Drell-Yan process in pA collisions: Path-integral treatment of coherence effects

Abstract

In this work, we investigate production of Drell-Yan (DY) pairs in proton-nucleus collisions in kinematic regions where the corresponding coherence length does not exceed the nuclear radius, RA, and the quantum coherence effects should be treated with a special care. The results for the nucleusto-nucleon production ratio available in the literature so far are usually based on the assumption of a very long coherence length (LCL) lc ≫ RA. Since the onset of coherence effects is controlled by the coherence length lc, we estimated its magnitude in various kinematic regions of the DY process and found that the LCL approximation should not be used at small and medium c.m. collision energies ( √ s 200 GeV) as well as at large dilepton invariant masses. In order to obtain realistic predictions, we computed for the first time the DY cross section using the generalised color dipole approach based on the rigorous Green function formalism, which naturally incorporates the color transparency and quantum coherence effects and hence allows to estimate the nuclear shadowing with no restrictions on the CL. In addition to the shadowing effect, we studied a complementary effect of initial state interactions (ISI) that causes an additional suppression at large values of the Feynman variable. Numerical results for the nuclear modification factor accounting for the ISI effect and the finite lc are compared to the data available from the fixed-target FNAL measurements and a good agreement has been found. Besides, we present new predictions for the nuclear suppression as a function of dilepton rapidity and invariant mass in the kinematic regions that can be probed by the RHIC collider as well as by the planned AFTER@LHC and LHCb fixed-target experiments. I. INTRODUCTIONHadronic production of massive lepton pairs, known as the Drell-Yan (DY) process, is a clean, precise and controllable probe for short-distance dynamics and partonic structure of hadrons (for a recent review see, e.g. Ref.[1]). In particular, the DY process on nuclear targets is an ideal tool to probe and to quantify the initial state interaction (ISI), saturation, gluon shadowing and coherence effects in a clean environment due to the absence of final-state interactions and fragmentation processes typically associated with energy loss or absorption phenomena [2]. The corresponding predictions for the nucleus-to-nucleon ratio known as the nuclear modification factor R pA have been obtained using the color dipole approach [3][4][5][6][7][8][9][10][11][12][13] which is known to provide as precise predictions for the DY cross section in pp collisions as the Next-to-Leading-Order (NLO) collinear factorisation framework. In the color dipole picture, the DY process off nuclei looks as γ * Bremsstrahlung off a projectile quark propagating through the nuclear medium [6]. Remarkably, the dipole framework enables us to include the coherence effects in nuclear collisions naturally from the first principles by means of the generalised path-integral (or Green function) formulation (se...

Mapping the dominant regions of the phase space associated with cc¯ production relevant for the prompt atmospheric neutrino flux

“…Recently, the Drell-Yan process in the dipole picture and the associated kinematic constraints has been thoroughly discussed by some of us in Refs. [49,50,59] while the higher-twist corrections remain uncertain. A proper analysis of this issue for heavy flavor production in the dipole picture is left for a future work.…”

“…Recently, the Drell-Yan process in the dipole picture and the associated kinematic constraints has been thoroughly discussed by some of us in Refs. [49,50,59] while the higher-twist corrections remain uncertain.…”

Diffractive dijet production: Breakdown of factorization

“…The light-cone dipole approach enables to incorporate such effects coherently at the amplitude level, which has been previously proven to work well in the diffractive Abelian radiation processes [10][11][12] and diffractive heavy flavor production [13]. In this paper, following the original studies of inclusive [25,26] and diffractive diffractive gluon radiation [13,24,48], we apply the light-cone dipole approach to the analysis of inclusive and diffractive gluon radiation beyond QCD factorisation. By comparing the dipole model results with the Tevatron data for the SD-to-inclusive ratio, we check whether the gap survival effects are properly accounted for in the dipole treatment of the diffractive non-Abelian radiation.…”

Nuclear shadowing in DIS at electron-ion colliders

“…One of the main topic, which is proposed to be studied by the future experiments at electron-ion colliders (EICs) [1][2][3][4] using present RHIC and LHC facilities, represents the nuclear shadowing at small values of Bjorken x Bj . This gives the main motivation for study of possible sources causing a suppression not only in deep-inelastic scattering (DIS) off nuclei (see [5,6], for example), but also in other exclusive processes at large energies, like diffractive photo-and electroproduction of vector mesons on nuclei (see [7][8][9][10][11], for example), the Drell-Yan process (see [12][13][14], for example), as well as the inclusive hadron production in proton-nucleus collisions (see [15][16][17], for example).…”