Global analysis of J/psi suppression in cold nuclear matter
Vi-Nham Tram, Francois Arleo
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6 pages, 3 figures To appear in the proceedings of 3rd International Conference On Hard And Electromagnetic Probes Of High-Energy Nuclear Collisions (HP2008) Eur.Phys.J.C
Interpreting the J/psi suppression reported in nucleus--nucleus collisions at SPS and RHIC requires the quantitative understanding of cold nuclear matter effects, such as the inelastic rescattering of J/psi states in nuclei or the nuclear modification of parton densities. With respect to our former Glauber analysis, we include in the present work the new PHENIX d--Au measurements, and analyze as well all existing data using the EPS08 nuclear parton densities recently released. The largest suppression reported in the new PHENIX analysis leads in turn to an increase of sigma from 3.5 +/- 0.3 mb to 5.4 +/- 2.5 mb using proton PDF. The stronger x-dependence of the G^{A}/G^p ratio in EPS08 as compared to e.g. EKS98 shifts the cross section towards larger values at fixed target energies (x_2 ~ 0.1) while decreasing somehow the value extracted at RHIC (x_2 ~10^{-2}).
Two decades ago Matsui and Satz suggested that Debye screening in the quark-gluon plasma would result in J/psi suppression in heavy ion collisions. Much has happened in the subsequent years, and the picture of quark-gluon plasma at present is rapidly evolving - what does it imply for the J/psi suppression? What are the recent RHIC and SPS results trying to tell us? What else has to be done? This talk is an attempt to address these questions.
The anomalous J/psi suppression in Pb-Pb collisions at 158A GeV observed recently by NA50 can be explained as due to the transition to a new phase of strong J/psi absorption, which sets in when the local energy density exceeds about 3.4 GeV/fm**3.
A parameter-free calculation for J/Psi suppression in pA collisions, based on the dipole description, is confronted with the new data from the PHENIX experiment. Achieving good agreement, we employed this model predicting the contribution of initial state interactions (ISI) to J/Psi suppression in AA collisions. Such a transition from pA to AA is not straightforward, since involves specific effects of double color filtering and boosting of the saturation scale. Relying on this refined ISI contribution, we updated the previous analysis of RHIC data on J/Psi production in Cu-Cu and Au-Au collisi…
The momentum diffusion effect of the quark pair due to the multiple scattering in a nuclear medium is studied to explain the observed J/psi yields in SPS experiments. The resulting suppression is found to be insufficient to reproduce the J/psi yield in Pb-Pb collisions at SPS energy.
Based on a Glauber model, a statistical analysis of all mid-rapidity J/psi hadroproduction and leptoproduction data on nuclear targets is carried out. This allows us to determine the J/psi-nucleon inelastic cross section, whose knowledge is crucial to interpret the J/psi suppression observed in heavy-ion collisions, at SPS and at RHIC. The values of sigma are extracted from each experiment. A clear tension between the different data sets is reported. The global fit of all data gives sigma=3.4+/-0.2 mb, which is significantly smaller than previous estimates. A similar value, sigma=3.5+/-0.2 mb,…
The observed J/psi suppression in Pb+Pb collisions shows a drop at those large values of the transverse energy E_T which arise from fluctuations. The validity of existing models for J/psi suppression can be extended into this domain of E_T by introducing an ad hoc factor proportional to E_T. We propose a formalism in which the influence of E_T fluctuations on the J/psi suppression can be calculated and discuss the conditions under which the ad hoc factor is obtained.
The recent data for E866 experiment on the x_F dependence for charmonium suppression in pA collisions at 800 GeV are analyzed using a time- and energy-dependent preformed charmonium absorption cross section σ_{abs}^ψ(τ,\sqrt{s}). For \sqrt{s}=10 GeV the initially (τ=0) produced premeson has an absorption cross section of σ_{pr}~3mb. At the same energy but for τ-> \infty one deduces for the total cross sections σ_{tot}^{J/Psi N}=(2.8\pm 0.3)mb, σ_{tot}^{J/Psi N}= (10.5\pm 3.6)mb. The date are compatible with a formation time τ_{1/2}=0.6 fm/c.
