Nuclear effects in Drell-Yan pair production in high-energypAcollisions

Abstract

The Drell-Yan (DY) process of dilepton pair production off nuclei is not affected by final state interactions, energy loss or absorption. A detailed phenomenological study of this process is thus convenient for investigation of the onset of initial-state effects in proton-nucleus (pA) collisions. In this paper, we present a comprehensive analysis of the DY process in pA interactions at RHIC and LHC energies in the color dipole framework. We analyse several effects affecting the nuclear suppression, RpA < 1, of dilepton pairs, such as the saturation effects, restrictions imposed by energy conservation (the initial-state effective energy loss) and the gluon shadowing, as a function of the rapidity, invariant mass of dileptons and their transverse momenta pT . In this analysis, we take into account besides the γ * also the Z 0 contribution to the production cross section, thus extending the predictions to large dilepton invariant masses. Besides the nuclear attenuation of produced dileptons at large energies and forward rapidities emerging due to the onset of shadowing effects, we predict a strong suppression at large pT , dilepton invariant masses and Feynman xF caused by the Initial State Interaction effects in kinematic regions where no shadowing is expected. The manifestations of nuclear effects are investigated also in terms of the correlation function in azimuthal angle between the dilepton pair and a forward pion ∆φ for different energies, dilepton rapidites and invariant dilepton masses. We predict that the characteristic double-peak structure of the correlation function around ∆φ ≃ π arises for very forward pions and large-mass dilepton pairs.

Phenomenological Review on Quark–Gluon Plasma: Concepts vs. Observations

“…[246][247][248][249][250][251][252]). In heavy-ion collisions at high energies, due to the absence of final state interactions, the DY pair production process on nuclear targets in the dipole picture is often considered to be an excellent probe accessing the impact parameter dependence of the Initial State Interaction (ISI) effects as well as nuclear shadowing and nuclear broadening-the crucial information that cannot be derived within the parton model (e.g., [253][254][255] and references therein). The ISI effects emerging due to multiple rescattering of projectile partons in a medium prior to a hard scattering are only relevant close to kinematic boundaries due to energy conservation significantly suppressing the nuclear cross-sections [256,257]; e.g., when the Feynman variable…”

“…In Ref. [254], it was noticed that the long coherence length (LCL) compared to the nuclear radius R A (namely, l c R A ) is practically useful in kinematic domains of RHIC and the LHC experiments. The quark shadowing in the LCL limit is automatically accounted for by scattering of the leading Fock components in the dipole formula which represents a process-dependent convolution of the light-cone wave function for a given Fock state with a superposition of partial dipole amplitudes.…”

Nuclear modification of forward Drell-Yan production at the LHC

“…The study of the Drell-Yan process in the color dipole approach has been the subject of many theoretical and phenomenological works, see for example Refs. [6][7][8][9][10][11][12][13][14][15][16][17][18][19]. In this formalism, the physical picture is the following: a collinear quark emitted by the projectile proton can radiate a virtual photon either before or after interacting with the dense color field of the target.…”

Drell-Yan process at the LHC in p+Pb collisions

“…It was demonstrated in Ref. [3] that the coherence length is larger than the nuclear radius l c R A for the LHC kinematics, and, therefore, the long coherence length (LCL) limit can be safely used. Otherwise, the universal Green function formalism should be employed to account for finite l c effects [4].…”