Parton energy loss and modified beam quark distribution functions in Drell–Yan process in collisions

Abstract

Within the framework of generalized collinear factorization in perturbative QCD (pQCD), we study the effect of initial multiple parton scattering and induced parton energy loss in DrellYan (DY) process in proton-nucleus collisions. We express the contribution from multiple parton scattering and induced gluon radiation to the DY dilepton spectra in terms of nuclear modified effective beam quark distribution functions. The modification depends on the quark transport parameter in nuclear medium. This is similar to the final-state multiple parton scattering in deeply inelastic scattering (DIS) off large nuclei and leads to the suppression of the Drell-Yan cross section in p + A relative to p + p collisions. With the value of quark transport parameter determined from the nuclear modification of single-inclusive DIS hadron spectra as measured by the HERMES experiment, we calculate DY spectra in p + A collisions and find the nuclear suppression due to beam parton energy loss negligible at the Fermilab energy E lab =800 GeV in the kinematic region as covered by the E866 experiment. Most of the observed nuclear suppression of DY spectra in E866 experiment can be described well by parton shadowing in target nuclei as given by the EPS08 parameterization. The effect of beam parton energy loss, however, becomes significant for DY lepton pairs with large beam parton momentum fraction x ′ or small target parton momentum fraction x. We also predict the DY cross section in p + A collisions at lower beam proton energy E lab =120 GeV and show significant suppression due to initial state parton energy loss at moderately large x ′ where the effect of parton shadowing is very small.

Initial conditions for the modified evolution of fragmentation functions in the nuclear medium

“…The higher-twist corrections can be expressed in terms of medium modified parton fragmentation function [12,13,27,28]. Such an approach to parton energy loss through medium modified fragmentation functions (mFF's) has been employed to describe suppression of leading hadrons in DIS, nuclear modification of Drell-Yan spectra in p+A collisions [29] as well as jet quenching in high-energy heavy-ion collisions [30][31][32][33][34]. In this description of parton energy loss with single gluon emission, medium corrections to the fragmentation functions can become large enough ( long propagation length in very dense medium) to make the modified fragmentation functions (vacuum + medium correction) negative at large fractional momentum z.…”

Effects of cold nuclear matter energy loss on inclusive jet production inp+Acollisions at energies available at the BNL Relativistic Heavy Ion Collider and the CERN Large Hadron Collider

“…In p+A collisions, the production yield of single inclusive jets is affected by a number of CNM effects, all of which have clear physical/dynamical origin, mostly centered around the idea of multiple parton scattering. They include dynamical nuclear shadowing [15,16], Cronin effect [17,18], incoherent multiple scattering [19,20] and CNM energy loss [21][22][23][24][25][26][27][28][29], which can all be calculated from the elastic, inelastic and coherent scattering processes of partons in large nuclei [30][31][32][33][34]. It was found in our previous studies that dynamical shadowing, incoherent multiple scattering as well as Cronin effects play important roles only in the small and intermediate transverse momentum regions [32].…”

Medium-induced soft gluon radiation in forward dijet production in relativistic proton-nucleus collisions

“…First, the leftmost inequality is equivalent to saying that at the time t f ∼ ω/k 2 ⊥ of its emission, the soft gluon does not probe the relative displacement ∆ r of the core charge 4 The result (2.8) (L ≫ λg) could have been guessed from the result (2.7) (L ≪ λg) using heuristic arguments. In the case L ≪ λg, the prefactor L/λg in (2.7) can be interpreted as a (small) rescattering probability.…”

“…For example, the effects due to initial and final state radiation in hadron and Drell-Yan production at forward rapidity in p-A (or d-A) collisions have been studied, in particular in refs. [2][3][4].…”