, we were enthusiastic about this approach. In discussions with CMS, the dialog was oriented towards “owning” parts of the detector that would fit national budgets. We chose ATLAS, and never looked back!

2004: Kevin in the clean-room facility for the ATLAS Inner Detector at CERN. (Image: P. Loiez/CERN)

From my perspective, we urgently needed to define how the US would become a collaborator in the LHC programme. What would be the scale of involvement? How much money would be involved? Could we even get our colleagues and funding agencies on board with the idea of joining the Large Hadron Collider project at CERN?

I had the good fortune to serve on a subpanel of the High Energy Physics Advisory Panel (HEPAP) that was formed to address the issues above. This was the so-called “Drell panel”, chaired by the SLAC theorist Sid Drell, formed in 1994. This panel was unusually well-connected to high levels in the US government. As a young scientist, I focused on physics and technical issues. I had been serving on the CERN LHC Experiments Committee (LHCC) from its start in 1992, and was part of the technical management of SDC. A key point of contention was the LHC’s lower energy that required more intense beams to explore the TeV scale. There were many sceptics who thought it was impossible to do serious physics research with more than ~1 hadron collision at a time. Yet the LHC required more than 20 hadron collisions per beam crossing to achieve its physics goals. That’s hard to imagine nowadays, given the massive number of collisions we see per LHC bunch crossing, but it was still unclear to many in the early 90s. I felt like a big part of my job on the sub-panel was to convince my colleagues of the feasibility of operating in this very high pileup regime. Our panel formally endorsed the US role in the LHC in early 1995, which was a major step forward from the SSC catastrophe.

What was your first role in the ATLAS Collaboration?

I began work on electronics for the ATLAS Pixel detector in 1994, prototyping ideas for front-end designs and readout architectures. Little did I know this would be the start of my long odyssey into beyond-state-of-the-art silicon technology. Over the subsequent 15 years, I saw the Pixel detector go from a pioneering concept to a successful prototype and finally into a working instrument inside the ATLAS experiment. The experience really cemented my belief in building ambitious hardware.

In 2005, I was elected Pixel Project Leader and moved back to CERN with my family. We were facing several new technical and resource challenges at the time – all of which had to be resolved before the looming LHC start-up deadline. We successfully installed the Pixel detector in June 2007, just in time. The Endcap Toroids were to be installed in July 2007 and, if the Pixel installation had fallen behind schedule, we would have risked not being ready for first collisions. The Pixel detector was ready for commissioning in 2008. This final push over the finish line was only possible thanks to the Pixel team’s tireless efforts.

2007: Kevin in front of the ATLAS Pixel detector after the successful insertion of the detector into its carrier. (Image: C. Marcelloni/CERN)

With the Pixel detector complete, you soon transitioned to data analysis – becoming ATLAS’ Standard Model convener in 2009 and Physics Coordinator in 2011. What were the main physics priorities in those early days?

As soon as we began recording data, we launched a strategy we dubbed “re-observing the Standard Model”. The first step was to actually understand our signals, learning how to reconstruct/identify/measure tracks, jets, photons, leptons, missing energy, etc. in the ATLAS data. In parallel, we were making the first reference measurements of Standard Model particles. Our group published the very first ATLAS physics analysis paper, on minimum bias events, measuring basic distributions of track parameters. By the end of 2011, we had an unprecedentedly detailed picture of the Standard Model in a new energy regime. Moving to the Physics Coordinator level was an enormous step, and the lead up to the Higgs observation was a unique lifetime experience – this story has been told many times already. I consider Physics Coordinator to be the best and most exciting job in ATLAS, and am grateful for the opportunity I had to be in the right place at the right time.

What amazed me was the change in the group dynamics at this time. We’d spent years preparing a lot of these analyses and, when we had no data, that work was driven by the most senior people. Once we had data, all of a sudden the plots started coming from completely different corners of the community. Fellows, graduate students and postdocs left all the senior people in the dust – myself included – producing remarkably high-quality physics results.

I think it had a massive impact on their confidence in their future careers. Because even though they were part of a huge collaboration, they were very empowered. It was an environment where they had to do a lot of thinking on their feet, constantly inventing new tricks. There was no playbook to follow. If they found that a bit of software wasn't working, for example, it was all on them to come up with ways to get around the problem. From my side, it was really exciting to watch these young people grow their skills and absolutely thrive.

Once ATLAS had data, all of a sudden the plots started coming from completely different corners of the community. Fellows, graduate students and postdocs left all the senior people in the dust – myself included – producing remarkably high-quality physics results.

You moved back into detector development in 2013, first working on the Insertable B-layer sub-detector and then focussing on ATLAS upgrades for the High-Luminosity LHC (HL-LHC). What inspired the move?

I just really believed in the HL-LHC programme and wanted it to succeed. By that time, I had collected a unique assortment of skills both in physics and detector design, and there was a lot of work to be done on the upgrades. Although there had been plenty of discussions, I felt the Collaboration hadn’t made enough progress in turning our ideas into concrete projects. What would the final designs be? How many people would we need to build these upgrades? How much money would it cost? Could we actually make the things we were talking about? And then, could we go out to funding agencies to convince them?

It was clear that we needed to take a fresh look at our HL-LHC upgrade plans and ask some hard questions. At the time, my main concern was: were we being sufficiently ambitious? This was also echoed by the LHCC reviewers of our initial Letter of Intent for the upgrades.

That’s interesting – because typically the feedback experimentalists get is that they are being too ambitious.

That’s true, but it’s important to also match the scale of the project. Data-taking in HL-LHC will generate around 95% of ATLAS’ lifetime dataset – clearly the upgraded detector needs to be the best it can possibly be.

In 2014, we developed a weekly task force that would explore some outside-the-box ideas. In particular, I thought that we could really improve our forward detectors in order to study vector boson fusion in detail. This led to the design of the new Inner Tracking detector, which will be unlike anything that has been built for a hadron collider. We also explored extensions to the detector’s magnetic field coverage, improving how we track muons, and identified precision timing as another key point and led to the development of the High-Granularity Timing Detector. Not all of the ideas made the cut into the final HL-LHC detector, but many did, helping to ensure ATLAS would continue to lead in the coming decades.

I was certainly among those pushing for ambitious designs, wanting to improve the ATLAS detector as much as we possibly could. ATLAS is a huge collaboration of extremely talented people – I believe we can do the work. Now, some elements of the upgrades may end up being beyond our reach. But I didn’t want the field to look back on these decisions, 15 years from now, and say “why didn’t they do more?” We still don’t know what will come next after the HL-LHC. We need to take full advantage of the present HL-LHC opportunities!

I don’t want the field to look back on our upgrade decisions, 15 years from now, and say “why didn’t they do more?” We still don’t know what will come next after the HL-LHC. We need to take full advantage of the present HL-LHC opportunities!

You ended up becoming ATLAS Upgrade Coordinator in October 2014. How did you set out to put these ambitious designs on schedule for HL-LHC?

Images of ATLAS Phase 2 Technical Design Reports and Technical Proposals. (Image: E. Ward/ATLAS Collaboration)

Within two weeks of my election, and before my term started, we launched a new “scoping document” process, jointly with CMS and the CERN Director of Research. This was a formal procedure to evaluate the cost and feasibility of the upgrades. We wanted to put forward a range of options for different costs and ambitions: low, medium and high. This would then be used to define the final scope of the upgrade project. It was not yet clear how much an HL-LHC detector should cost, and there is a tendency in the field to define the scope of a project by the budget available. That’s really not the right approach for a project as large as this one. This scoping process gave us a chance to explore several options, balancing cost against the possible physics performance. By examining three scenarios, we could make a very clear and compelling case for the most expensive option. This process took about a year, and by September 2015 we had a very clear idea of what we would build.

