Rapidity and transverse-momentum dependence of the inclusive J/ψ nuclear modification factor in p-Pb collisions at s N N $$ \sqrt{s_{N\ N}} $$ = 5.02 TeV

Abstract

Abstract:We have studied the transverse-momentum (p T ) dependence of the inclusive J/ψ production in p-Pb collisions at √ s NN = 5.02 TeV, in three center-of-mass rapidity (y cms ) regions, down to zero p T . Results in the forward and backward rapidity ranges (2.03 < y cms < 3.53 and −4.46 < y cms < −2.96) are obtained by studying the J/ψ decay to µ + µ − , while the mid-rapidity region (−1.37 < y cms < 0.43) is investigated by measuring the e + e − decay channel. The p T dependence of the J/ψ production cross section and nuclear modification factor are presented for each of the rapidity intervals, as well as the J/ψ mean p T values. Forward and mid-rapidity results show a suppression of the J/ψ yield, with respect to pp collisions, which decreases with increasing p T . At backward rapidity no significant J/ψ suppression is observed. Theoretical models including a combination of cold nuclear matter effects such as shadowing and partonic energy loss, are in fair agreement with the data, except at forward rapidity and low transverse momentum. The implications of the p-Pb results for the evaluation of cold nuclear matter effects on J/ψ production in Pb-Pb collisions are also discussed. JHEP06(2015)055The suppression of charmonia, bound states of c andc quarks, and in particular of the J/ψ state, has long been proposed as a signature for the formation of a plasma of quarks and gluons (QGP) [1] in ultrarelativistic nucleus-nucleus collisions. However, it was soon realized that charmonium production can also be modified by nuclear effects not necessarily related to QGP formation [2]. These so-called cold nuclear matter (CNM) effects can be investigated by studying charmonium production in proton-nucleus (p-A) collisions as confirmed by the analysis of results obtained by several fixed-target (SPS [3, 4], HERA [5] and Tevatron [6]) and collider (RHIC [7] and LHC [8, 9]) experiments.Theoretical models have studied the production of charmonium in p-A collisions and the effects of the surrounding cold nuclear medium by introducing various mechanisms which include nuclear shadowing, gluon saturation, energy loss and nuclear absorption. Models [10][11][12] inspired by Quantum ChromoDynamics (QCD) describe charmonium production as a two-step process, with the cc pair created in a hard parton scattering, followed by its evolution into a bound state with specific quantum numbers. The pair creation is sensitive to the Parton Distribution Functions (PDFs) in both colliding partners and, at high energy, occurs mainly via gluon fusion. Although PDFs are known to be modified in a nuclear environment, information on the dependence of such modifications on the fraction x (Bjorken-x) of the nucleon momentum carried by the gluons and on the four-momentum squared Q 2 transferred in the scattering is still limited [13][14][15]. Charmonium production measurements can therefore provide insight into the so-called nuclear shadowing, i.e., on how the nucleon gluon PDFs are modified in a nucleus.Modifications of the initial state of the ...

Towards an automated tool to evaluate the impact of the nuclear modification of the gluon density on quarkonium, D and B meson production in proton–nucleus collisions

“…The very same fits are however consistent with the ATLAS data in the same P T regime, which possibly indicates an underestimation of the systematical experimental uncertainties in that regime. [66], ALICE [67] and ATLAS [68] our results and the measurements of LHCb [66], ALICE [69] and ATLAS [68] 4 Results 4.1 Rapidity and transverse-momentum dependence of the production cross-section in pPb collisions at √ s N N = 5.02 TeV Now that we have described our approach, we can present our results for the cross-section for quarkonium and D 0 production in proton-lead ( pPb) collisions at the LHC. In the following, we show comparisons with all the existing data.…”

“…The transverse-momentum P T spectra (dσ pPb /d P T ) of promptly produced J/ψ in pPb collisions at [67] and ATLAS data [68] are given in Fig. 2c, d respectively.…”

Prospects for Quarkonium Measurements in p–A and A–A Collisions at the LHC

“…This model could also reproduce the main features of the available data for J/ψ [34,32,35] and ϒ (1S) [36,37] production at low p T , where the strongest modifications are observed both in data as well as in the model. In summary, a variety of models exists and there is at the moment no conclusive and broadly accepted interpretation of the available data.…”

“…The use of nuclear parton distribution functions (nPDF's) even available at NLO [28,29,30,31], in practice most calculations employ the EPS09 parameterisations [29], can at least approximately account for the measured J/ψ [32,33,34,35] and the ϒ (1S) [36,37] nuclear modification factors. Nevertheless, the currently available gluon distributions in the relevant region of Bjorken-x suffer from large uncertainties already for the nucleon but even more for the nucleus in absence of lepton-ion collider data or other sensitive inputs.…”

“…Extrapolations to the expected nondeconfined nuclear modifications in A-A collisions based on p-A data can only be done under assumptions correct within certain frameworks. Nevertheless, first data driven attempts were pursued [35], which prove the power of the precise measurements in p-A collisions to constrain the expectations in A-A collisions if the underlying assumptions are valid.…”