The effects of energy loss in cold nuclear matter on J/psi suppression in p-A collisions are studied. A simple model based on first principles and depending on a single free parameter is able to reproduce J/psi suppression data at large xF and at various center-of-mass energies. These results strongly support energy loss as a dominant effect in quarkonium suppression. They also give some hint on its hadroproduction mechanism suggesting color neutralization to happen on long time-scales. Predictions for J/psi and Upsilon suppression in p-Pb collisions at the LHC are made.
We study the characteristic features of J/Psi suppression by deconfinement. A first order phase transition leads to an essentially discontinuous onset of anomalous J/Psi suppression. The different energy densities required for the dissociation of different charmonium states result in a two-step suppression pattern, in which first the J/Psi's from chi decays are suppressed and subsequently the directly produced J/Psi states. Combining both features leads to a unique form of J/Psi suppression in a deconfining medium.
The strong "anomalous" J/Psi suppression observed recently by the NA50 Collaboration at CERN SPS has attracted considerable attention. Is it the first signature of a long-awaited quark-gluon plasma, or just a peculiar combination of "conventional" effects acting together to produce the puzzling pattern observed experimentally? This talk is an attempt to summarize the theoretical explanations proposed during the last two years.
The effects of parton energy loss and pT-broadening in cold nuclear matter on the pT and centrality dependence, at various rapidities, of J/psi suppression in p-A collisions are investigated. Calculations are systematically compared to E866 and PHENIX measurements. The very good agreement between the data and the theoretical expectations further supports pT-broadening and the associated medium-induced parton energy loss as dominant effects in J/psi suppression in high-energy p-A collisions. Predictions for J/psi (and Upsilon) suppression in p-Pb collisions at the LHC are given.
1. Introduction 2. Charmomium Dissociation and Colour Deconfinement 3. J/Psi Production in Nuclear Collisions 4. Anomalous J/Psi Suppression 5. Outlook and Summary
We investigate the in-medium modification of the charmonium break-up processes due to the Mott effect for light (pi) and open-charm (D, D*) mesons at the chiral/deconfinement phase transition. A model calculation for the process J/Psi + pi -> D + \bar D* + h.c. is presented which demonstrates that the Mott effect for the D-mesons leads to a threshold effect in the thermal averaged break-up cross section. This effect is suggested as an explanation of the phenomenon of anomalous J/Psi suppression in the CERN NA50 experiment.
We present new results based on an improved version of the Glauber model, used to describe the nuclear absorption of J/psi in reactions between nuclei at high energy. The excitation of the colour degrees of freedom of nucleons, due to collisions mediated by one-gluon exchange, is taken into account. It is found that the proposed mechanism leads to larger nuclear absorption of J/psi than previously considered.
We estimate the survival probability of $J/ψ$ in relativistic heavy-ion collisions, using both short-distance QCD and nuclear absorption mechanism. The suppression is found to be almost 100 percent for a thermally equilibrating quark-gluon plasma. The measurement of such a huge suppression of $J/ψ$ may suggest the existence of a deconfined partonic medium, possibly a thermalised quark-gluon plasma, at RHIC.
Prediction for transverse energy dependence of $J/ψ$ to Drell-Yan ratio in Au+Au collisions at RHIC energy was obtained in a model which assume 100% absorption of $J/ψ$ above a threshold density. The threshold density was obtained by fitting the NA50 data on $J/ψ$ suppression in Pb+Pb collisions at SPS energy. At RHIC energy, hard processes may be important. Prediction of $J/ψ$ suppression with and without hard processes were obtained. With hard processes included, $J/ψ$'s are strongly suppressed.