This set us up well for the next stage: creating the upgrade TDRs. I am very proud that, despite several challenges, we completed and published all six upgrade TDRs by the end of 2017. We were then able to formally submit the Memorandums of Understanding to funding agencies in 2019. This was an extremely quick turnover, considering the number of R&D, performance and physics studies each report required. The ATLAS upgrade community is extremely dedicated, and I have every confidence in their success going forward.

What do you think are the key challenges for ATLAS going forward?

I think Run 3 will be a critical phase for the ATLAS Collaboration; there’s a lot of work we have to do in parallel. A lot of dedication will be needed to construct all of our new detectors. This work will be an investment in the future, as the HL-LHC is the most important project of the global accelerator-based particle physics programme. That said, the start of the HL-LHC is still a long way off. We need to keep up the pace of our data analysis, as the future of our field depends on the success of our current physics programme.

ATLAS Portraits is a series of interviews presenting collaborators whose contributions have helped shape the ATLAS experiment. Discover more ATLAS Portraits here.

In conversation with John Rutherfoord, a leading designer of the ATLAS Calorimeter

Katarina Anthony — Thu, 22 Apr 2021 14:51:28 +0000

In conversation with John Rutherfoord, a leading designer of the ATLAS Calorimeter

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Katarina Anthony Thu, 22/04/2021 - 16:51

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John P. Rutherfoord is a professor at the University of Arizona and a long-standing member of the ATLAS Collaboration. His extensive career has taken him from searching for the Upsilon particle at Fermilab to CERN to leading the design and development of the ATLAS Forward Calorimeter.

Portrait of John Rutherfoord, Regents Professor, Department of Physics, University of Arizona. (Image: John Z. de Dios)

At a very early age, I pictured myself working in a college atmosphere. There was no question in my mind that I was going to be a physics major and that I was going to go to grad school. I’m not sure where my conviction came from – I hadn’t yet taken a physics course and I didn’t really know what grad school was – but I set my mind to getting there.

It wasn’t simple, though. In my junior year of high school, I realised that I needed to understand calculus to address the physics questions that I was playing with. But my school didn’t offer the subject and I found that almost none of the math teachers knew calculus. Luckily there was one teacher, Mr. Barlow, who did and he was willing to teach it to me after school. Each afternoon I would have a class with him and he gave me homework problems to work on before our next meeting. He made a huge difference in my life, not just by teaching me calculus but also by encouraging me to pursue math and science. I learned an awful lot from him.

The work paid off and I did my BSc in Physics at Union College (US), a Ph.D. in Experimental Particle Physics at Cornell University (US) and did some of my first post-grad work at the Cornell Synchrotron Lab.

Small experiments, big results

Back in those days, experiments were much smaller and, as a consequence, there were many more of them. My thesis experiment at Cornell consisted of just three scintillation counters, a beam line I constructed, and a few home-made fast electronics modules constructed by an earlier grad student, Walter LeCroy.

That was typical of the time. Experiments were specialised in doing one thing and doing it well. I was able to see experiments through their entire lifetime: from concept and funding, to design and construction, and finally data-taking and data analysis.

As a postdoc at the University of Washington I was stationed at Fermilab. My first job was as deputy spokesperson for an experiment that observed the Upsilon particle shortly after Leon Letterman’s team. Our detector’s mass resolution wasn’t as good as Leon’s – so our signal wasn’t as clear – but we could take higher rates and so we saw more of the Drell-Yan continuum above the Upsilons. These were exciting times.

I was able to see experiments through their entire lifetime: from concept and funding, to design and construction, and finally data-taking and data analysis.

Shortly after, I was invited to join Leon’s team for a follow-up experiment similar in concept to the Upsilon discovery experiment, but at a much bigger scale. Having learned the importance of good mass resolution, I realised that a different approach, which would require only minor modifications to the experiment, would improve our resolution by a factor of ten. My concept was immediately accepted by the team, and we put it together in just a few months.

It was a fantastic detector with mass resolution comparable to what's obtained at electron-positron colliders. In 1984, while we were taking data, a team at DESY announced that they’d observed a new particle thought to be a Higgs boson. I realised that if they had found the Higgs boson, our detector would have also seen it. We scoured our data and were able to rule out that possibility. Somewhat later, the DESY team found they had made a mistake in their analysis and withdrew their claim.

Arizona Bound! From the SSC to ATLAS

In 1988, I was asked by the University of Arizona to consider forming a new experimental-particle-physics group. I faced a difficult decision, as I loved my position at University of Washington, but this was an opportunity to build a team from the ground up. I accepted the offer. One of the first things I did was to recruit my friend and colleague Mike Shupe, who is well known to many in the ATLAS Collaboration. We spent the next several years building up our team, developing expertise and really putting the university on the particle physics map.

Even before moving to Arizona, I had started to get involved in the Superconducting Super Collider (SSC), and so it was one of our team’s first projects. We led the Forward Calorimeter effort for the GEM experiment, which became one of the two approved experiments for the collider. It was an interesting time for the particle-physics community, as physicists on the SSC were somewhat in competition with those at CERN. Despite that, there were still opportunities for collaboration.

Similar to ATLAS, the Forward Calorimeter design for GEM used liquid argon. And so when Daniel Fournier – who first proposed the accordion calorimeter design – visited the SSC headquarters in Dallas in the early ‘90s, it was a rare opportunity to share with him what we were doing. Shortly thereafter, we were invited (very indirectly, mind you) to test our forward calorimeter prototype at a test beam in CERN’s North Area.

That’s where we were in the autumn of 1993, when the US Congress decided to kill the SSC. Our little calorimeter prototype was working marvellously and we were overjoyed. People would come by – standing at what we now call a social distance – just to watch our progress. But by the end of our trip, our eyes were only on our emails, as we watched the cancellation decision come through.

It was rather natural that, very soon after the SSC’s demise, our team approached ATLAS about the possibility of joining. We knew we could make a big contribution and we had resources that would really benefit the project. We became unofficial members that same year and started attending regular meetings in early 1994 – arguing for the design of the ATLAS Forward Calorimeter system.

Several good proposals for the Forward Calorimeter were being considered, and no decision had been reached in early 1994. At the time, it was not appreciated that the ATLAS cavern would light up with background radiation. My colleague Mike Shupe made a huge contribution very early on, by making a detailed calculation of the expected background radiation in the ATLAS cavern. He was able to show, very clearly, that several of the proposals still on the table would have led to unacceptable backgrounds, particularly in the muon system.

Despite the physical distance between Arizona and Geneva, we never felt like we were out here by ourselves. Our work was done in a close collaboration with the whole liquid-argon team, and we all became lifetime friends as a result.

An ATLAS calorimeter review committee was appointed to choose one of the Forward Calorimeter proposals. In the summer of 1994, our proposal was selected. One of the first things we did was to get more teams on board, in particular the University of Toronto and Carleton University in Canada, and ITEP in Moscow. Our partnership with them worked out perfectly as, when we moved into the construction phase, they were interested in doing hadronic modules and we focused on the electromagnetic modules.

Despite the physical distance between Arizona and Geneva, we never felt like we were out here by ourselves. Our work was done in a close collaboration with the whole liquid-argon team, and we all became lifetime friends as a result. Most of these interactions took place at meetings at CERN, so we were traveling back and forth all the time. I remember one year I was at CERN more than 25% of my time, all while teaching classes here in Arizona. In retrospect I'm not sure how that worked out; I grew quite accustomed to the long journey.

Once our Forward Calorimeter concept was accepted, I became the leader of the Forward Calorimeter Construction Project within ATLAS. Arizona led the construction and the electromagnetic modules were actually built in our physics department’s basement, where we involved a lot of students. The finished modules were shipped to CERN in 2003 and a lot of our technical people moved out with them. They spent several years integrating the modules into the two forward calorimeter units, and then testing and installing them into the experiment’s cryostats.

