I am a particle physicist involved in flavour physics. Flavour physics studies the interactions, and mostly the decays, of particles made of quarks, the constituents of protons and neutrons. I am especially working on the decays of the b quark, a quark 5 times as heavy as a proton and which is unstable, with a mean lifetime of about a picosecond.
We are actually not so much interested in the quarks themselves, but more in the interactions that occur when these quark decay. These decays involve well-known particles like the W, the mediator of the nuclear weak interaction. But they could as well involve particles we have not yet discovered. Untypical decays of the b quark could provide indirect evidence for not yet observed particles.
This is the reason I am especially working on so-called "penguin" decays, decays that involve a loop made of two mediator particles. These decays are so rare that the "new" particles could potentially contribute significantly to the decay. There are many reasons for looking for new particles. Presently all particles we know are described by a theory called the "Standard Model" of particle physics. It's a very accurate theory that allows precise predictions but it is theoretically unsatisfactory. For example it does not involve gravity and cannot describe the conditions that lead to the formation of the universe. This is why many extensions of the Standard Model are proposed, all of them having one common feature: they predict the existance of yet unobserved heavy particles. Such particles could be observed directly by producing them in high-energy collisions, or indirectly by looking for discrepancies between the Standard Model predictions of decay rates and experimental measurements.
I am presently involved in the LHCb experiment that will start taking data in 2007 at the new largest accelerator in the world, the LHC, near Geneva. The Imperial College LHCb group will mainly study the decay of the B meson (a particle containing a b quark) to the K* meson and two muons. This is the best candidate for observing effects not predicted by the Standard Model.
Presently I am contributing to the preparation of the analysis software that needs to be ready by 2007. Computing is a big challenge in all LHC experiments. We will have mountains of data to analyse. CERN is leading the effort in developing new tools for this task, just like it invented the web 15 years ago.
Before I came to LHCb I was active on the Belle experiment in Tsukuba, Japan. There I measured the decay rate of the B meson to a photon and anything else. This is also a penguin decay. But no discrepancy between the Standard Model and the experiment could be observed, which sets very strong constraints on any theory trying to extend the Standard Model.
See also:
- A longer description of penguin decays, involving elephants and rabbits.
- My talks at conferences.
- My private website with many pictures and a blog (in french) about my life in Japan.