Using a coherence time extracted from high precision proton-nucleus Drell-Yan measurements and a nuclear absorption cross section extracted from pA charmonium production experiments, we study J/psi production and absorption in nucleus-nucleus collisions. We find that coherence time effects are large enough to affect the measured J/psi-to-Drell-Yan ratio. The S+U data at 200A GeV/c measured by NA38 are reproduced quantitatively without the introduction of any new parameters. However, when compared with recent NA50 measurements for Pb+Pb at 158A GeV/c, the data is not reproduced in trend or in m…
The nonlinear effect of gluon depletion in the collision of large nuclei can be large. It is due to multiple scatterings among comoving partons initiated by primary scattering of partons in the colliding nuclei. The effect can give rise to substantial suppression of $J/ψ$ production in very large nuclei, even if the linear depletion effect is insignificant for the collisions of nuclei of smaller sizes. This mechanism offers a natural explanation of the enhanced suppression in the Pb-Pb data recently observed by NA50.
We investigate the in-medium modification of the charmonium breakup processes due to the Mott-effect for D-mesons at the chiral phase transition. A model calculation for the process J/Psi+pi --> D+D^*+ h.c. is presented which demonstrates that threshold effects in the thermal averaged breakup cross section can be explained as a Mott transition where final state quark-antiquark bound states enter the continuum of resonant states at the QCD phase transition. Applications to heavy-ion collisions within a modified Glauber model scenario and the phenomenon of anomalous J/$ψ$ suppression in the CERN…
The geometric clustering of partons in the transverse plane of nuclear collisions leads for increasing A or sqrt(s) to percolation. In the resulting condensate, the partons are deconfined but not yet in thermal equilibrium. We discuss quarkonium dissociation in this precursor of the quark-gluon plasma, with an onset of dissociation when the saturation scale of the parton condensate reaches that of the given quarkonium state.
We discuss the J/psi suppression in the framework of multiple collision models. From the analysis of the Pb-Pb NA50 data we conclude that the strength of the absorption has increased, but we find no clear evidence for the formation of the quark-gluon plasma.
Hadrons produced in high-energy heavy-ion collisions can suppress the production of J/psi and other charmonium states by charmonium spontaneous dissociation as the hot hadronic environment alters the interaction between the charm quark and charm antiquark. Furthermore, hadrons can thermalize a charmonium to excite it to higher charmonium states which subsequently dissociate spontaneously. They can also collide with a charmonium to lead to its prompt dissociation into an open charm pair.
A systematic analysis of the L-dependence of the J/psi-suppression in the data of the CERN NA38 and NA50 experiments shows that the anomalous suppression in the 1995 Pb-Pb data is at best a 4$σ$ effect at any of the L-values for the Pb-Pb data, where L is the geometrical mean path length of the J/psi in the colliding nuclei. Possible implications for the 1996 data are discussed.
We consider an ideal gas of massive hadrons in thermal and chemical equilibrium. The finite-size gas expands longitudinally in accordance with Bjorken law. Also the transverse expansion in a form of the rarefaction wave is considered. We show that J/Psi suppression in such an environment, when combined with the disintegration in nuclear matter, agrees qualitatively well with NA38 and NA50 data.
We study the clustering of colour strings in the transverse plane of nucleus-nucleus collisions and argue that deconfinement sets in when the string density within a cluster reaches a critical value. We show that this implies a minimal cluster size at the onset of deconfinement, which in turn results in discontinuous behaviour for J/Psi suppression.
The depletion of gluons as the parton flux traverses a nucleus in a heavy-ion collision can influence the production rate of heavy-quark states. Thus the suppression of $J/ψ$ can be due to gluon depletion in the initial state in addition to nuclear and hadronic absorption in the final state. A formalism is developed to describe the depletion effect. It is shown that, without constraints from other experimental facts beside the $J/ψ$ suppression data in $pA$ and $AB$ collisions, it is not possible to determine the relative importance of depletion vs absorption. Possible relevance to the enhance…
Parton percolation provides geometric deconfinement in the pre-equilibrium stage of nuclear collisions. The resulting parton condensate can lead to charmonium suppression. We formulate a local percolation condition viable for non-uniform collision environments and show that it correctly reproduces the suppression observed for S-U and Pb-Pb collisions at the SPS. Using this formulation, we then determine the behavior of J/Psi suppression for In-In collisions at the SPS and for Au-Au collisions at RHIC.
