High density effects in the dilepton production in cosmic ray interactions

Abstract

Particles coming from the space reach our atmosphere at all moment and could come with extremely high energy of orders of 1020 eV and because of this are called Ultra High Energy Cosmic Rays (UHECR). The interaction of the UHECR with the atmosphere produce extended cosmics rays air showers. In particular, pair of leptons (dileptons) are produced in this interaction. Consequently, the evaluation of the dilepton production cross section can be useful to study the strong interactions at extreme energies, where parton saturation effects, associated to the high parton density, are expected to be present. In this work we investigate the implications of the these effects in the Drell-Yan process. The dipole approach is used as the theoretical framework for calculation of cross sections. In this formalism, the interaction between projectile and target is described by the dipole cross section σdip. A comparison between the models of σdip proposed by Golec-Biernat and Wüsthoff (GBW) and Albacete et al. (rcBK), that describe the physics of partonic saturation, are performed. For comparison, we calculate the cross section for dilepton production using the first order expansion in the GBW, where saturation effects are not present. Our results demonstrate that the high density effects are very large (≥102) at small transverse momentum and UHECR energies.