The gluon density in nuclei, G^A(x), is poorly constrained at all x from the current DIS and Drell-Yan data. In this paper, we point out that J/psi production measured in proton-nucleus collisions at sqrt(s)=38.8 GeV by the E866 collaboration puts stringent constraints on the x-dependence of the G^W/G^Be ratio in the x=0.02-0.1 range. The E866 data suggest a rather mild x-dependence of G^W/G^Be, and consequently tend to favour DS and HKM sets, rather than the DSg, EKS, and EPS parametrizations which exhibit a large shadowing and anti-shadowing.
The transverse mass spectra of Omega, J/psi and psi' in Pb+Pb collisions at 158 AGeV are studied within a hydrodynamical model of the quark gluon plasma expansion and hadronization. The model reproduces the existing data with the common hadronization parameters: temperature T=T_H = 170 MeV and average collective transverse velocity v_T = 0.2.
We consider a novel mechanism for J/Psi production in nuclear collisions arising due to the high density of gluons. We calculate the resulting J/Psi production cross section as a function of rapidity and centrality. We evaluate the nuclear modification factor and show that the rapidity distribution of the produced J/Psi's is significantly more narrow in AA collisions due to the gluon saturation effects. Our results indicate that gluon saturation in the colliding nuclei is a significant source of J/Psi suppression that can be disentangled from the quark-gluon plasma effects.
Exclusive J/psi production, gamma* p -> J/psi p, offers a unique opportunity to determine the gluon density of the proton in the small x domain. We use the available HERA data to determine the gluon distribution in the region 10^{-4} <~ x <~ 10^{-2} and 2 <~ Q^2 <~ 10 GeV^2, where the uncertainty on the gluon extracted from the global parton analyses is large. The gluon density is found to be approximately flat at the lower scale; it is compared with those of recent global analyses.
Our approach to low-x deep inelastic scattering based on the ell-perp factorization of perturbative QCD (the color-dipole picture) yields parameter-free absolute predictions for J/Psi production. The connection of J/Psi production to the low-x saturation scale and to the gluon structure function is clarified.
We consider a contribution to J/psi hadroproduction in which the meson production is mediated by three-gluon partonic state, with two gluons coming from the target and one gluon from the projectile. This mechanism involves double gluon density and thus it enters at a non-leading twist, but it is enhanced at large energies due to large double gluon density at small x. The three-gluon contribution to J/psi hadroproduction is calculated within perturbative QCD in the k_T factorization framework, and it is found to provide a significant correction to the standard leading twist cross-section at the…
Presented here is a study of the large p_T J/psi production in hard diffractive process by the pomeron exchange at the Fermilab Tevatron. We find that this process (p\bar p \to p+J/psi+X) can be used to probe the gluon content of the pomeron and to measure the gluon fraction of the pomeron. And the diffractive direct J/psi production can also provide another crucial test for the color-octet fragmentation mechanism. Using the renormalised pomeron flux factor D\approx 1/9, the single diffractive J/psi production cross section at large p_T (\geq 8GeV) is found to be of order of 0.01 nb, and the r…
We investigate photo-production of vector mesons J/Psi and Psi(2s), based on both HERA and LHC data, using 2 fits of unintegrated gluon distributions. The latter are subject to non-linear Balitsky-Kovchegov evolution (Kutak-Sapeta gluon; KS) and linear next-to-leading order Balitsky-Kuraev-Fadin-Lipatov evolution (Hentschinski-Sabio Vera-Salas; HSS gluon) respectively. Apart from extending previous studies to the case of radially excited charmonium Psi(2s), we further use an improved set of charmonium wave functions and provide an estimate of the uncertainties associated with the HSS gluon. Wh…
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…
New, more precise data on diffractive J/psi photoproduction and on exclusive J/psi production in the process pp -> p + J/psi + p at the LHC allow a better constraint on the low-x gluon distribution in the domain of relatively low scales Q^2 ~ 2-6 GeV^2. We account for the `skewed' effect and for the real part of the amplitude, as well as for the absorptive corrections in the case of the exclusive process pp -> p + J/psi + p. The predictions for exclusive J/psi production at \sqrt{s}=8 and 14 TeV and for exclusive Upsilon(1S) production at 7, 8 and 14 TeV are also given. We present results at l…
The modifications induced in the calculation of the cross section of the diffractive process gamma gamma -> J/Psi J/Psi when the gluon propagator is changed are analyzed. Instead of the usual perturbative gluon propagator, alternative forms obtained using non-perturbative methods like Dyson-Schwinger equations are used to consider in a more consistent way the contributions of the infrared region. The result shows a reduction in the differential cross-section for low momentum transfer once compared with the perturbative result, to be confirmed with future experimental results from TESLA.