We review the search for the quark-gluon plasma using the signal of the suppression of J/psi production in high-energy heavy-ion collisions. Recent observations of anomalous J/psi suppression in high-energy Pb-Pb collisions observed by the NA50 Collaboration are examined and compared with earlier results from pA and nucleus-nucleus collisions with heavy ions of smaller mass numbers. The anomalous suppression of J/psi production in Pb-Pb collisions can be explained as due to the occurrence of a new phase of strong J/psi absorption, which sets in when the number of nucleon-nucleon collisions at …
We re-analyse the data on J/psi cross sections for proton-nucleus and nucleus-nucleus collisions obtained by the CERN experiments NA38, NA51 and NA50. Our systematic analysis of error propagation shows that the no anomalous suppression of J/psi in Pb-Pb collisions can be substantiated at 95% confidence limit. The significance of the NA50 result would be enhanced by more precise p-A data on J/psi cross sections.
The experimental ratio of $ψ'$ to $J/ψ$ is approximately a constant in $pA$ collisions, but decreases as the transverse energy increases in nucleus-nucleus collisions. These peculiar features can be explained as arising from approximately the same $c \bar c$-baryon absorption cross section for $ψ'$ and $J/ψ$ but greater disruption probabilities for $ψ'$ than for $J/ψ$ due to the interaction of the $c\bar c$ system with soft particles produced in baryon-baryon collisions.
The azimuthal asymmetry of $J/ψ$ suppression in non-central heavy-ion collisions is studied within a dynamic model of $J/ψ$ suppression in a deconfined partonic medium. Within this model, $J/ψ$ suppression in heavy-ion collisions is caused mainly by the initial state nuclear absorption and dissociation via gluon-$J/ψ$ scattering in deconfined partonic medium. Only the second mechanism gives arise to azimuthal asymmetry of the final $J/ψ$ production. We demonstrate that if there is an onset of suppression by quark-gluon plasma (QGP) in the NA50 data, it must be accompanied by the non-vanishing …
We study J/psi suppression in AB collisions assuming that the charmonium states evolve from small, color transparent configurations. Their interaction with nucleons and nonequilibrated, secondary hadrons is simulated using the microscopic model UrQMD. The Drell-Yan lepton pair yield and the J/psi/Drell-Yan ratio are calculated as a function of the neutral transverse energy in Pb+Pb collisions at 160 GeV and found to be in reasonable agreement with existing data.
When the cross section of J/psi production is considered varying with the energy of the nucleon-nucleon interaction the production of J/psi in pA and AA collisions has been studied using FRITIOF Model. The calculation shows that the cross section of J/psi production "per nucleon-nucleon collision" decreases with increasing mass number and centrality as a consequence of continuous energy loss of the projectile nucleons to the target nucleons in their successive binary nucleon-nucleon collisions . We have compared our model predictions with the experimental data of J/psi production.