Group photo taken on the occasion of the first of the two Forward Calorimeters being installed in the end cap cryostat, then located in CERN’s building 180. The yellow fixture is attached to the end plate of the enclosing cylindrical housing with the Forward Calorimeter modules within. From left to right: physicist/engineer Alexandre Savine (Arizona), technician Philippe Gravelle (Carleton), physicist Peter Loch (Arizona), project leader of the Forward Calorimeter construction project John Rutherfoord (Arizona), technical coordinator for the Forward Calorimeter construction project engineer Leif Shaver (Arizona), and engineer Mircia Cadabeschi (Toronto). (Image: Roy Langstaff/ ATLAS Collaboration)

Want to construct a detector? Seek out new opinions

Having a broad perspective, some gained during the SSC days, and input from several different experts was critical throughout the construction process. I remember sitting in a committee meeting in the early 1990s, discussing how we would maintain certain aspects of the detector. One rather prominent physicist suggested that we could just put up a stepladder to work on a piece of the calorimeter. He had no concept of how far off the floor the detector was, or even how big it was. It caught me by surprise.

This is where engineers are invaluable and I’ve worked with some very impressive engineers over the course of my career. They would often sit in on our meetings, listening to our debates over particular types of technology. In one meeting, I remember one of these top-notch engineers making a point. He said, “what we can do is make sure that your detector stands up. Not that it works. Just that it stands up.” That’s why we need different types of expertise. We were worried about whether we were developing the best technology for the application, while the engineers worried about whether it would stand up.

A top-notch engineer told us, “What we can do is make sure that your detector stands up. Not that it works. Just that it stands up.”

When the construction was largely completed, we all were asked to write what I call an as-built document describing a part of the ATLAS detector. I wrote the section on the Forward Calorimeter, along with Gerald Oakham, a Canadian colleague. Different groups took different approaches to this document, but I chose to focus on why the Forward Calorimeter was designed and built the way it was. This is something I think is missing from a lot of experimental papers which just focus on listing facts. That ignores a fundamental part of the process: the why is the art of designing a successful detector.

When we don’t share how we arrived at our decisions, we communicate a strange message to the physicists who come after us. A lot of my students don’t think to ask why ATLAS is the way it is. They just accept it. But that assumes the detector was the best it could be, which it wasn’t. It came about from past experience, technological breakthroughs, aggressive thinking, political necessity, the best decisions we could make at the time, and a lot of compromises.

Speaking to those younger physicists I would say you don’t need to wait until you’re a senior researcher to make change – so long as you’re willing to push for an idea and to gather people around it. The whole process of launching your own project is so much fun, and I would certainly encourage young people to try their hand at it. Choose a compelling physics topic that would be key to the collaboration, and then figure out how to get it done. Some of the most exciting new projects under development right now came about exactly this way.

You don’t need to wait until you’re a senior researcher to make change – so long as you’re willing to push for an idea and to gather people around it.

My focus these past few years has been on the upgrades to the detector. In particular, I’m interested in understanding how the electrical pulses from some parts of the calorimeters will change as the luminosity of the LHC increases well beyond the original design value. These changes will require modifications to our treatment of the data and it’s not yet known what these modifications will be.

I see the focus of the ATLAS Collaboration shifting even further towards perfecting the performance of our detector to get high-quality data, first by following through on our upgrade plans which will enhance the detector’s capabilities and second, through continuous improvement of data analysis strategies. We’re looking at a future with an exceptional quantity and quality of physics data – and with it, hopefully, big new discoveries.

ATLAS Portraits is a series of interviews presenting collaborators whose contributions have helped shape the ATLAS experiment. Discover more ATLAS Portraits here.

In conversation with Claudia Gemme, an influential voice in ATLAS detector upgrades

Steven Goldfarb — Mon, 15 Jun 2020 11:49:00 +0000

In conversation with Claudia Gemme, an influential voice in ATLAS detector upgrades

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Steven Goldfarb Mon, 15/06/2020 - 13:49

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Portrait of Claudia Gemme, ATLAS ITk project leader (Image: N. Darbo)

Claudia Gemme, researcher at INFN in Genova, has had a varied career with the ATLAS Collaboration. From her work on the construction and commissioning of the ATLAS Pixel detector, to a career in physics analysis and the ATLAS Publication Committee, she now leads a key upgrade of the ATLAS detector: the ATLAS Inner Tracker (ITk).

I was not one of those kids who said, from the very beginning, I want to be a physicist. That being said, there are certain moments of my childhood which were, in retrospect, turning points. As a child, going to work with my mother gave me my first experience with physics. She was a radiologist, and would take me into the hospital dark room to watch how she developed x-ray images.

Then, in high school, I followed the news coverage about Carlo Rubbia and his Nobel Prize for the contribution to the W/Z-boson discovery. There was a lot of physics outreach being done in Italy at the time that made a big impact. If you speak to other Italian physicists of my generation, they’ll most probably say the same: this is how a lot of us got into the field. There is something very valuable about seeing your potential career in practice, and it pushed me to study physics at university.

I graduated in 1993 with a degree in theoretical nuclear physics at the University of Genova, and was looking for direction for my PhD. Fortunately, I had an opportunity to visit CERN during my Masters studies. It was a great visit and left me wondering if this could be a place for me.

Soon after, I ran into my future-supervisor Bianca Osculati. She was heading on a long walk across campus and I joined her, asking her career advice and expressing my interest in spending a few months at CERN. She was a fantastic support and invited me to apply to a PhD position in her group, working on the WA92 experiment on the Super Proton Synchrotron (SPS).

Joining Bianca’s group was a completely new experience for me. The experiment had just ended data taking, so for three years I worked solely on data analysis. I felt like I knew next to nothing about the field when I started, but I had an excellent group and role models around me.

Then my life underwent a number of big shifts. On the personal front, I had my first child while completing my doctoral studies and, at work, I moved from WA92 to the newly-formed ATLAS Collaboration. I was fortunate enough to join ATLAS right when the collaboration was developing – a great opportunity, especially for a student.

Construction of the ATLAS Pixel detector in Genova. (Image: N. Darbo.)

In 1998, my team suggested I shift my focus from analysis and simulations, to working in the lab on hardware. Genova was taking a leading role in the R&D and construction of the Pixel detector, and I was able to join in at an early stage of the development. I was surprised to find that I loved the work as, in university, I had found working on hardware confusing and frustrating.

The ATLAS Genova team provided an excellent education; I think I learned more in those few years than any other time of my life. I was exposed to so many experts from so many fields – physicists, technicians and engineers – with so much expertise to share. In particular, I also developed excellent synergy with the technicians, who have an incredible knowledge to share. In many respects, my role was simply to apply a formula to what they already knew.

From 2002, I was responsible for the Pixel module construction in Genova, overseeing the team there. As construction wrapped up, our work shifted to testing and then, as the detector moved to CERN, I moved with it to work on integration. By the time we finally installed the detector, in 2007, I had been with the project for almost eight years.

Those last few years were very stressful. Along with the pressures of the schedule and the large amount of challenges that had to be overcome, I was also balancing a (more important) personal project: raising my three young children. The day of final installation was thus very emotional for us all. I can really only compare the feeling to the birth of a child, albeit on a different level. But then the story continued, and I took on more responsibilities: overseeing the commissioning of the Pixel detector and becoming Pixel Run Coordinator.

Those last few years working on the Pixel detector were very stressful. Along with the pressures of the schedule and the large amount of challenges that had to be overcome, I was also balancing a (more important) personal project: raising my three young children.

