Heavy quark production from Color Glass Condensate at RHIC

I consider production of heavy quarks in pA and AA collisions in the framework of the Color Glass Condensate. I discuss the heavy quark production in pA collisions in a classical approximation which takes into account all multiple rescatterings of a proton in a nucleus. For peripheral collisions, heavy quark production cross section can be written in kT -factorized form. The kT factorization is used to construct a simple model which takes into account both classical and quantum effects in pA and AA collisions. I review the main result of calculation based on that model: open charm in the central rapidity region at RHIC gets suppressed as a function of rapidity. Although the numbers obtained for the suppression factor are model dependent, the very fact of suppression is the general feature of the Color Glass Condensate at RHIC kinematical region. It indicates the onset of quantum evolution effects in a nucleus and is universal for all inclusive processes. The process of heavy quark production in pA collisions at high energies has three separated in time stages in the nucleus rest frame. Emission of a gluon g by a proton’s valence quark qv takes much longer time τqv→qvg than a subsequent emission of a qq̄ pair by a gluon tg→qq̄ ≪ τqv→qvg. In turn, the time of interaction of a qvgqq̄ system with a nucleus is of the order of nuclear length RA and is negligible as compared to the evolution time of the proton wave function τqv→qvg ≫ tg→qq̄ ≫ RA. For example, the gluon emission takes time τqv→qg ≈ 2q q2 = 1 xMN ≫ RA ≃ τint, (1) where the proton is moving in + light-cone direction. The same argument applies to the successive emission of a quark-antiquark pair by a gluon in a proton’s wave function. The separation of times is ensured by strong ordering q ≫ k ≫ kT , where k and kT are the quark energy and transverse momentum respectively. Therefore, processes in which gluon or heavy quarks are produced in course of the rescatterings in a nucleus are suppressed by powers of energy p [1]. As the result, the differential cross section for the quark production can be written in a factorized form as a convolution of the valence quark and gluon wave functions with the rescattering factor. The final results takes form [2, 3, 4] dσ d2k dy = ∫