Over the coming weeks, the ‘In Practice’ series of articles will get you up close and personal with experimental physicists – the people who build the LHC experiments. These scientists use complex instruments to test theories that first appeared long-ago on a blackboard. But who are they? How do they build their fantastic tools? How do they actually practice physics? How do they view the future of their field? The first in our ‘In Practice’ series turns the spotlight on particle physics’ flagship projects and their builders.
Enter the lift and hit the -1 button. In a few seconds you are whisked 100 metres below the Earth's surface. Take one of the winding corridors that lead to the experimental cavern. Now, push back the heavy metal door, hold your breath and open your eyes wide.
Towering above you is a remarkable edifice of steel and cables, a sophisticated, one-of-a-kind assembly of millions of fragile components, winking in the glare of the floodlights above.
“When I first came to CERN, I was a student, dreaming of becoming a physicist,” says Barbara Storaci, Operation Coordinator for the LHCb experiment. “I visited one of the LHC experimental caverns and was simply blown away. My dream had finally taken physical shape, it was amazing!” A few years later, a fully-fledged physicist, Barbara was installing cables at the LHCb detector.
“I feel the same excitement every time I go in the experimental cavern. I know I’ve made my own small contribution to this extraordinary endeavour.” - Barbara Storaci
All the physicists at the LHC experiments share the same feelings of pride and admiration about their gigantic detectors. This feeling of wonder never fades.
It all started on a blackboard
Particle physicists are like architects and builders. They knew that no vehicle existed to transport them to the outer reaches of physics, so they had to invent their own space-ship. It all began with an idea, like a blueprint, on a theorist’s blackboard. “The most inspiring thing for me is that you imagine and build an entire experiment to test a theory,” says CMS physicist, Nadjieh Jafari. “The CMS muon system was designed to discover the Higgs boson, but at the moment of designing it the Higgs boson was just an idea. And then we actually found it. For me that’s absolutely beautiful!”
It took collaborations of thousands of scientists several decades to design, develop, test, assemble, calibrate and commission these instruments. “It’s the work of a whole generation,” observes LHCb physicist Sneha Malde. Armies of physicists, technicians, operators and students from all countries and all fields contributed to the work. Nadjieh adds: “The amazing fact is that thousands of pieces of sub-detectors, built in many labs in the world, are one day assembled together in an experimental cavern at CERN, and they work perfectly together as a single detector.”
Exploration of the infinitesimally small, like space exploration for the infinitely big, pushes technology to its limits. Technicians and engineers have many a tale to tell about how this or that physicist asked them to achieve the impossible for their future detector: non-existent components, non-standard specifications, unprecedented levels of precision. Their ingeniousness often won the day, and that’s how particle physics manages to push back the frontiers of technology.
“I have great respect for the contribution of technicians to experimental physics. You could say they are the unsung heroes of our field,” - David Francis, responsible for the trigger and data acquisition systems of the ATLAS experiment.
Curiosity and determination
But it wasn’t the lure of these high-tech instruments that attracted the physicists into the field. Their vocation was nourished by an insatiable desire to understand the hidden workings of the universe. But when you think about the universe, you picture stars, not particles. So many of them first turned their gaze towards astroparticle physics or astronomy before changing direction. “I felt like I was collecting stars as if they were stamps,” says Patrick Koppenburg of the LHCb experiment.
“After three years of astronomy at university, I took a course in particle physics,” says Manuela Venturi of the ATLAS experiment. “It seemed like this discipline lets us go beyond mere observation and explains how and why things work.”
Many career paths exist, but you don’t just stumble into a career in particle physics by chance. The learning curve is steep and the obstacles numerous, so anyone who manages to build a career must be armed with rock-solid determination. A qualified accountant, LHCb physicist Sneha Malde stepped out of a comfortable, well-defined career to tread the uncertain path of particle physics, and managed to get a doctoral bursary at Oxford. “I recently asked my thesis supervisor why he recruited me and he said it’s because you left and wanted to come back. I knew that you were determined to come back and I could see that in your face. That’s why I offered you a position.”
Patrick Robbe, LHCb Run Coordinator, graduated from one of France’s most prestigious engineering schools, which opens up attractive career opportunities in the upper echelons of the civil service or industry. Some of his fellow alumni walked into top jobs, or at least jobs that are much better paid than in France’s public research sector. “But I don’t envy them because my work is so interesting,” he remarks.
But it’s the radiant Barbara Storaci who wins the prize for being the most opinionated. When she was just 11 years old, her curiosity was tweaked by a half-baked explanation given to her class by her physics teacher. This spurred her to devote her reading time, her studies and eventually her life to particle physics. “I have always wanted to work in particle physics. My dream was to come to CERN and I have devoted my life to fulfilling that dream,” she states.
But once you’ve arrived, you’re still not quite there yet. No matter how impassioned and tenacious young physicists may be, posts are like gold-dust.
Hierarchy and democracy
It’s Tuesday, 2pm, in the Dirac meeting room in one of CERN’s LHC experiment buildings. Every week, the ATLAS collaboration holds its plenary meetings here on the same day, at the same time. The room is packed to the rafters, but only contains a small fraction of the collaboration and its 2500 (and growing) members. Most have tuned in remotely from their institute to hear the latest news. These meetings are essential to maintaining the cohesion of the experiment. In fact, each of the major collaborations organises dozens of meetings like this to coordinate the projects and their analyses. “A few too many meetings,” some say under their breath. But managing thousands of collaboration members, who work for dozens of institutes across the globe, is no mean feat.
The experiment’s ‘leader’ (known as the spokesperson) is not their line manager because they work for, and are accountable to, an institute. Here the hierarchy is flat and democracy is the name of the game. The spokesperson and the other main leaders are elected, usually for two years. Group coordinators are appointed, but often through a consensus-driven selection process, also for limited durations. When they leave office, they all go back to being ‘normal physicists’ once more. This is an unusual way of operating in a work environment where hierarchical structures are generally far more heavy. Indeed, these large scientific collaborations are cited as examples by sociologists the world over. “It’s hard to believe, but it does work. Mainly because we all have the same objective, physics,” explains David Francis.
“It works because scientists are so enthusiastic and keen to keep the project alive, but it’s a very singular dynamic, founded on intellectual merit rather than hierarchy,” - Barbara Storaci
The scientists could be forgiven for feeling a bit lost in such a crowd of like-minded people. But the unprecedented energy levels of the LHC give them all a unique opportunity to explore uncharted territory. “What motivates us in these large experiments is taking part in completely new science, to tread where no-one has trodden before,” explains Siegfried Foertsch of the ALICE experiment.
The challenge of operating such sophisticated detectors and of pushing back the frontiers of knowledge is what binds the collaborations together. “We’re united by our common goal and passion for physics,” Barbara concludes.