When I finally returned to Genova in 2009, I ended up shifting paths to work in data analysis. This was a tough transition at first. I went from being in charge of a big team, focussed on immediate deadlines, to being by myself. Fortunately, the work was really interesting. Within a few months we had the first ionisation results using cosmic rays and then, once collisions started, one of the very first ATLAS plots was from our team. I still keep its CERN Courier write-up in my office.

Having experience in both analysis and hardware turned out to be a boon for my career, leading to my appointment on several review boards and on the ATLAS Publication Committee. While I found both areas are very satisfying to work in, data analysis is not as tangible. Though conferences can give you that boost to complete your analysis, the deadlines in hardware are stricter. If a system needs to be online tomorrow, you don’t go home until you are done. Although at times a bit stressful, I found this really rewarding, as you feel that ATLAS relies on you to operate. I like to feel the pressure and solve problems – and hardware work provides both of those things.

Type-0 tapes for ITk Pixel Outer End-Cap, just arrived from CERN (May 2020). (Image: E. Ruscino)

Nevertheless, for quite a few years I was able to just enjoy the success of the detector and study its data. I tried to stay out of upgrade work, with just some participation in R&D and in the newly formed ITk collaboration. My strategy worked until 2015, when I was asked by ITk project leader Steve McMahon to co-chair the ITk layout taskforce. Little did I know this was his way of subtly bringing me back into the fold. From there, I was also involved in editing the Technical Design Reports and, in 2017, Steve asked me to become his deputy. Just as suddenly as I had left, I was back to working on hardware almost full time.

As the ITk project leader, I’d say my main activity is dealing with day-to-day problems. I do not assume I can follow – nor do I think I should – every single detail of the project. Instead, I trust that the level of coordination below me has a strong understanding of the details and has handled them competently. My role is to have a deep enough knowledge to understand the gravity of any problems, and monitor that the flow of information is working correctly, not only towards me, but also within the teams.

It is in the very nature of our project to have a lot of problems. Our work is at the frontier of the field and every action we take is charting new waters. It never goes smoothly and we have to expect setbacks as we progress. That being said, though I spend most of my time resolving problems, the majority of news is good news. But as it doesn’t require action, it can sometimes skew the way we think of our progress.

The ITk project is now entering an exciting phase, no longer focused on R&D but instead on the path to construction. This requires a shift in mentality, and I think I am perhaps more cautious than some colleagues. Our community is highly dominated by optimists, always looking to have the very best technology they can. But at some point, you need to put down the pen and start the process. I am in favour of compromise, focusing on what we can do rather than pushing for what people would like to have.

Our community is highly dominated by optimists, always looking to have the very best technology they can. But at some point, you need to put down the pen.

Keeping people motivated during construction will be tough. While it does require a lot of detailed repetitive work, it brings with it a unique set of challenges that can keep you engaged. During the Pixel detector’s construction, for example, I found some of my most interesting work in our “module hospital”, where we had to find and resolve new problems.

It will be a challenge to build the ITk – both on a technical and human level. As management, it is our responsibility to keep the motivation and focus high, while also acknowledging that the work may be tedious at times. Our project is dependent on motivation at every level – from students to coordinators to technicians – and we must ensure they feel recognised for their hard work.

It is also vital to form good, personal connections with institute teams, on whom the entire project will rely. I try to meet with people in person, to put a face on the idea of “management”. When that’s not possible – as is the case at the moment – I answer a lot of emails. It is my belief that a successful manager not only keeps their project on track, they also make people’s lives happy while they are part of the project. I try to listen and engage in one-on-one contact. Maybe I don’t always succeed, but I try!

Building a new detector is an incredible opportunity – one that I hope my younger colleagues take advantage of. I have been fortunate enough to see the ATLAS detector at every stage of its life: through R&D, production, installation and data-taking. Now, my hope is that others get to experience the same.

Aside from the professional rewards, I’ve also gained wonderful friendships. Big challenges generate strong and deep interpersonal connections that go beyond the work. I still have close bonds with the people I worked with on the Pixel detector, even if we only see each other very rarely. I have that same feeling these days when working on the ITk – like I am with a group of lifelong friends. Together, you become part of something important that not only shapes the field, it shapes the people.

Celebrating a milestone with friends and colleagues in Genova (March 2013). (Image: N. Darbo)

ATLAS Portraits is a series of interviews presenting collaborators whose contributions have helped shape the ATLAS experiment. Discover more ATLAS Portraits here.

In conversation with Philippe Farthouat, a driving force behind ATLAS electronics

Steven Goldfarb — Tue, 14 Jan 2020 10:24:00 +0000

In conversation with Philippe Farthouat, a driving force behind ATLAS electronics

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Steven Goldfarb Tue, 14/01/2020 - 11:24

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Philippe Farthouat. (Image: C. Nellist/ATLAS Collaboration)

Philippe Farthouat has played a critical role in electronics development since the beginning of ATLAS, from design and prototyping to testing and installation. He has been the overall ATLAS electronics coordinator since 1999.

In 1977, I started my first job out of university working at a nuclear-physics laboratory in Saclay, France. After a few years there, I moved to a department collaborating with CERN and was assigned to work on the OPAL experiment on the Large Electron-Positron Collider (LEP).

As the experiment geared up for installation, my work on OPAL required me to be on-site full time. I had to make a decision: I could make the journey back and forth from Paris to CERN every week, or I could just move. My wife and I were soon expecting our third daughter, and a commute would never have worked. We moved to the area in 1988 and have been here ever since.

Two years later, I was offered a CERN staff position as a group leader in the Electronics & Computing for Physics (ECP) department. I thought they were a bit crazy, because I had no management experience – but I took on the challenge nevertheless. The group was in charge of designing the electronic systems for several experiments, in particular the Omega Spectrometer and the LEP collider, as well as the first R&D programmes for the LHC.

The BEATRICE experiment, for which Philippe and his team were in charge of the readout electronics, here pictured after its installation in the Omega Spectrometer in 1991. (Image: CERN)

There were a number of these programmes starting at that time, looking at many different types of detectors that could be installed on the LHC. At the time, it was not yet clear if we could even make a detector for it. ATLAS was not yet a collaboration, so it is hard to say when my “real” work on it began. But, as a matter of fact, my group was involved in R&D for detectors which were later integrated in ATLAS. For instance, I remember that the very first day I came in my office as a CERN staff member, I had a letter waiting on my desk from Chris Fabjan – who would become the ATLAS Muon Project Leader – asking for help developing the electronics for what would become the ATLAS Transition Radiation Tracker (TRT). Thus, when ATLAS formally became an experiment, my group was naturally selected to focus on its development. So, it’s not that I chose ATLAS because I thought it was the best proposal, but I never regretted it.

My group was involved in a number of ATLAS projects, including the TRT readout electronics, level-1 central trigger logic, TTC (timing, trigger and control) distribution and readout links (S-Links), as well as general support and electronics coordination.

It was clear very early on that the amount of electronics to be installed in the LHC experiments, as well as their complexity and cost, would require dedicated scrutiny (which was not really the case before the LHC). This led CERN to establish the LHC Electronics Review Board and to the LHC experiments to put in place internal electronics coordination. ATLAS elected Brig Williams from the University of Pennsylvania as the very first electronics coordinator in 1996, and I served as his deputy until taking over the role in 1999.

We faced several significant challenges, especially at the beginning. ATLAS needed electronics that could last several decades, be built on time at low cost and be compatible with the overall trigger and data acquisition architecture. And, if that weren’t enough, we soon realised that the issue of radiation hardness for the front-end electronics was going to be a major obstacle, though it was not yet clear, at that time, exactly how significant an issue this would turn out to be.

