The ATLAS inner tracker and the detection of light super-symmetric Higgs boson
Promotion date: 1 October 2003
The Centre Européen de Physique Nucléaire (CERN) is building the Large Hadron Collider (LHC) with a total length of 27 kms. It is to accelerate two proton beams in opposite directions to an unprecedented energy of 7 TeV. This international effort is made in order to verify the validity of the Standard Model that describes the laws governing the smallest particles (quarks), or to encounter new non-standard physics. Marcel Vos is part of this mind boggling world.
What is your connection with the Mesa+ Institute?
“The link between the high energy physics and the Mesa+ Institute are the superconductor magnets deflecting the particle beams in the accelerator and providing the momentum measurement in the detector. Herman ten Kate of low temperatures in particular is involved in this. But the larger part of my research was done in Spain at the Instituto de Física Corpuscular. Consultations with my promotor Bob van Eijk were usually held at the Nederlands Instituut voor Kern- en Hoge Energie Fysica (NIKHEF) in Amsterdam.
I understand that 2000 people from various nationalities are working on this scientific project. How did you get in?
The high energy physics world is very international; there are only two large facilities in the world. The LHC is being built in Geneva and there is another big accelerator in the US. When I finished at Utrecht University I wanted the international experience and I sent some application letters to various institutes involved in this line of research. I was accepted in Spain.
What is your part in this project?
I am part of the ATLAS collaboration, building a detector at one of the four interaction points where the two proton beams collide in LHC. This detector is an enormous thing about the size of a five floor building. In each interaction point large experimental facilities are built to study the result of each collision. IFIC Valencia, where I spent the larger part of my studies, produces a certain percentage of the inner layer elements detecting charged particles in the detector. They are being designed at universities and subsequently industrially produced. These elements are put together into a module and thoroughly tested, because after we have installed it in the detector we cannot get at it anymore. So everything has to function properly. My job is to take these modules to Geneva and to test and evaluate their functioning in a particle beam in another of CERN accelerators.
We use simulation programmes to predict the performance of our detector in several physics scenarios. Much of this effort is focused on the detection of the Higgs field, the existence of which has never been proven experimentally. In my thesis I investigate a special case: the possibility to discover super-symmetric Higgs bosons through their decay to muons.
The ATLAS detector is sensitive to signals from both over a large energy range. If no evidence of the Higgs boson is found in this detector, the theoretical people had better put up their thinking caps once more.
What about the energy aspect, are you involved in that at all?
No, our research is not aimed at finding new energy resources, but of course that may eventually happen. When we get a better understanding of the fundamental theory we increase our chances of eventually finding something in the way of our dream of a clean unlimited energy source.
How does it feel to only work at such a small part of such a major project?
Well, of course working with five persons on a limited experiment is quicker. But all the minor experiments in this field have been done already. A machine this size requires a big scientific group, which in one way functions as a kind of multinational - lots of meetings and slow decisions. In another way it does not because there is no hierarchy between experimental groups. Nobody is pushed into a certain direction by a central governing body. There are spokespersons of every group keeping the others informed of what they are doing and they are in practice responsible for time planning and quality. It is rather unique to work in such an Athenian democracy. The outcome of this project is a matter of generations. You will have to think in small steps and be happy with that. There is challenge enough.
You live in Pisa now?
Yes, I received a 2,5 year grant from the European Union. What will happen after that is yet uncertain. On the one hand you can work everywhere in the western world, on the other: I have a family now and moving every 3 or 5 years disrupts the life of children. We’ll have to see. There is a fair chance of getting a permanent position when you have built on your curriculum with a number of publications and post-docs. But it is a competitive world. That is why many physicists look for a job in IT when they graduate from university. Many of my friends earn a packet now. If you find money important, a scientific career in physics is no option.”