Emmanuel Gräve de Oliveira

Dilepton distributions at backward rapidities

The dilepton production at backward rapidities in pAu and pp collisions at RHIC and LHC energies is investigated in the dipole approach. The results are shown through the nuclear modification ratio R{sub pA} considering transverse momentum and rapidity spectra. The dilepton modification ratio presents interesting behavior at the backward rapidities when compared with the already known forward ones, since it is related with the large x kinematical region that is being probed. The rapidity dependence of the nuclear modification ratio in the dilepton production is strongly dependent on the Bjorken x behavior of the nuclear structure function ratio R{sub F{sub 2}}=F{sub 2}{sup A}/F{sub 2}{sup p}. The R{sub pA} transverse momentum dependence at backward rapidities is modified due to the large x nuclear effects: at RHIC energies, for instance, the ratio R{sub pA} is reduced as p{sub T} increases, presenting an opposite behavior when compared with the forward one. It implies that the dilepton production at backward rapidities should carry information of the nuclear effects at large Bjorken x, as well as that it is useful to investigate the p{sub T} dependence of the observables in this kinematical regime.

Confronting color dipole and intrinsic kT approaches in D-Y dilepton production

We study the Drell-Yan dilepton production in proton-nucleus collisions at RHIC energies. We use two different approaches: the usual intrinsic transverse momentum approach at NLO in the infinitum momentum frame; and the color dipole in the target rest frame. We compare both formalisms at backward rapidities (proton as a target). At forward rapidities, we use earlier results considering the nucleus in a Color Glass Condensate phase. We show qualitative agreement between the two formalisms through the nuclear modification ratio as a function of both rapidity and transverse momentum and that low-mass dileptons are relevant observables to probe nuclear effects.

BACKWARD RAPIDITY DISTRIBUTIONS IN COLOR DIPOLE MODEL

The color dipole model is traditionally applied to forward rapidities. Alternatively, we employ the dipole model to obtain backward rapidity distributions. We have chosen to work with dilepton production in pAu and pp collisions at RHIC and LHC energies. The results are best understood with the help of a nuclear modification factor RpA as a function of transverse momentum and of rapidity. As it is found, dilepton production at backward rapidities is very dependent on nuclear effects.