In the mid-90s, the only radiation-hard electronics that had been developed were for military or space use. That was a problem not just in terms of accessing the technology, but because the cost was outrageous. For a while, we only had this small selection of options we could explore. None of them were high-volume, cheap, nor easy to handle.

Luckily, we had a change of thinking about the problem; Erik Heijne, a senior member of the CERN micro-electronics group, suggested that we use instead a commercial, deep submicron CMOS technology. While not developed for a radiation environment, the major concern was leakage current – which we could resolve with well-known solutions (using enclosed gate transistors). This was a big step forward, as CMOS had all the benefits of being extremely well-established, having a high-volume production line and fast turn-around, all at a cheaper cost.

Thus, many of our designs moved away from special radiation-hard technology to this one. Of the very radiation-hard integrated circuits (ASICs) designed for ATLAS, 12 needed bipolar devices and used a special technology, while 11 were CMOS devices which moved to the commercial technology. The experience taught us a great lesson that is often tempting to forget: if you can use mainstream technologies, do so. A custom solution may look good on paper, but that does not account for the incredible difficulties that you will inevitably encounter during production and testing.

While other difficult problems still had to be tackled – such as grounding and shielding, power distribution, standardisation of devices, etc. – I think it’s worth remembering how difficult the issue of radiation hardness was for us. It took a long time to put in place procedures to validate the electronics against radiation and to get them “happily” applied. This issue remains very important and will even be more acute in the future.

We always do our best to validate electronics designs through internal reviews. This process creates a lot of work for ATLAS members and the electronics coordination, and I have to thank all colleagues who have played and still play the game very openly and constructively as this procedure would not work otherwise.

Reflecting on past and on-going projects, I think it is also crucial to have realistic expectations of performances and schedule. I have almost never seen a project run on time, as there are always unexpected roadblocks for even the best-laid plans. We should always take into account that we will be slower than anticipated. We often forget that the actual schedule of the LHC has been very different from what was initially foreseen.

It is crucial to have realistic expectations of performances and schedule. I have almost never seen a project run on time, as there are always unexpected roadblocks for even the best-laid plans.

In particular, for the electronics, the issue of radiation hardness will continue to haunt us at the High-Luminosity LHC (HL-LHC). The inner part of the detector is really an unfriendly area for electronics. You have to use a lot of tricks and try to anticipate any possible problem. Even when you do whatever you can, radiation will be a constant issue during the lifetime of your experiment. At the HL-LHC, it will not only be the radiation dose that causes difficulties; single-event upsets will remain a major, less predictable problem. Single-event upsets occur when a single ionising particle travels through a chip and causes a sudden change of state. They are never fully uncovered until you reach the prototyping phase, and such a discovery can cost you a lot of time. Once you identify that there is a problem, you then have to try to validate exactly where it comes from. This is done by shooting suspected problem areas with a laser or micro-beam to induce the failure. Then it comes to working out how to correct the issue. This can all take a lot of time; for instance, the recent problems discovered with the low-power gigabit transceiver (lpGBT) induced a full year of delay.

Sometimes, maybe because I am getting older, I think people gravitate towards solutions that put too much complexity not only in the front-end electronics, but also in back-end systems which have to run and require updates for 20 years. Looking at what the requirements will be for far-future colliders, such as the Future Circular Collider (FCC) trackers, I wonder whether we should shift our thinking towards developing systems that are easily replaceable. These would thus have less demanding environmental requirements and could be built in larger quantities. Such "Kleenex detectors" may be the solution for extremely tough radiation environments.

We need to be constantly considering the next project on the horizon, while still finalising the current one. Even when you don’t have all of the details you will need and aren’t sure what the environment will be like, you have to begin designing, prototyping and testing. Your design at this stage may never be used, but such continuous work is essential to any experiment's progress.

It must also be kept in mind that, contrary to what industry does, we take years to design our complex chips. During that time, the technology you use is aging and you have the risk that it ages so much that the factory delivering it decides to abandon it. You have to monitor the situation carefully.

Overall, ATLAS and the LHC are incredible success stories – but that came after years of development and several delays. We should remember that it was not an easy achievement at all. I will be retiring soon, and am looking forward to spending more time with my wife, daughters and grandchildren. I also anticipate observing the novel solutions my fellow ATLAS members will develop, as they continue the legacy we started years ago.

ATLAS Portraits is a series of interviews presenting collaborators whose contributions have helped shape the ATLAS experiment. Discover more ATLAS Portraits here.

In conversation with Masaya Ishino, a key player behind ATLAS' successful Run 2

Steven Goldfarb — Mon, 07 Oct 2019 11:03:00 +0000

In conversation with Masaya Ishino, a key player behind ATLAS' successful Run 2

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Steven Goldfarb Mon, 07/10/2019 - 13:03

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Masaya Ishino, ATLAS Run Coordinator (2017-2018), in the ATLAS control room. As he shows the impressive ATLAS Run 2 luminosity plot, the Gruffalo looks on. (Image: M. Brice/CERN)

“I always do that, get into something and see how far I can go.” ― Richard P. Feynman.

Like many physicists, Masaya Ishino was inspired to join the field after reading the works of Richard Feynman as a teenager. Surely, he thought, if I become a physicist, my life will be as fun as Mr. Feynman’s. Today, Masaya is a researcher and professor with the University of Tokyo. He joined the ATLAS Collaboration in 2001, and has been instrumental to the development, construction and operation of the muon spectrometer. Masaya was elected ATLAS Run Coordinator in 2017, playing a key role in the record-breaking Run 2 operation.

I began my career at the now-retired KEK Proton Synchrotron, working on a very small experiment – with only six students and one supervisor. I had the opportunity to experience every phase of the experiment, from design and construction to data taking and physics analysis. In such conditions, I could decide everything, in principle. We were only a few people, and all of us were true experts on the experiment. We knew each other very well, and everyone understood the experiment deeply.

While such a situation is quite different to those at ATLAS, there are still several similarities. For example, in small experiments, many things are often entrusted to just one person. I think we still see such a thing in ATLAS. There are several cases here where a very important subject can be the responsibility of a single person the experiment relies on.

As a university professor and supervisor, I find this means that my students can play a very important role in ATLAS, albeit with a narrow scope. Despite its size, there remains potential to gain recognition within the large ATLAS Collaboration, as my student Takuto Kunigo did last year when he won an ATLAS outstanding achievement award. He was able to find a good topic and do it well, making a substantial contribution to the collaboration. In this respect, it is similar to what I did in my small-size experiment.

Providing such opportunities to students can be simple when experts, over the course of their work, keep up a list of tasks that would benefit the experiment. Such lists of needed and simple-to-start tasks can allow supervisors to easily find useful ways for their students to contribute.

Operations were very different in the early days of ATLAS. Much had to be done manually and many parts of our systems relied solely on expert intervention.

After I completed my PhD, it seemed only natural to me to join one of the teams working on the ATLAS experiment. I joined the University of Tokyo team in 2001, developing and constructing Thin-Gap Chambers (TGC) for the muon spectrometer, and soon moved to CERN to work on their installation and commissioning.

During this period, our team very carefully designed procedures not only for the installation of these detectors, but also their regular testing. This meant that, on the first day of collisions, we only had to make a single small adjustment to the trigger timing in order to synchronize it with the LHC clock. It was thus one of the first ATLAS systems to accomplish this, I think in large part owing to these rigorous preparations. It was just after this start-up that I took on my first operations role, as part of the TGC team.

Operations were very different in the early days of ATLAS. Much had to be done manually and many parts of our systems relied solely on expert intervention. As we accumulated experience with our detector, we learned what could be considered a typical programme to be fed back into the system for automation. Indeed, I think that the main difference between Run 1 and Run 2 – at least, in terms of operations – is automation. During the entire Run 2 period, we were able to make continuous improvements to our data-taking efficiency through automation in all the ATLAS systems. While there can be some trade off, I believe it remains important to scrutinise any place that can be automated, as that will improve our data taking performance for Run 3 and beyond.

