Light-front imaging of composite particles

Wednesday 7 Dec 2011, 14:00 → 15:00 Europe/Paris

Room 149 (LPSC)

The LHC collides protons at very high energy with the hope of discovering the Higgs particle and maybe signs of new physics beyond the Standard Model like e.g. supersymmetry. Since at those energies the process is dominated by the scattering at the elementary level, it is important to understand how partons, i.e. quarks and gluons, are distributed inside the proton. This distribution falls in the non-perturbative regime of QCD and cannot be determined accurately from first principles. Using Lorentz, parity, time-reversal and gauge symmetries, one can parametrize our ignorance and introduce parton distribution functions. These functions are universal in the sense that once extracted from some process, they can be used in other processes to make predictions. They are also interesting on their own since they provide an imaging of composite particles in the infinite momentum frame. This semi-classical picture allows one to study in particular the orbital angular momentum and leads to a criterion regarding the composite nature of a particle with any spin.