We point out that dissociation of J/Psi by partons (mostly gluons) present in the intermediate stage of heavy-ion collisions can explain J/Psi suppression observed recently by the NA-50 Collaboration at the CERN-SPS in Pb-Pb interactions. Suppression by intermediate stage gluons represents an additional multiplicative factor to that given by Gerschel-Hufner mechanism. The agreement with data on J/Psi suppression both in light- ions induced nuclear collisions and in Pb-Pb interactions requires that the life-time of intermediate gluons increases with nucleon numbers of colliding nuclei. In our m…
We consider the production of the J/psi mesons in heavy ion collisions at RHIC energies in the statistical coalescence model with an exact (canonical ensemble) charm conservation. The c\bar{c} quark pairs are assumed to be created in the primary hard parton collisions, but the formation of the open and hidden charm particles takes place at the hadronization stage and follows the prescription of statistical mechanics. The dependence of the J/psi production on both the number of nucleon participants and the collision energy is studied. The model predicts the J/psi suppression for low energies, w…
Short-distance QCD is employed to calculate the $J/ψ$ survival probability in an equilibrating parton gas, whose evolution is governed by a set of master rate equations. Partons in the early stage of high-energy nuclear collisions may initially not be in equilibrium, but their average transverse momentum is sufficiently high to break up a $Q\bar{Q}$ bound state. Such a break-up during the evolution of the parton gas is shown to cause a substantial $J/ψ$ suppression at both RHIC and LHC energies, using realistic estimates of the initial parton densities. The transverse momentum dependence of th…
The NA50 Collaboration has recently observed a strong suppression of J/Psi production in Pb-Pb collisions at 158 Gev/n. We show that this recent observation finds a quantitative explanation in a model which relates the suppression mechanism to the local energy density, whose value is higher in Pb-Pb collisions than in any other system studied previously. The sensitivity of the phenomenon to small changes in the energy density could be suggestive of quark-gluon plasma formation.
We present baseline calculations of initial-state shadowing and final-state absorption effects on J/psi production in nucleus-nucleus collisions at the Relativistic Heavy Ion Collider. We show predictions for Au+Au and Cu+Cu collisions at \sqrt{S_{NN}}=200 GeV and Cu+Cu collisions at \sqrt{S_{NN}} = 62 GeV as a function of the rapidity, y, and the number of binary nucleon-nucleon collisions, N_{\rm coll}.
It is shown that the strangeness enhancement and the J/psi anomalous suppression patterns observed in heavy ion collisions at top SPS energy, sqrt(s)_NN = 17.2 GeV, exhibit an interesting correlation if studied as a function of the transverse size of the interaction region. The onset of both phenomena seems to occur when the size exceeds \approx 4 fm. Strangeness enhancement is defined in terms of the strangeness undersaturation factor gamma_S and J/psi anomalous suppression in terms of the deviation from the absorption expected in a purely hadronic scenario.
We discuss the interplay of screening, absorption and regeneration effects, on the quantum mechanical evolution of quarkonia states, within a time-dependent harmonic oscillator (THO) model with complex oscillator strength. We compare the results with data for R_AA/R_AA(CNM) from CERN and RHIC experiments. In the absence of a measurement of cold nuclear matter (CNM) effects at LHC we estimate their role and interpret the recent data from the ALICE experiment. We also discuss the temperature dependence of the real and imaginary parts of the oscillator frequency which stand for screening and abso…
Cold nuclear matter effects on J/psi production in proton-nucleus and nucleus-nucleus collisions are evaluated taking into account the specific J/psi production kinematics at the partonic level, the shadowing of the initial parton distributions and the absorption in the nuclear matter. We consider two different parton processes for the c-cbar pair production: one with collinear gluons and a recoiling gluon in the final state and the other with initial gluons carrying intrinsic transverse momentum. Our results are compared to RHIC observables. The smaller values of the nuclear modification fact…
We present a microscopic calculation of the breakup cross sections of $J/ψ$ and $ψ'$ on pions and nucleons as a function of the kinetic energy. These cross sections are used for the investigation of the $J/ψ$ to continuum and $ψ'/J/ψ$ ratios in ultrarelativistic heavy ion collisions. The contribution of produced comoving pions to the $ψ'/J/ψ$ signal is calculated. While this model can account for the data, the uncertainties in the parameter values do not allow to exclude the possibility of additional sources for charmonium absorption, like a resonance gas or the quark gluon plasma.