2007: Members of the TGC team in CERN's Building 180, where the detectors were assembled. From left to right: (standing) Vladimir Smakhtin, George Mikenberg and Meir Shoa; (sitting) Shuji Tanaka and Masaya Ishino.

I moved back to Japan in 2011, beginning a new job at Kyoto University. While I spent significant time teaching undergraduate and graduate students, about a third of my time could still be dedicated to working on the muon spectrometer. During Run 1, we found a problem with the purity of the events selected by the TGC trigger. The data sample was polluted with background events likely because of slow protons coming from the end-cap toroid.

When faced with such an issue, immediate action has to be taken. Our team took the issue seriously and defined a programme to resolve it. Such joint action – whether they are developed over organised meetings or simple corridor conversations – is what leads to the most successful solutions. In this case, we input information into our trigger from detectors preceding the toroid to dramatically improve the purity of the sampled events.

My tenure as Run Coordinator was made more eventful by the appearance of the troublesome “Gruffalo” in the LHC beam.

In 2016, I accepted a professorship with the University of Tokyo and once again found myself based at CERN. The following year, I was elected deputy Run Coordinator by the collaboration. Despite my prior experience in operations, taking on the role opened my eyes to the many interconnected systems at play in our experiment: from our small forward detectors to the LHC itself, every part plays a crucial role.

My tenure as Run Coordinator was made more eventful by the appearance of the troublesome “Gruffalo” in the LHC beam. The issues began in the summer of 2017 when, at one specific part of the accelerator (denoted “16L2”), the proton beam would frequently become unstable and have to be ejected. If allowed to continue, the Gruffalo would have significantly limited our data-taking plans for Run 2.

2018: Run Coordinator Masaya Ishino (left) and deputy Run Coordinator Kerstin Lantzsch (right) in discussion as the first proton beams of 2018 circulate in the LHC. Behind them (from left to right): Deputy Spokesperson Isabelle Wingerter-Seez, Spokesperson Karl Jakobs and Karolos Potamianos. (Image: C. Bernius/ATLAS Collaboration)

What was the cause of this instability? Investigating the problem, the LHC team found that the Gruffalo only seemed to awaken when the number of proton bunches in the beam increased. Likely, these were causing an electron cloud to form in the beam pipe. After a few weeks of trial-and-error, the LHC team implemented a new bunch scheme, originally developed as a possibility for the High-Luminosity LHC (HL-LHC). To reduce the buildup of electron clouds, the LHC beam would be filled with a series of 8 proton bunches, followed by 4 empty slots. This proved a success and 2017 data-taking could continue without further surprises, albeit under harsh proton pile-up conditions

Throughout this period, ATLAS operators were constantly on-call. Whenever there was beam loss due to the Gruffalo, the LHC team would want to test out new parameters, such as the bunch intensity or the number of bunches. Not always, but maybe 80% of these changes would affect our operation, and new techniques would have to be developed on the fly.

All of our teams were extremely adaptable, in particular the trigger operations team. There were occasions where I’d have to call them at 3am, describing a new beam configuration that would be in effect in 2 hours and would require a whole new trigger menu. Everyone took their work very seriously, making quick and accurate changes to their systems. Looking back on it, I am still very impressed by their hard work and professionalism. Without all of these committed ATLAS teams, we would not have been able to take such good data that year.

In 2018, we hadn’t expected the Gruffalo to reappear... but it did. The LHC had returned to the normal 25 ns bunch spacing and, for the first part of 2018, data taking went smoothly. But when the Gruffalo reappeared in May, another solution was called for. Taking on board input from all the experiments, the LHC team decided that we could limit the number of protons in a bunch and run continuously. This worked and the Gruffalo went back to sleep, allowing us to have a very good production year in 2018.

New viewpoints are always important, whether they come from other experts or fresh eyes. Indeed, a naïve question, asked in the process of learning, can sometimes point out a problem otherwise overlooked.

While my two-year tenure as Run Coordinator was challenging, I gained a lot of valuable knowledge and experience. An unexpected source of both came from the daily LHC meetings, where accelerator and experiment experts would confer. Prior to joining these meetings, I had assumed it might be difficult to reach consensus between all the experiments. To my surprise, instead they were a good, constructive place for discussion.

Between the experiments, we were almost always able to achieve reasonable solutions through one-on-one conversations. In the rare cases where this wasn’t possible, our discussion would grow to include other experts. Everyone in the room had a broad overview – not just of their system or experiment, but of the machine as a whole. While we all brought different opinions and views to the table, our focus was always to achieve the best possible LHC programme.

Of course, a compromise where no one is satisfied is useless. Yet during my time at these meetings, the conclusions we reached were almost always ones that everyone could be happy with. I am quite proud of what we achieved and would like to express my thanks to the LHC programme coordinators who brought us all together. Without their competent guidance, it could have been difficult to create such a constructive atmosphere.

New viewpoints are always important, whether they come from other experts or fresh eyes. Operating the detector is an important and deeply satisfying task, which should be on the to-do list of all ATLAS members – even those without specific experience. Indeed, a naïve question, asked in the process of learning, can sometimes point out a problem otherwise overlooked. I hope I took such questions seriously during the 2 years I spent as Run Coordinator, and encourage others to do the same.

Since completing my responsibilities as Run Coordinator, I have returned my focus to my research and teaching duties at the University of Tokyo. One of our key tasks is preparing the TGCs to operate at the HL-LHC. As a supervisor, I always try to convey to my students the need to balance different aspects of research for their careers to succeed. If you can fill multiple roles, you will be able to adapt according to the high time. While there will be periods when you can only focus on data analysis, there will be others where hardware or operations experience will be the most needed. Students should prepare in advance to take on these roles.

ATLAS Portraits is a new series of interviews presenting collaborators whose contributions have helped shape the ATLAS experiment. Look forward to further ATLAS Portraits in the coming months.

In conversation with Zachary Marshall, a leading voice in the search for new physics

Steven Goldfarb — Fri, 05 Jul 2019 11:06:00 +0000

In conversation with Zachary Marshall, a leading voice in the search for new physics

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Steven Goldfarb Fri, 05/07/2019 - 13:06

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Zachary Marshall in CERN's Building 40. (Image: E. Ward/ATLAS Collaboration)

Simulation and supersymmetry, two things that have defined Zachary Marshall’s career. Zach is a researcher with Lawrence Berkeley National Lab. He is currently the co-convener of the ATLAS Supersymmetry group, leading the team searching for supersymmetry and all its various manifestations, building on his previous work as convenor of the ATLAS Simulation group.

Back in 2005, there were two big (though certainly not equal-sized) new experimental physics facilities whose start-up was on the horizon: IceCube and the LHC. I was completing my undergraduate studies at Berkeley at the time, and found that the most interesting people I knew were high-energy physicists. As one of my former supervisors was joining the CMS collaboration, picking LHC research for my PhD seemed like the obvious choice.

I joined the ATLAS collaboration and, in 2007, moved to CERN for what I thought would be 18 months. After all, the LHC would be starting soon, I would get my hands on some data, then head home and write up my thesis. But when the 2008 “incident” occurred, a lot of us PhD students found ourselves with a real dilemma. ATLAS wouldn’t collect any collision data until 2009, which we needed in order to graduate. I was ready to book a flight home to work on an experiment at Jefferson Lab, before my supervisor, Emlyn Hughes (now with Columbia University), convinced me to stay. We had a really useful discussion, where we went through and re-examined the situation to see how I could graduate working on ATLAS. We picked modelling jet shapes, which is one of the earliest things that you can do with data. That decision made a massive difference in my life as, ten years later, I am still working here at ATLAS.