The eta(1760) may be significantly produced in J/Psi radiative decay. We deduce from experimental data that its branching ratio to two gluons is bounded, 0.4 +- 0.3 < BR(eta(1760) -> gg) < 0.9 +- 0.3, consistent with gluonic admixture. Moreover, the expectation that there should be an isoscalar analogue of the gluonic (hybrid) meson candidate pi(1800) is argued to reinforce hybrid admixture in eta(1760). Two-gluon coupling of hybrids is estimated in a spectator model to be considerably larger than that of quarkonium. In addition, the two-photon coupling of eta(1760) is estimated to be 1.4 +- 0…
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 …
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 summarize what is known about the transverse spatial distribution of gluons in the nucleon and its x-dependence from exclusive J/psi photo/electroproduction in e-p fixed-target and collider experiments (HERA H1 and ZEUS). This information can be used to predict the impact parameter dependence of the cross section for certain hard QCD processes (dijet production) in pbar-p and p-p collisions at the Tevatron and LHC.
Diffractive production of J/Psi particles by virtual photons on a proton target is studied with a view towards understanding two important corrections to the leading order result. First, the effect of Fermi motion of the heavy quarks is studied by performing a systematic expansion in the relative velocity, and a simple correction factor is derived. This is considerably less than estimated previously. Second, since the kinematics necessarily requires that non-zero momentum be transferred to the proton, off-forward gluon distributions are probed by the scattering process. To estimate the importa…
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…
Color-octet contributions to the associate J/psi+gamma hadroproduction are studied in detail, and found to be negligible, compared to the ordinary color-singlet contribution. Within the color-singlet model the J/psi+gamma production in the leading order is possible only through gluon-gluon fusion process. Therefore, the associate J/psi+gamma hadroproduction remains to be useful as a clean channel to probe the gluon distribution inside proton, to study heavy quarkonia production mechanism, and to find proton's spin structure.
We discuss the potential to constrain the small-$x$ PDFs using the exclusive production of heavy vector mesons. The calculation of $J/ψ$ and $Υ$ photoproduction at NLO in collinear factorisation is described. The different behaviour of the NLO corrections for $J/ψ$ and $Υ$ is highlighted and we outline what might be expected from the inclusion of these processes in a PDF fit.
We consider the contribution of radially excited 2^3P_{1,2} states to psi^prime production at the Tevatron energy. Production of these states via the conventional gluon fusion mechanism and via gluon and charm quark fragmentation processes is considered. We find that it is possible to account for the data on psi^prime production from the CDF experiment, by taking into account the decays of these 2^3P_{1,2} states into psi^prime.
We examine angular distributions of leptons arising from the decay of J/psi in inclusive hadroproduction. Taking into account feed-down contributions from chi_{1,2}, a flat distribution emerges without fine tuning parameters. Changes in the ratio of direct to total J/psi cross sections would change this distribution significantly. Such angular distributions are, therefore, confirmatory tests of the J/psi suppression signal for the production of a quark-gluon plasma. Related effects are predicted for the Upsilon.
