mardi 22 octobre 2013 à 17:00
Amphi G. Besse
In the framework of perturbative quantum chromodynamics I study the effect of parton energy loss in cold nuclear matter on the nuclear attenuation of quarkonium production in proton-nucleus (p-A) collisions.
The first part of the study is devoted to the derivation of parton energy loss in various kinematical situations. In particular, special attention is paid to the case of an energetic parton crossing a nuclear target and being scattered to small angle. In this case the radiative energy loss is shown to be proportional to the parton energy, which may have crucial consequences on phenomenology. Indeed, at high energy and not too low xF, quarkonium production in p-A collisions can be described, at the partonic level, as the propagation of a color octet heavy quark-antiquark pair through the target, losing energy as a gluon.
In a second part, I develop a phenomenological model to study the effect of such energy loss on J/psi nuclear suppression. The main assumption of the model is to express the xF-differential J/psi cross section in p-A collisions simply as that in p-p, with a shift in xF accounting for the energy loss through the nucleus. The model is then generalized to implement the Cronin effect, by taking into account the shift in pT due to transverse momentum broadening in the nucleus. The comparison between the model and the experimental data for J/psi nuclear suppression at various collision energies and for various nuclei appears to be very satisfactory.