I began my career in ATLAS working on detector simulations, which I loved doing. I worked on improving our computing performance – in other words, getting every drop of physics possible out of the CPU. For example, at one point, we were spending 5% of our performance time simulating neutrinos. Why would we do that? We can’t see them – so why simulate them at all? Finding issues like these that can be cut is essential to improving the physics performance of ATLAS.

A lot of people, when they look at code performance, focus on which specific lines of code are taking up more time. In simulation, that is helpful, but it is not the whole story. The same line of code could be applied to an electron or it could be applied to a supersymmetric particle – and it matters much more in one case to get the simulation correct. So, you have to have a few different dimensions in view, and take them all into account when looking at and improving the code.

While I think supersymmetry is a beautiful theory, there’s a saying that “you don’t get a vote in Nature”. I hope we find exactly as much supersymmetry as exists in Nature – no more, no less.

Working in simulation gave me a good understanding of the entire detector, and therefore a unique perspective on analysis once I moved over to the ATLAS Supersymmetry group. But, of course, there were teething problems. Happily, we learn from our mistakes. With my first analysis, I had to overcome some simple barriers like accessing the data and figuring out how the software works. For my second search, the difficulty was with working out what the fit was doing, and controlling the background in various ways.

I later inherited a role in Z+jet search for supersymmetry and found a new challenge learning to manage under intense scrutiny. Before a result is published publicly, analysis groups go through intense scrutiny internal to the collaboration. Colleagues who weren’t involved in the result review your team’s work, and try to think of things that may have gone wrong along the way. The Z+jet search was one that a lot of people paid attention to, because there was a potential 3 sigma deviation from the Standard Model. It was our job to defend it, tooth-and-nail.

Going through one of these reviews feels a lot like a PhD thesis defence. No matter what issue your colleagues highlight, you have to have already considered it in your analysis and be ready to explain its impact in great detail. When you’ve worked on a result for a couple of years, pouring your life into it, this kind of scrutiny can often feel quite critical. As though you’ve screwed up.

Learning not to take this critique as a personal attack can be hard, and it’s one of the first things I try to teach my students. I remind them that no one is out to “get them” – rather, our colleagues are out to get the best possible results for ATLAS. They raise questions and concerns in order to ensure no stone went unturned, and the analysis meets the high standards of the ATLAS collaboration.

Now, as convenor of the Supersymmetry group, I often find myself on the other side of the equation. Making sure that every result is water tight is the most important job of a convenor. When I am tasked with critiquing a result, I try to do so as nicely as I can, as I remember the other side very well.

My convenorship will be ending at the end of the year, and I’m looking forward to getting back to more technical work. I like making things that make people’s lives better and I really love hard technical problems. If somebody comes to me and says “nobody has ever figured out how to do this”, then that is all I will be able to think about for weeks. The more difficult the problem, the more interested I am.

Even simple things like, taking the figures and captions out of a paper automatically. This used to be a nightmare for ATLAS collaborators, as they had to do it manually and it could take hours. I developed a script to help me with this issue, and then shared it. It felt like a lifesaver to people and it developed into the figure processing script we use today throughout the collaboration.

The best advice I can give people trying to solve complex problems is to just... start. Being a good coder requires a certain mindset: you need to see the big problem, then look past it to start attacking the smaller problems inside of it that you know how to solve. And then rely on the fact that, when you get to the next small problem, you’ll know how to solve that too.

The next few years will be particularly busy for the ATLAS collaboration. First, we need to make absolute certain that if there are any new particles within our reach, we find them. Second, we need to consider the legacy we leave the physics community. Many of our measurements will serve the community for several decades, while we prepare for the next collider. Such was the case for LEP, whose direct stau production search we have only just recently managed to surpass. Our job now is to make sure that future colliders – be they the ILC or the FCC – will have to work just as hard to do the same to our results.

ATLAS Portraits is a new series of interviews presenting collaborators whose contributions have helped shape the ATLAS experiment. Look forward to further ATLAS Portraits in the coming months.

In conversation with Martine Bosman, a pioneer of ATLAS hadronic calorimetry

Steven Goldfarb — Mon, 26 Nov 2018 10:45:00 +0000

In conversation with Martine Bosman, a pioneer of ATLAS hadronic calorimetry

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Steven Goldfarb Mon, 26/11/2018 - 11:45

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Martine Bosman, outside her office in CERN's Building 40. (Image: E. Ward/ATLAS Collaboration)

A long-standing member of the ATLAS Collaboration, Martine Bosman is one of the pioneers behind the Tile Calorimeter. Over her long career with the Collaboration, she has held several key roles: from convenor of the Radiation Task Force and the Top Quark Group to Collaboration Board Chair. In this profile piece, Martine shares experiences and reflects on how the ATLAS Collaboration has grown and changed.

I joined ATLAS in 1993, shortly after moving to the Institute of High Energy Physics (IFAE) in Barcelona, Spain, where I still work today. At the time, the ATLAS Collaboration was still in the R&D phase. Several different proposals were being put forward for different sub-detectors and groups around the world were striving to prove that theirs was the best.

My group, led by Matteo Cavalli-Sforza, was working in calorimetry, in which I had no previous experience. My focus before had been in silicon vertex detectors and heavy flavour physics. It was a big change but, fortunately, I joined a very friendly team working in ATLAS right as the experiment was getting started!

Our goal was to build a sub-detector that could measure particle “jets” with the best possible resolution. These jets of particles would be created in abundance in LHC collisions. Our group was first part of the RD3 Collaboration, developing a calorimeter that used liquid argon, but soon joined the RD34 Collaboration where we could make a bigger impact.

The RD34 Collaboration proposed a design that used scintillating tiles oriented perpendicular to the beam, which was a new concept. At the time, we were competing with other R&D collaborations and, indeed, the hadronic barrel calorimeter could have been made with liquid argon technology like the rest of ATLAS’ calorimetry. We not only had to prove that our design could work, but also that it could be built at reasonable cost.

In the end, RD34’s design was chosen by ATLAS, as we were able to show that scintillator iron slices performed well, were easy to build and were the least expensive option. The RD34 design – now simply known as the ATLAS Tile Calorimeter – covers the most central region of the ATLAS experiment. It is composed of three large cylinders of 64 modules, each constructed of iron plates and plastic scintillator tiles oriented perpendicular to the beam.

1996 RD34 test beam: Marzio Nessi and Ilias Efthymiopoulos in front of the ATLAS Tile Calorimeter prototype at CERN. (Image: CERN)

Once the concept was approved, the next important step was to test our prototype detectors with beams. Our detector design was new and so there were still a number of open questions about how it would perform. For example, the placement of the scintillator tiles perpendicular to the beam meant that showers of particles could travel along the tiles. How would this affect the resolution? There were many parameters to adjust – such as the thickness of the scintillators and the iron plates, and the size of the cells – and we needed to verify the uniformity and stability of response.

We used beams in CERN’s North Area to demonstrate the Tile Calorimeter’s performance. It was a great place to work; RD34 was a very friendly collaboration and we had great picnics outside the experimental area.

When the ATLAS Collaboration started writing the sub-system Technical Design Reports (TDRs), I was one of the editors for calorimetry and jet response in the Detector and Physics Performance TDR. These were very intense but interesting times. This was when ATLAS changed from the mode of working on individual systems to start thinking about global performance. It required quite a change of mind set for the entire collaboration.

The work brought with it a number of logistical complications, especially as I had two very small children. This was in the time before videoconferencing, so when there was an important meeting at CERN I had to travel. In the mid-nineties, our family had to spend three months a year there. Even internet access was an issue. I remember, when we had all the deadlines for the TDR, my husband stayed with the kids at night while I was going to IFAE in order to get a good internet connection to do work!