We study the diffractive electroproduction of quarkonia from quark-antiquark-gluon states in the photon wave function. We show that these states contribute to the leading-power and leading-logarithm level. We suggest the measurement of J/psi production via inelastic diffraction to study color-transparency and color-opacity effects in the diffractive gluon distribution.
Using a nonrelativistic potential model, we calculate the cross section for the leading-order gluon dissociation of J/psi by including the full gluon wave function. We find that the resulting cross section as a function of gluon energy is reduced by about a factor of three at its maximum value compared to that calculated in the dipole approximation that is usually adopted in theoretical studies. The effect of the reduced cross section on the J/psi dissociation width at finite temperature is also discussed.
In order to get information about the polarized gluon distribution in a proton, we studied the electroproduction of ψ' in polarized electron and polarized proton collisions in the framework of the NRQCD factorization approach. The value of the cross section dΔσ/ dp_T^2 for color-octet mechanism is about 5 times larger than that for color-singlet one, and it might be another test of the color-octet model if the polarized gluon distribution Δg(x) is well known. Furthermore, we found that this reaction is quite effective for testing the model of gluon polarization by measuring the double spin asy…
Using a bound-state model of weakly bound gluons for glueballs made of two gluons and a natural generalization of the perturbative QCD formalism for exclusive hadronic processes, we present results for glueball production in radiative J/psi, Upsilon decays into several possible glueball states, including L \not= 0 ones. We perform a detailed phenomenological analysis, presenting results for the more favored experimental candidates and for decay angular distributions.
We compute the contributions to large-$p_T$ $J/ψ$ production at HERA coming from fragmentation of gluons and charm quarks. We find that the charm quark fragmentation contribution dominates over the direct production of $J/ψ$ via photon-gluon fusion at large-$p_T$, while the gluon fragmentation is negligibly small over the whole range of $p_T$. An experimental study of $p_T$ distributions of $J/ψ$ at HERA will provide a direct probe of the charm quark fragmentation functions.
The reaction γγ---> J/Psi J/Psi is discussed assuming dominance of the QCD BFKL pomeron exchange. We give prediction for the cross-section of this process for LEP2 and TESLA energies. We solve the BFKL equation in the non-forward configuration taking into account dominant non-leading effects which come from the requirement that the virtuality of the exchanged gluons along the gluon ladder is controlled by their transverse momentum squared. We compare our results with those corresponding to the simple two gluon exchange mechanism and with the BFKL pomeron exchange in the leading logarithmic app…
We investigate possible mass shift and width broadening of J/psi in hot gluonic matter using QCD sum rule. Input values of gluon condensates at finite temperature are extracted from lattice QCD data for the energy density and pressure. Although stability of the moment ratio is achieved only up to T/Tc ~ 1.05, the gluon condensates cause a decrease of the moment ratio, which results in change of spectral properties. Using the Breit-Wigner form for the phenomenological side, we find that mass shift of J/psi just above Tc can reach maximally 200 MeV and width can broaden to dozens of MeV.
Using the expression of the dynamical gluon mass obtained through the operator product expansion we discuss the relevance of gluon mass effects in the decays V -> hadrons (V = J/Psi, Upsilon). Relativistic and radiative corrections are also introduced to calculate alpha_s(m_c) and alpha_s(m_b) comparing them with other values available in the literature. The effects of dynamical gluon masses are negligible for Upsilon decay but important for J/Psi decay.
We consider the prompt hadroproduction of J/psi, psi' and the Upsilon (1S,2S,3S) states caused by the fusion of a symmetric colour-octet two-gluon state and an additional gluon. The cross sections are calculated in leading-order perturbative QCD. We find a considerable enhancement in comparison with previous perturbative QCD predictions. Indeed, the resulting cross sections are found to be consistent with the values measured at the Tevatron and RHIC, without the need to invoke non-perturbative `colour-octet' type of contributions.