We define and compute from data the strong couplings of the X(3872) with both of the possible quantum numbers assignments J^{PC}=1^{++},2^{-+}. We use these to compute cross sections for J/psi resonance scattering into D Dbar*. As an application of the results obtained we revise the calculation of the J/psi absorption in a hot hadron gas to confront with recent RHIC observations in Au-Au collisions.
The observed features of $ψ'$ to $J/ψ$ suppression in $pA$ and nucleus-nucleus collisions can be explained in terms of a two-component absorption model. For the hard component of the absorption due to the interaction of the produced $c\bar c$ systems with baryons at high relative energies, the absorption cross sections are insensitive to the radii of the $c\bar c$ systems, as described by the Additive Quark Model. For the soft component due to the low energy $c \bar c$ interactions with soft particles produced by other baryon-baryon collisions, the absorption cross sections are greater for $ψ'…
Data from J/psi and psi' production in p-A collisions are used to determine the cross section for absorption of pre-resonance charmonium in nuclear matter. The J/psi suppression in O-Cu, O-U and S-U collisions is fully reproduced by the corresponding nuclear absorption, while Pb-Pb collisions show an additional suppression increasing with centrality. We study the onset of this change in terms of hadronic comover interactions and conclude that so far no conventional hadronic description can consistently account for all data. Deconfinement, starting at a critical point determined by central S-U …
We examine the production of J/$Ψ$ mesons in high energy hadron-nucleus collisions using models that account for both the initial state modification of parton distributions in nuclei and the final state interaction of the produced $c\bar c$ pairs. We show that, at the energies of current fixed target experiments, J/$Ψ$ production through quark-antiquark annihilation gives the largest contribution at $x_F > 0.5$, while gluon-gluon fusion dominates the production at smaller $x_F$. The observed J/$Ψ$ suppression at large $x_F$ is directly connected to nuclear shadowing in deeply inelastic scatter…
We show that, contrary to recent claims, the $J/ψ$ suppression resulting from its interaction with comovers does not saturate at large transverse energy $E_T$. On the contrary, it shows a characteristic structure - change of curvature near the knee of the $E_T$ distribution - which is due to the $E_T$ (or multiplicity) fluctuation, and agrees with recent experimental results.
The production of J/Psi's in nuclei is re-examined and the critical role of Feynman x distributions in the study of photoproduction and hadronic production of both J/Psi's and Drell-Yan dimuons is expatiated. The need to consider both initial and final state interactions and the key effect of initial state interactions on the total J/Psi cross section are demonstrated. We use a Woods-Saxon Monte Carlo simulation to obtain distributions of the numbers of collisions prior and subsequent to the charmonium production. With those results we relate the mean number of nucleon-nucleon collisions, $<n>…
We investigate the production of psi(2S) in nuclear collisions at RHIC and LHC energies. We first address charmonium production in 200 GeV d-Au collisions at RHIC; the strong suppression of psi' mesons observed in these reactions indicates mechanisms beyond initial cold nuclear matter effects. We find that a more complete treatment of hadronic dissociation reactions leads to appreciable psi' suppression in the hadronic medium of an expanding fireball background for d-Au collisions. When implementing the updated hadronic reaction rates into a fireball for 2.76 TeV Pb-Pb collisions at LHC, the r…
We consider the $J/Ψ$ suppression at a high energy heavy ion collision. An ideal gas of massive hadrons in thermal and chemical equilibrium is formed in the central region. The finite-size gas expands longitudinally in accordance with Bjorken law. The transverse expansion in a form of the rarefaction wave is taken into account. We show that $J/Ψ$ suppression in such an environment, when combined with the disintegration in nuclear matter, gives correct evaluation of NA38 and NA50 data in a broad range of initial energy densities.