In the years between the TDR publication and first collisions, I took on a number of different roles within ATLAS. I was one of the people responsible for the “Event Filter” of the trigger system, and convened the Radiation Task Force and the Top Quark Group. While each role presented unique challenges, the work was done by relatively small teams strongly dedicated to that subject. I think this is characteristic of the ATLAS Collaboration.

When collisions began, I think there was a real phase transition in the way we worked and in the level of stress. Once data started coming, it seemed as though the work would never stop – there was always something vital that needed to be done. This is still the case today, even though we are many years past first collisions!

Dealing with such demanding work can be tough for collaboration members. I approach problems by first trying to be well informed. I review the existing material and studies, and listen to people's opinions and ideas. It’s important to try to get the full picture before forming an opinion, otherwise you may end up attacking a problem from a too narrow perspective.

In 2013, while I was Collaboration Board Chair, ATLAS management setup a task force to ensure that the voices of our collaboration members are heard. Together with Howard Gordon and Beate Heinemann, we addressed the question of recognition of individual work in our big collaboration. Various measures were proposed and implemented, one of which was the establishment of the ATLAS Outstanding Achievement Awards. Today, there is still a lot of discussion inside the collaboration on how to deal with this complex problem, especially for young physicists. This is a process that continues and young people are taking a lot of initiatives. That is great.

All in all, being a part of the ATLAS Collaboration has meant being part of a community of achievers. I had the chance to live through the Higgs boson discovery time and be present in the CERN auditorium when the discovery was announced – a great moment. I now look forward to seeing what the next page of ATLAS history brings to science.

ATLAS Portraits is a new series of interviews presenting collaborators whose contributions have helped shape the ATLAS experiment. Look forward to further ATLAS Portraits in the coming months

In conversation with Nick Ellis, one of the architects of the ATLAS trigger

Steven Goldfarb — Sun, 10 Jun 2018 14:04:00 +0000

In conversation with Nick Ellis, one of the architects of the ATLAS trigger

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Steven Goldfarb Sun, 10/06/2018 - 16:04

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Nick Ellis with the ATLAS trigger system. (Image: K. Anthony/ATLAS Collaboration)

A long-standing member of the ATLAS Collaboration, CERN physicist Nick Ellis was one of the original architects of the ATLAS Trigger. Working in the 1980s and 1990s, Nick led groups developing innovative ways to move and process huge quantities of data for the next generation of colliders. It was a challenge some thought was impossible to meet. Nick currently leads the CERN ATLAS Trigger and Data Acquisition Group and shared his wealth of experience as a key part of the ATLAS Collaboration.

I first became involved in what was to become the ATLAS Collaboration in the mid- to late-1980s. I had been working on the UA1 experiment at CERN’s SPS proton–antiproton collider for several years on various physics analyses and also playing a leading role on the UA1 trigger.

People were starting to think about experiments for higher-energy machines, such as the Large Hadron Collider (LHC) and the never-completed Superconducting Super Collider (SSC). Of course, at this point there was no ATLAS or CMS or even the precursors. There were just groups of people getting together to discuss ideas.

I remember a first discussion I had about possibilities for the trigger in LHC experiments was over a coffee in CERN’s Restaurant 1 with Peter Jenni. He was on the UA2 experiment at the time and, together with a number of colleagues, was developing ideas for an LHC experiment. Peter later went on to lead the ATLAS Collaboration for over a decade. He told me that nobody was looking at how the trigger system might be designed, and he asked if I would like to develop something. So I did.

“At the time, we did not know that the future held so much possibility in terms of programmable logic. The early ideas for the first-level trigger were based on relatively primitive electronics: modules with discrete logic, memories and some custom integrated circuits.”

The ATLAS trigger is a multilevel system that selects events that are potentially interesting for physics studies from a much larger number of events. It is very challenging since we start off with an interaction rate of the order of a billion per second. In the first stage of the selection, that has to be done within a few millionths of a second, the event rate must be reduced to about 100 kHz, four orders of magnitude below to the interaction rate, i.e. only one in ten thousand collisions can give rise to a first-level trigger. Note that each event, corresponding to a given bunch crossing, contains many tens of interactions. The rate must then be brought down by a further two orders of magnitude before the data is recorded for offline analysis.

When I start working on such a complex technical problem, I sit down with a pen and paper and draw diagrams. It’s important to visualise the system. A trigger and data-acquisition system is complicated – you have data being produced, data being processed, data being moved. So, I make a sketch with arrows, writing down order of magnitude numbers, what has to talk to what, what signals have to be sent. These are very rough notes! I doubt anyone other than me would be able to read my sketches that fed into the early designs of ATLAS’ trigger.

Though I was specifically looking at the first-level calorimeter trigger, which was what I was working on at UA1, I was interested in the trigger more generally. At the time, we did not know that the future held so much possibility in terms of programmable logic. The early ideas for the first-level trigger were based on relatively primitive electronics: modules with discrete logic, memories and some custom integrated circuits.

There was also concern that the second-level trigger processing would be hard to implement, because those triggers would require too much data to move and too much data to process. Here, the first thing I had to do was to demonstrate that it could be done at all! I carried out an intellectual exercise to try and factorise the problem, to the maximal extent possible. I was driven to do this because it was so interesting, and it was virgin territory. There were no constraints on ideas that could be explored.

My initial studies were on a maximally-factorised model, the so-called “local–global scheme”. It was never my objective that one would necessarily implement this exact scheme, but I used it as the basis for brainstorming a region-of-interest (ROI) strategy for the trigger. The triggers would look at specified regions of the detector, identified by the first-level trigger, for features of interest, rather than trying to search for features everywhere in the event. This exercise demonstrated that, at any given point in the system, you could get the data movement and computation down to a manageable level.

The ATLAS Level-1 Calorimeter Trigger, located underground in a cavern adjacent to the experiment. (Image: K. Anthony/ATLAS Collaboration)

I, along with a few colleagues, developed this exercise into a study that we presented at the 1990 Large Hadron Collider workshop in Aachen, Germany. In the end, thanks to technological progress, it was not necessary to exploit all the ingredients used in the study. In more specific words, instead of separating the processing for each ROI and for each detector, we were able to use a single processor to process fully all of the ROIs in an event. The use of the first-level trigger to guide the second-level data access and processing became a key part of the ATLAS trigger philosophy.

In the years following the Aachen workshop, the ATLAS and CMS experiments began to take shape. It was a really exciting time, and the number of people involved was tiny in comparison to today. You could do anything and everything; you could come with completely new ideas!

When first beams and first collisions finally came, things went more smoothly than I had ever dared to hope. We had spent a lot of time planning for what would come when the first single beam came, when the first collisions came, what would we do, in what order, what might go wrong and how could we mitigate it. It has always been in my nature to think ahead about all the potential problems and make plans that let us avoid future issues, ensuring that systems are robust so that a local problem does not become a global problem. Thanks to the work of excellent, dedicated colleagues, everything went really well for first collisions!

Clearly ATLAS has a long future ahead of it, although we will always face challenges: the upgrades we have planned are by no means trivial! Even with our existing infrastructure and experience, there will no doubt be obstacles that we will have to overcome.

And, of course, in the even longer term, CERN itself could change, depending on what happens in physics and on the global stage. It wouldn’t be the first laboratory to do so – just look at DESY and SLAC. Even Fermilab has changed from a collider to a neutrino facility. We never know where the next big discovery will lead us!

ATLAS Portraits is a new series of interviews presenting collaborators whose contributions have helped shape the ATLAS experiment. Look forward to further ATLAS Portraits in the coming months