We explore the effects of shadowing on inclusive J/psi and Upsilon(1S) production at AFTER@LHC. We also present the rates as a function of p_T and rapidity for p+Pb and Pb+p collisions in the proposed AFTER@LHC rapidity acceptance.
Gluons at small x in high-energy nuclei overlap in the longitudinal direction, so the nucleus acts as a single source of gluons, like higher Fock components in a single nucleon, which contribute to inelastic collisions with a high multiplicity of produced hadrons. This similarity helps to make a link between nuclear effects in pA and high-multiplicity pp collisions. Such a relation is well confirmed by data for the J/Psi production rate in high-multiplicity pp events measured recently in the ALICE experiment. Broadening of J/Psi transverse momentum is predicted for high-multiplicity pp collisi…
It is shown that the study of the ω-ρinterference pattern in the J/psi -> (rho+omega)eta -> pi+pi-eta decay provides evidence for the large (nearly 90 degrees) relative phase between the isovector one-photon and three-gluon decay amplitudes.
The only experimental information on the parton distribution of kaons was obtained from the scarce kaon-induced Drell-Yan cross section data. From these data, evidence for a valence $u$ quark distribution of kaon softer than that of pion was found. We study the feasibility to extract kaon's valence quark distribution via the existing kaon-induced J/psi production data. We compare the NA3 data on the K- / pi- and K+ / pi+ ratios for J/psi production on a platinum target with theoretical calculations based on the color-evaporation model. We show that the NA3 data on J/psi production provide an i…
We consider J/Psi meson production in $ep$ deep inelastic scattering in the colour singlet model using the k_T-factorization QCD approach. We investigate the z-, Q^2-, p_T^2-, y^*- and W-dependences of inelastic J/Psi production on different forms of the unintegrated gluon distribution. The p_T^2- and Q^2-dependences of the J/Psi spin aligment parameter alpha are presented also. We compare the theoretical results with recent experimental data taken by the H1 and ZEUS collaborations at HERA. It is shown that experimental study of the polarization J/Psi mesons at Q^2 < 1 {GeV}^2 is an additional…
The gluon-exchange contribution to $J/ψ$-nucleon scattering is shown to yield a sizeable scattering length of about -0.25 fm, which is consistent with the sparse available data. Hadronic corrections to gluon exchange which are generated by $ρπ$ and $D\bar D$ intermediate states of the $J/ψ$ are shown to be negligible. We also propose a new method to study $J/ψ$-nucleon elastic scattering in the reaction $π^+ d\to J/ψp p$.
We examine the so-called rho-pi puzzle of the psi(2S) decay by incorporating two inputs: One is the relative phase between the one-photon and the gluon decay amplitude, and the other is a possible anomaly in the inclusive nonelectromagnetic decay rate of psi(2S). We propose the possibility that in the psi(2S) decay a hadronic decay process of long distance origin is important in addition to the short-distance decay process. The amplitude of this additional process should nearly cancel the three-gluon amplitude in the exclusive psi(2S)---> 1-0- and turn the sum dominantly real in contrast to th…
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 derive the formulae for the cross section of J/Psi production in high energy pA and AA collisions taking into account the gluon saturation/color glass condensate effects. We then perform the numerical calculations of the corresponding nuclear modification factors and find a good agreement between our calculations and the experimental data on J/Psi production in dA collisions. We also observe that cold nuclear modification effects alone cannot describe the data on J/Psi production in AA collisions. Additional final state suppression (at RHIC) and enhancement (at LHC) mechanisms are required …
It is argued that the search of the J/psi --> f0(980)omega and J/psi --> a0(980)rho decays and the more precise definition of B(J/psi --> f0(980)phi) are the urgent purposes in the J/ψspectroscopy. It is shown that the study of the omega-rho0 interference pattern in the J/psi --> (ρ^0+ω)eta --> pi+pi-eta decay provides evidence for the large (nearly pi/2) relative phase between the isovector one-photon and three-gluon decay amplitudes .
