Nuclear modification of forward Drell-Yan production at the LHC

Abstract

Forward Drell-Yan production at high energy can provide important constraints on gluon densities at small x, in the saturation regime. In this work, we focus on the nuclear modification of this process, which could be measured at the LHC in the near future. For this, we employ the color dipole approach, using the optical Glauber model to relate the dipole cross section of a nucleus to the one of a proton. Combining these results with our earlier results for forward J=ψ production, we compute the ratio of the nuclear modification factors of these two processes. This observable was recently suggested as a way to distinguish between initial and final state effects in forward particle production.

Isolated photon production in proton-nucleus collisions at forward rapidity

“…[22] and extended to nuclei using an optical Glauber procedure relying on standard nuclear geometry. The same dipole cross sections, without any additional parameters, have previously been used to calculate single inclusive particle production [22], forward J=Ψ production [23,24] and DrellYan cross sections [32] in proton-proton and proton-nucleus collisions. The range of processes addressed in these works demonstrates the universality and predictive power of the dilute-dense CGC framework, combining the dipole picture of DIS with the "hybrid" formalism for forward hadronic collisions.…”

Prospects for quarkonium studies at the high-luminosity LHC

“…However, it should be noted that a full cancellation of the scale uncertainties is assumed in these different processes, which may not be justified and needs to be investigated with further studies. A calculation of this ratio in the CGC formalism shows that it is relatively flat and close to unity [691]. Therefore this observable could potentially help discriminate between models based on the energy loss and on nuclear modifications of parton densities -with or without saturation.…”

“…While absolute cross sections for this process are affected by rather large fragmentation functions uncertainties [689], the NMF is a more robust observable and the comparison with other processes could help to discriminate between different nuclear suppression mechanisms. For instance, in the CGC approach, the suppression at forward rapidities is similar for light hadrons and Drell-Yan production [690,691]. On the other hand, in the coherent energy loss model, the first process shows a sizeable suppression [692,693] while the NMF for Drell-Yan is unity at forward rapidity since one considers the production of a colourless object [694].…”

Forward rapidity isolated photon production in proton-nucleus collisions

“…3. Nuclear modifiction factor for D-mesons [7] (left) and double ratio of nuclear modification factor for J/ψ divided by the one for Drell-Yan-dileptons [8] (right). Note that the LHCb data in this plot is preliminary and the normalization in the finalized data [9] is somewhat lower.…”