<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>J</mml:mi><mml:mo>/</mml:mo><mml:mi>ψ</mml:mi></mml:mrow></mml:math>suppression at forward rapidity in Au<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:math>Au collisions at<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msqrt><mml:msub><mml:mi>s</mml:mi><mml:mrow><mml:mi>N</mml:mi><mml:mi>N</mml:mi></mml

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We present a measurement of inclusive J/ψ production in p-Pb collisions at √ s NN = 5.02 TeV as a function of the centrality of the collision, as estimated from the energy deposited in the Zero Degree Calorimeters. The measurement is performed with the ALICE detector down to zero transverse momentum, p T , in the backward (−4.46 < y cms < −2.96) and forward (2.03 < y cms < 3.53) rapidity intervals in the dimuon decay channel and in the mid-rapidity region (−1.37 < y cms < 0.43) in the dielectron decay channel. The backward and forward rapidity intervals correspond to the Pb-going and p-going direction, respectively. The p T -differential J/ψ production cross section at backward and forward rapidity is measured for several centrality classes, together with the corresponding average p T and p T 2 values. The nuclear modification factor is presented as a function of centrality for the three rapidity intervals, and as a function of p T for several centrality classes at backward and forward rapidity. At mid-and forward rapidity, the J/ψ yield is suppressed up to 40% compared to that in pp interactions scaled by the number of binary collisions. The degree of suppression increases towards central p-Pb collisions at forward rapidity, and with decreasing p T of the J/ψ. At backward rapidity, the nuclear modification factor is compatible with unity within the total uncertainties, with an increasing trend from peripheral to central p-Pb collisions. The ALICE collaboration 26 IntroductionCharmonia, bound states of charm and anti-charm quark pairs, are extensively used to study the interplay between the perturbative and the non-perturbative regimes of Quantum ChromoDynamics (QCD) [1]. Charmonium production mechanism can be understood as a hard scattering, describing the charm anti-charm quark pair production, followed by the evolution of the pair into a bound state via a non-perturbative process. Models such as colour evaporation (CEM) [2, 3], colour singlet (CSM) [4] and non-relativistic QCD (NRQCD) [5] are used to describe the charmonium production in hadronic collisions. None of these models has so far provided a consistent description of the production cross section and polarisation measured in proton-proton (pp) collisions [1,6]. The 1S vector state, the J/ψ meson, is abundantly produced in hadronic collisions at high energy and measurable through its leptonic decays. Its inclusive production contains contributions from direct J/ψ, from decays of higher-mass excited states, ψ(2S) and χ c , as well as from non-prompt J/ψ, from weak decays of beauty hadrons. In proton-nucleus (p-A) collisions, several effects related to the nuclear medium and commonly denoted as cold nuclear matter effects (CNM) can affect the production of charmonia. The Parton Distribution Functions (PDFs) of nucleons bound in nuclei are modified compared to those of free nucleons [7][8][9]. These functions depend, in particular, on the fraction of the nucleon momentum, Bjorken-x (x Bj ), carried by the probed parton. In the collision energy...

Section: Jhep11(2015)127mentioning

confidence: 99%

Centrality dependence of inclusive J/ψ production in p-Pb collisions at s N N = 5.02 $$ \sqrt{s_{\mathrm{NN}}}=5.02 $$ TeV

Adam¹,

Adamová²,

Aggarwal³

et al. 2015

Self Cite

“…It was predicted that the J/ψ formation is suppressed in a QGP due to the screening of the cc potential in the presence of free colour charges [5]. Experimentally, a suppression of the inclusive J/ψ yield in heavy-ion collisions relative to the corresponding yield in pp, scaled by the number of binary nucleon-nucleon collisions, has been observed at the Super Proton Synchrotron (SPS) [6][7][8] and the Relativistic Heavy Ion Collider (RHIC) [9,10]. The level of suppression was found to be similar at SPS and RHIC, despite the significantly different collision energy.…”