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.
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.
The width of $B_c^+\to ψπ^+$ decay is calculated in the framework of factorization of a hard gluon exchange and a soft binding of quarks in the heavy quarkonium, so that ${\rm BR}(B_c^+\to ψπ^+) = 2.0\pm 0.5$ \%.
We study prompt J/psi-meson hadroproduction invoking the hypothesis of gluon Reggeization in t-channel exchanges at high energy and the factorization formalism of nonrelativistic quantum chromodynamics at the leading order in the strong-coupling constant alpha_s and the relative velocity of quarks v. The transverse-momentum distribution of direct and prompt J/psi-meson production measured at the Fermilab Tevatron fitted to obtain the nonperturbative long-distance matrix elements, which are used to predict prompt J/psi production spectra at the CERN LHC. At the numerical calculation, we adopt t…
We investigate $J/ψ$ photoproduction asymmetries in the framework of the NRQCD factorization approach. It is shown that the color octet contribution leads to large uncertainties in the predicted asymmetries which rules out the possibility to precisely measure the gluon polarization in the nucleon through this final state. For small values of the color octet parameters being compatible with $J/ψ$ photoproduction data it appears possible that a measurement of $J/ψ$ asymmetries could provide a new test for the NRQCD factorization approach, on one hand, or a measurement of the polarized gluon dist…
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…
In the framework of k_T-factorization QCD approach and the colour singlet model we consider J/ψinelastic photo- and leptoproduction processes at HERA. We investigate the dependences of the single differential and double differential cross section on different forms of the unintegrated gluon distribution. The z and p_T dependences of the spin aligment parameter αare presented also. Our theoretical predictions agree well with recent data taken by the H1 and ZEUS collaborations at HERA. It is shown that experimental study of the polarization J/ψmesons at low Q^2 < 1 GeV^2 is an additional test of…
We investigate $J/ψ$ photoproduction asymmetries in the framework of the NRQCD factorization approach. It is shown that the color octet contribution leads to large uncertainties in the predicted asymmetries which rules out the possibility to precisely measure the gluon polarization in the nucleon through this final state. For small values of the color octet parameters being compatible with $J/ψ$ photoproduction data it appears possible that a measurement of $J/ψ$ asymmetries could provide a new test for the NRQCD factorization approach, on one hand, or a measurement of the polarized gluon dist…
In the framework of kt-factorization approach, the production and polarization of prompt psi(2S) mesons in pp collisions at the LHC energies is studied. Our consideration is based on the non-relativistic QCD formalism for bound states and off-shell amplitudes for hard partonic subprocesses. The transverse momentum dependent (unintegrated) gluon densities in a proton were derived from Ciafaloni-Catani-Fiorani-Marchesini evolution equation or, alternatively, were chosen in accordance with Kimber-Martin-Ryskin prescription. The non-perturbative color-octet matrix elements were first deduced from …
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.
