A–dependence in dilepton rapidity distributions: parton model and dipole approach analysis

We calculate dilepton production cross section at RHIC using the improved parton model and color dipole approach in p–A collisions at backward rapidities. Our results are given as nuclear modification factors. We test three nuclear parton distribution functions: EKS, EPS08 and EPS09; we found no changes in the results. In the color dipole approach, we use GBW, DHJ, and BUW color dipole cross section models; again, no relevant difference is found in the nuclear modification factor, in spite of that DHJ breaks geometric scaling and that the p–p cross sections show relevant differences. The presence of intrinsic transverse momentum in the improved parton model is investigated, showing that nuclear effects are sensitive to this assumption. The color dipole approach lacks this intrinsic kT and thus nuclear effects can discriminate among both analysis. We extend our improved parton model results to forward rapidities and compare with CGC results, obtaining agreement between the models.