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

30 January 2024 | By

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).

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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.