The $η$-$η^\prime$ pseudoscalar mixing angle and the gluonium content of the $η^\prime$ meson are deduced from an updated phenomenological analysis of $J/ψ$ decays into a vector and a pseudoscalar meson. In absence of gluonium, the value of the mixing angle in the quark-flavour basis is found to be $ϕ_P=(40.7\pm 2.3)^\circ$. In presence of gluonium, the values for the mixing angle and the gluonic content of the $η^\prime$ wave function are $ϕ_P=(44.6\pm 4.4)^\circ$ and $Z^2_{η^\prime}=0.29^{+0.18}_{-0.26}$, respectively. The newly reported values of $B(J/ψ\toρπ)$ by the BABAR and BES Collabora…
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…
To study the stability of heavy quarkonia in quark-gluon plasma, we use a color-singlet Q-Qbar potential determined previously to be a well-defined linear combination of the free energy F_1 and the internal energy U_1. Using the lattice gauge results of Kaczmarek et al., the dissociation temperatures of J/psi and chi_b in quenched QCD are found to be 1.62Tc and 1.18Tc respectively, in good agreement with spectral function analyses. The dissociation temperature of J/psi in full QCD with 2 flavors is 1.42Tc. Thus, the presence of dynamical quarks in full QCD lowers the dissociation temperature o…
We compute the relativistic corrections to the color-singlet contribution to gluon fragmentation into a J/psi at relative order v^4, making use of the nonrelativistic QCD (NRQCD) factorization approach. The corresponding full-QCD process exhibits infrared divergences that manifest themselves as single and double poles in epsilon in 4-2epsilon dimensions. We isolate the infrared-divergent contributions and treat them analytically. In the matching of full QCD to NRQCD, the pole contributions are absorbed into long-distance NRQCD matrix elements. The renormalizations of the ultraviolet divergence…
In spite of the sweeping coherence effects in high energy hadron and nuclei collisions, $k_T$-factorization can be recovered for the inclusive gluon production in $pA$ collisions at the leading logarithmic order. In open charm production at RHIC $k_T$-factorization holds numerically with about 10-20% accuracy. This allows to extrapolate the cold nuclear matter effect observed in light and charm meson production in $dA$ collisions to that in $AA$ ones. Unlike the open charm, the breakdown of factorization in $J/ψ$ production is severe. Indeed, already at the lowest order in gluon density the ma…
We calculate the Wilson coefficients of all dimension 6 gluon operators with non zero spin in the correlation function between two heavy vector currents. For the twist-4 part, we first identify the three independent gluon operators, and then proceed with the calculation of the Wilson coefficients using the fixed point gauge. Together with the previous calculation of the Wilson coefficients for the dimension 6 scalar gluon operators by Nikolaev and Radyushkin, our result completes the list of all the Wilson coefficients of dimension 6 gluon operators in the correlation function between heavy ve…
Experimental data on the onset of a so-called anomalous J/psi suppression in PbPb collisions at the SPS are considered in the framework of string percolation model. This onset is observed at a certain collision centrality, characterized by the number of nucleons-participants (Npart) related to the impact-parameter. Modified Bjorken formula calculations are performed for the local energy densities in AA collisions at different impact-parameters and with detailed account of the latest data available on the charged particles densities at midrapidity. Finally we compare variations of mean local en…
The production and space-time evolution of heavy quarks and J/psi in the quark gluon plasma is studied within the partonic transport model Boltzmann Approach to MultiParton Scatterings (BAMPS). This framework allows interactions among all partons: gluons, light quarks and heavy quarks. Heavy quarks, in particular, interact with the rest of the medium via binary scatterings with a running coupling and a more precise Debye screening which is derived from hard thermal loop calculations. We compare our results of the elliptic flow and nuclear modification factor not only to experimental data of he…
Nuclear shadowing and color glass condensate are possible only at sufficiently small x where parton clouds of different nucleons overlap in the longitudinal direction. Another condition vital for these effect, an overlap of partons in impact parameters, is not easy to fulfill for gluons which are located within small spots, as follows from the observed weakness of diffractive gluon radiation (smallness of the triple-Pomeron coupling). The predicted weakness of the leading twist gluon shadowing has been confirmed recently by data for J/Psi production and Cronin effect in d-Au collisions at RHIC…
Following HERA experiments our interest is focused, in the present paper, on charmonium production in lepton-proton collisions. Inelastic J/ψelectroproduction is quite difficult to be measured due to the low rates of events; almost all experimental studies are indeed performed in photoproduction regime. J/ψresonance is considered as the product of the hadronization of a c \bar{c} pair generated via boson-gluon fusion. The leading order contribution to the differential cross section, with respect to virtual photon-proton center of mass energy W and transferred four-momentum squared Q^2, is writ…
