Probing shadowed nuclear sea with massive gauge bosons in the future heavy-ion collisions

Abstract

The production of the massive bosons Z 0 and W ± could provide an excellent tool to study cold nuclear matter effects and the modifications of nuclear parton distribution functions (nPDFs) relative to the parton distribution functions (PDFs) of a free proton in high-energy nuclear reactions at the LHC as well as in heavy-ion collisions (HIC) with much higher center-of-mass energies available in the future colliders. In this paper we calculate the rapidity and transverse momentum distributions of the vector boson and their nuclear modification factors in p + Pb collisions at √ s N N = 63 TeV and in Pb + Pb collisions at √ s N N = 39 TeV in the framework of perturbative QCD by utilizing three parametrization sets of nPDFs: EPS09, DSSZ, and nCTEQ. It is found that in heavy-ion collisions at such high colliding energies, both the rapidity distribution and the transverse momentum spectrum of vector bosons are considerably suppressed in wide kinematic regions with respect to p + p reactions due to large nuclear shadowing effect. We demonstrate that the massive vector boson production processes with sea quarks in the initial state may give more contributions than those with valence quarks in the initial state; therefore in future heavy-ion collisions the isospin effect is less pronounced and the charge asymmetry of the W boson will be reduced significantly as compared to that at the LHC. A large difference between results with nCTEQ and results with EPS09 and DSSZ is observed in nuclear modifications of both rapidity and p T distributions of Z 0 and W in the future HIC.

Study ofW±andZboson production in proton-lead collisions at the LHC with Kulagin-Petti nuclear parton distributions

“…The NLO and next-to-next-to-leading (NNLO) coefficients for the partonic cross sections of the DY process and the hadronic W and Z boson production are well known [34][35][36][37][38][39]. It should be noted that the NNLO corrections to the boson-rapidity distributions in relativistic heavy-ion collisions are small at the LHC kinematics [18,19].…”

“…A good agreement between the NLO predictions and the CMS data [40] on Z 0 production is observed by using both the ABMP15 and the CT10 PDFs. Similarly, the DYNNLO program provides a good description of the W -boson production at the LHC [18,19]. as a function of the Z 0 rapidity.…”

“…The recent precision data from the CMS [9,10] and ATLAS [11,12] experiments offer the possibility to extend the study of W ± and Z 0 boson production to proton-lead collisions with √ s = 5.02 TeV per two colliding nucleons at the LHC [13][14][15][16][17][18][19][20][21]. Since the QCD factorization theorem [22] is expected to hold for nuclei, we can still describe this process in terms of pQCD, with the corresponding nuclear PDFs for the lead nucleus.…”

Predictions for p +Pb Collisions atsNN=5 TeV: Comparison With Data

“…Also note that forward Z 0 production proceeds via nuclear sea quarks, u s u s and d s d s (with only small higher order contributions from gluons), while backward Z 0 production is dominated by nuclear valence quarks, u v and d v . 147 Therefore the forward-backward ratio can schematically be written as…”

“…The nuclear effect in the forward region is thus predominantly related to sea quark shadowing while that in the backward direction is mainly due to EMC effects on the valence quarks. 142,147 Because the forward and backward yields in the rapidity region covered by LHCb are rather small, 146 the experimental precision should be improved for more robust comparisons of the calculations to data. Unfortunately, the rapidity regions of CMS and LHCb do not overlap.…”