Prompt gluons are an additional source for charmonium suppression in nuclear collisions, in particular for nucleus-nucleus collisions. These gluons are radiated as bremsstrahlung in N-N collisions and interact inelastically with the charmonium states while the nuclei still overlap. The spectra and mean number <n_g> of the prompt gluons are calculated perturbatively and the gluon-Psi inelastic cross section is estimated. The integrated cross sections for AB --> J/Psi (Psi')X for p-A and A-B collisions and the dependence on transverse energy for S-U and Pb-Pb can be described quantitatively with…
The gluon distribution of a nucleon propagating through a nucleus can change depending on how far the penetration depth is. It is a nonperturbative process that we describe by an evolution equation. The kernel of the integral equation is to be determined by a phenomenological study of J/psi suppression in pA collision. The data of E866 on alpha(x_F) shows significant dependence on x_F at large x_F. It presents a feature that has not been explained by any hadronic absorption model. We show that gluon depletion is a simple mechanism that can account for it. The result has far-reaching implicatio…
A kinetic equation approach is applied to model anomalous J/psi suppression at RHIC and SPS by absorption in a hadron resonance gas which successfully describes statistical hadron production in both experiments. The puzzling rapidity dependence of the PHENIX data is reproduced as a geometric effect due to a longer absorption path for J/psi production at forward rapidity.
In the field theoretical Glauber-Gribov framework in the eikonal approximation, we show that, in hadron-nucleus collisions in the high-energy limit and under especific conditions, the rescattering contributions to the J/psi production cross-section vanish, leading to an A^1 dependence on the atomic number A -- except for nuclear effects in the nucleus structure function, the so-called shadowing. We show that the RHIC data on $J/ψ$ production in d-Au collisions can be described with nuclear shadowing alone (sigma_{abs} = 0). The corresponding results for Au-Au collisions are also presented and …
Statistical QCD predicts that strongly interacting matter will become deconfined at high temperatures and/or densities. The aim of high energy nuclear collisions is to study the onset of deconfinement and the properties of deconfined media in the laboratory. Hence it is essential to define an unambiguous and experimentally viable probe for deconfinement. Twelve years ago, T. Matsui and I proposed that \J~production should constitute such a probe \cite{M&S}, and I want to sketch here rather briefly the evolution of this idea in the light of subsequent experimental and theoretical work.
We evaluate the transverse momentum spectrum of J/Psi (up to semi-hard momenta) in pA and AA collisions taking into account only the initial state effects, but resumming them to all orders in α_s^2 A^{1/3}. In our previous papers we noticed that cold nuclear matter effects alone could not explain the experimental data on rapidity and centrality dependencies of the J/Psi yield in AA collisions indicating the existence of an additional suppression mechanism. Our present calculations indicate that the discrepancy persists and even increases at semi-hard transverse momenta, implying a significant …
We calculate the inclusive J/Psi production in heavy ion collisions including the effects of gluon saturation in the wave functions of the colliding nuclei. We argue that the dominant production mechanism in proton--nucleus and nucleus--nucleus collisions for heavy nuclei is different from the one in hadron-hadron interactions. We find that the rapidity distribution of primary J/Psi production is more peaked around midrapidity than the analogous distribution in elementary pp collisions. We discuss the consequences of this fact on the experimentally observed J/Psi suppression in Au-Au collision…
We evaluate the Cold Nuclear Matter effects on J/psi production in pPb and PbPb collisions at the current LHC energy, taking into account the gluon shadowing and the nuclear absorption. We use the complete kinematics in the underlying 2 to 2 partonic process, namely $g+g \to \jpsi + g$ as expected from LO pQCD. The resulting shadowing is responsible for a large J/psi suppression in pPb and PbPb, and shows a strong rapidity dependence.
The measured ratios $R(x,A_1/A_2)$ for $J/Ψ$, $Ψ'$ and $μ^+μ^-$ production on two different targets $A_1, A_2$ as a function of the fractional momentum $x$ of the final state are well fit with a very simple functional form having three adjustable parameters. An empirical relation is found between the three parameters of the fit. The deduced $J/Ψ$ absorption cross sections $σ_{abs}$ cluster around two values of which only $σ_{abs} = 5.8 \pm 0.2$ mb seems acceptable.