Section: Introductionmentioning

confidence: 99%

Inclusive, prompt and non-prompt J/ψ production at mid-rapidity in Pb-Pb collisions at s N N = 2.76 $$ \sqrt{s_{\mathrm{NN}}}=2.76 $$ TeV

Adam

Adamová

Aggarwal

et al. 2015

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Abstract:The transverse momentum (p T ) dependence of the nuclear modification factor R AA and the centrality dependence of the average transverse momentum p T for inclusive J/ψ have been measured with ALICE for Pb-Pb collisions at √ s NN = 2.76 TeV in the e + e − decay channel at mid-rapidity (|y| < 0.8). The p T is significantly smaller than the one observed for pp collisions at the same centre-of-mass energy. Consistently, an increase of R AA is observed towards low p T . These observations might be indicative of a sizable contribution of charm quark coalescence to the J/ψ production. Additionally, the fraction of non-prompt J/ψ from beauty hadron decays, f B , has been determined in the region 1.5 < p T < 10 GeV/c in three centrality intervals. No significant centrality dependence of f B is observed. Finally, the R AA of non-prompt J/ψ is discussed and compared with model predictions. The nuclear modification in the region 4.5 < p T < 10 GeV/c is found to be stronger than predicted by most models. The ALICE collaboration 26 IntroductionHeavy-ion collisions at high energies allow the study of strongly interacting matter under extreme conditions. Calculations based on Quantum-Chromo-Dynamics (QCD) on the lattice indicate that the hot and dense medium created in these collisions behaves like a strongly coupled Quark-Gluon Plasma (QGP) [1][2][3][4]. Heavy quarks are an important probe for the properties of this state of matter, since they are produced via hard partonic collisions at a very early stage and thus experience the complete evolution of the system. Quarkonium states, i.e. bound states of a heavy quark and anti-quark such as the J/ψ meson (cc state) are of particular interest. It was predicted that the J/ψ formation is suppressed in a QGP due to the screening of the cc potential in the presence of free colour charges [5]. Experimentally, a suppression of the inclusive J/ψ yield in heavy-ion collisions relative to the corresponding yield in pp, scaled by the number of binary nucleon-nucleon collisions, has been observed at the Super Proton Synchrotron (SPS) [6][7][8] and the Relativistic Heavy Ion Collider (RHIC) [9,10]. The level of suppression was found to be similar at SPS and RHIC, despite the significantly different collision energy. More recently, the nuclear modification of J/ψ was also measured for Pb-Pb collisions at the LHC [11][12][13]. While at high transverse momentum (p T > 4 GeV/c) the suppression factor is at the same level as the one observed at RHIC in the low p T region, a significant reduction of the suppression is measured towards lower p T . This has been interpreted as the effect of an additional contribution to J/ψ production at low p T , due to the combination of correlated or uncorrelated c and c quarks [14,15]. This contribution becomes sizable at LHC energies, since the number of cc pairs is much higher than at lower energies. Assuming that a deconfined phase is produced and that all the J/ψ are dissociated, this process happens at the chemical freezeout stage of the fireball ...

“…In heavy-ion collisions, a superposition of hot and cold nuclear matter effects is expected, and a quantitative evaluation of the latter is an important prerequisite for a detailed understanding of the former. At lower energy, both at SPS [22][23][24] and RHIC [25,26], a suppression of J/ψ production, in addition to the CNM effects estimated from p-A(d-A) collisions, was indeed observed.A suppression of J/ψ production has been measured in Pb-Pb collisions at the LHC [27-31]. It was quantified via the nuclear modification factor, i.e., the ratio of the Pb-Pb yields with respect to those measured in pp at the same energy, scaled by the number of binary nucleon-nucleon collisions.…”

mentioning

confidence: 99%

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

Adam¹,

Adamová²,

Aggarwal³

et al. 2015

Self Cite

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 ...