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INTERVIEW
Nicolas Arnaud, who are you?
I am a physicist at the Linear Accelerator Laboratory (LAL), a joint research unit of the CNRS and Université Paris-Sud 11. LAL is part of the National Institute of Nuclear Physics and Particle Physics (IN2P3, one of the ten institutes of the CNRS), established in 1971. You are a researcher in particle physics and you work on an experiment called BaBar. What is it?
It is an international collaboration whose goal is to study B mesons and their B bar anti-particles (“B” + "B bar" becomes "BaBar"). The detector recorded data between 1999 and 2008 at the SLAC National Accelerator Laboratory in California (one of the largest U.S. high energy physics laboratories). This is a "precision" experiment for which the aim was to produce a maximum of data in order to thoroughly test the Standard Model of particle physics. The Standard Model is the theory with which it is possible to describe and link the different elementary components of matter with the weak, strong and electromagnetic forces. The objective has been achieved in particular with the experimental confirmation of the validity of the "CKM" matrix on the mixing of quarks, named after the name of its "inventors" Cabibbo, Kobayashi and Maskawa. A quark is an elementary component of matter, that is to say, we cannot divide it. In fact, BaBar has published many results in various fields and the data analysis is expected to continue for several years. You can find more information BaBar’s public page: http://www-public.slac.stanford.edu/babar
What is your role in this experiment?
My activities in BaBar were focused mainly on the detector; I was posted at SLAC for 4 years from 2005 to 2008. My task was to participate in maintenance operations, anticipate potential failures, repair them if necessary and maintain the highest possible usable BaBar cycle: 97-98% of beamtime for many years. I also worked on the quality of data processing between the detector where they are recorded and the physicists’ computers where they were analyzed. I also participated in data analysis and I was responsible for BaBar in my laboratory.
The BaBar experiment has come to an end. What are your new projects?
I work primarily on the SuperB project: this is a new-generation experiment, similar in principle to BaBar, but whose goal is to collect a hundred times more data in order to make more accurate measurements and search for rare phenomena such as manifestations of "violation of CP symmetry, that is to say, differences between particles of matter and antimatter. SuperB is funded mainly by Italy (with significant involvement of American and European laboratories, especially French) whose government has repeatedly indicated its interest in this project. However, the current situation (both economic and political) has delayed the official green light and the release of initial funds. Currently the teams involved are working on preparing the "Technical Design Report” of the detector, a very detailed report to prove the feasibility of the apparatus and show that the very ambitious physics goals can be achieved. .At LAL we therefore carry out simulations on the detector and conduct research and development in detection methods, instruments, electronics, etc.. The storage ring should be about 1.5 kilometers in circumference, a respectable size but much lower than the LHC collider at CERN. The size difference is explained primarily by the beam energy, approximately one thousand times lower than that achieved at CERN: the more energetic the particles, the less they can turn easily. As with BaBar, the nominal collision energy at SuperB is set to produce the maximum of B and B bar mesons.
How are you connected to SOLEIL?
Particles lose energy in the form of synchrotron radiation in colliders such as LHC, BaBar, etc. as well as in instruments such as SOLEIL. Whether working on high energy physics or on SOLEIL, synchrotron radiation is a factor that needs to be taken into account and offset (energy must be continuously supplied to the particles to compensate for these losses). In the first case, it's just stray radiation, whereas it is at the heart of the process in the second. So there are strong links between high-energy physics and the world of synchrotrons. More specifically, the LAL has contributed greatly to the development of the first collider and initiating the scientific use of synchrotron radiation in the years 1960-1970. In addition, SOLEIL may be seen as a continuation of LURE ("Laboratory for the Use of Electromagnetic Radiation"), a LAL laboratory in the 1980s. For all these reasons, LAL (for which I am co-responsible for communication with Helen Kerec), supports, as does SOLEIL, the Sciences-ACO Association, located on the Orsay campus of Paris-Sud University, and preserves “l’Anneau de Collisions d'Orsay” (ACO), an instrument of great historical value, both in the development of accelerators and in the use of synchrotron radiation, the area where SOLEIL is at the forefront. ACO, open to the public by appointment and during national events such as the science festival, is included in the supplementary inventory of historical monuments. For more information see: http://sciences-aco.lal.in2p3.fr
What made you want to speak in front of a group of teachers?
My perpetual wish, but never realized, to overcome my natural timidity!
Seriously, I've always been attracted by the popularization of science for the general public and schools; I try to devote some of my time to it, in addition to my research work. I find these two activities complementary and in my mind they are an integral part of my job.
So, I have participated since 2003 in writing the review "Elémentaire" which has published eight issues on particle physics, from the atom to approaches for going beyond the Standard Model (the current theory on the "infinitely small ") including, of course, the LHC, the largest project in the field. All issues are downloadable in pdf format on the website(http://elementaire.web.lal.in2p3.fr).
More recently, I was on the editorial board of the book, called "Passport pour les deux infinis" to which more than fifty people from the CNRS, CEA and universities contributed. This is a reversible work (!) that guides the reader to the "infinitely small" (the world of particles) in one direction and towards the "infinitely large" (the universe) in the other. The articles are short (2 pages), written for the general public and require just a high school level of scientific literacy. One of them, written by Marie-Pauline Gacoin, in fact covers synchrotron radiation and SOLEIL. In each run, the first articles cover the most important concepts in the field, followed by descriptions of experiments that are currently studying them. Finally, there are glossaries explaining the "complicated" terms encountered in the various articles. The book has just been published by Dunod and teachers who request it via the website http://www.passeport2i.fr can receive a free copy.
Moreover, the "Passport pour les deux infinis" is a comprehensive educational project that goes far beyond the book: other aspects are described on the website, still under construction.
What are the connections between your work, SOLEIL and the LHC at CERN?
The main point they have in common is that all these projects use accelerators! The LHC is the current big project in particle physics, both by the size of the equipment, the number of people who work there, the physics goals and the expectations of the scientific community as a whole! LAL has always been very involved in the experiments at CERN for the last 50 years or so, but the LHC is not the only interesting experiment for our community and it is normal that other detectors are also currently operating or being planned: SuperB, experiments on neutrinos and cosmic radiation, the Planck satellite, which is studying the "First Light of the Universe", gravitational wave detectors such as Virgo, etc..
As for SOLEIL, it is an essential application of accelerator physics and is very useful for many sciences: materials, biology, medicine, etc. It would really have been a shame not to build this instrument and I am very happy to work "in the shadow" of SOLEIL, on the Saclay campus in the Chevreuse valley! |
