xF dependence of the Drell-Yan transverse momentum broadening

We analyze xF dependence of the Drell-Yan transverse momentum broadening in hadron-nucleus collisions. In terms of generalized factorization theorem, we show that the xF dependence of the transverse momentum broadening, ∆〈q2 T 〉(xF ), can be calculated in perturbative QCD. We demonstrate that ∆〈q2 T 〉(xF ) is a good observable for studying the effects of initial-state multiple scattering and extracting quark-gluon correlation functions. 13.85.Qk, 12.38.Bx, 11.80.La, 24.85.+p Typeset using REVTEX Email: [email protected] 1 Parton multiple scattering is responsible for many interesting and important phenomena in high energy collisions involving nucleus, such as transverse momentum broadening, energy loss, as well as the nuclear suppression of quarkonium states. Understanding the mechanism of parton multiple scattering and its effects is crucial for making precise predictions of the nuclear suppression of quarkonium productions, which maybe a potential signal for the quark-gluon plasma in relativistic heavy ion collisions [1]. Parton multiple scattering can happen both at the initial state or at the final state. The Drell-Yan pair production in hadron-nucleus collisions provide an excellent place to study effects of initial state parton multiple scattering. The nuclear dependence in the Drell-Yan transverse momentum spectrum for the large qT region has been studied in QCD perturbation theory [2,3]. In terms of generalized factorization theorem in QCD [4], the effects of multiple scattering can be expressed in terms of multiparton correlation functions [5], which are as fundamental as the parton distributions. However, these parton correlation functions are not well determined yet. In this letter, we derive the xF dependence of the Drell-Yan transverse momentum broadening. We show that ∆〈q2 T 〉(xF ) can be used as a good observable to study the effects of initial-state multiple scattering and parton energy loss. In addition, it can be used as an excellent observable for extracting information on multi-parton correlation functions. Consider the Drell-Yan process in hadron-nucleus collisions, h(p)+A(p) → ll(q)+X, where q is the four-momentum for the virtual photon γ which decays into the lepton pair. p is the momentum for the incoming beam hadron and p is the momentum per nucleon for the nucleus with the atomic number A. Let qT be the transverse momentum of the Drell-Yan pair, we define the averaged transverse momentum square as 〈q T 〉 = ∫ dq T · q T · dσhA dQ2dq T /