Recent experimental studies of the multiplicity dependence of heavy quark (HQ) production in proton-proton collisions at 7 TeV showed a strong non-linear increase of the HQ multiplicity as a function of the charged particle multiplicity. We try to understand this behavior using the EPOS3 approach. Two issues play an important role: multiple scattering, in particular its impact on multiplicity fluctuations, and the collective hydrodynamic expansion. The results are very robust with respect to many details of the modeling, which means that these data contain valuable information about very basic features of the reaction mechanism in proton-proton collisions.
We present the dependence of $D$ production on the charged particle multiplicity in proton-proton collisions at LHC energies. We show that, in a framework of source coherence, the open charm production exhibits a growth with the multiplicity which is stronger than linear in the high density domain. This departure from linearity was previously observed in the $J/ψ$ inclusive data from proton-proton collisions at 7 TeV and was successfully described in our approach. Our assumption, the existence of coherence effects present in proton-proton collisions at high energy, applies for high multiplicit…
We propose that the charged-particle multiplicity dependence of the charm-baryon-to-meson ratio observed in high-energy $pp$ collisions can be explained by canonical treatment of quantum charges in the statistical hadronization model (SHM). Taking the full particle listings of PDG complemented by additional charm-baryon states from relativistic quark model predictions, we evaluate the canonical partition function and the charm-hadron chemical factors that measure the canonical suppression arising from the requirement of strict conservation of quantum charges. We demonstrate that, while charm n…
Charm particle production in nucleus-nucleus collisions at the CERN SPS energies is considered within a statistical approach. Namely, the Statistical Model of the Early Stage is used to calculate mean multiplicity of charm particles in central Pb+Pb collisions. A small number of produced charm particles necessitates the use of the exact charm conservation law. The model predicts a rapid increase of mean charm multiplicity as a function of collision energy. The mean multiplicity calculated for central Pb+Pb collisions at the center of mass energy per nucleon pair $\sqrt{s_{NN}}=17.3$ GeV exceed…
At the LHC energies, the underlying observables are of major topic of interest in high multiplicity $p+p$ collisions. Multiple Parton Interactions (MPI) is one of them, in which several interactions occur in a single $p+p$ collision. It is believed that MPI is the main reason behind the high multiplicity in $p+p$ collisions at the LHC. It was believed that MPI has only effect to the soft particle production, but recent ALICE result reveals that it can also affect the hard-particle production. In such case, the self normalized yield of heavy particle like $\rm J/ψ$ shows an increasing trend wit…
In this note we provide a detailed derivation of the kinematic limit of the charm production in fixed-target experiments with the intrinsic charm coming from the target. In addition, we discuss the first measurement of charm quark production in the fixed-target configuration at the LHC.
In this paper we summarize our recent results for low energy associated charmonium production cross sections, using 1) crossing symmetry, and 2) an explicit hadronic model. These predictions are of relevance to the planned charmonium and charmonium hybrid production experiment PANDA at GSI.
By solving the rate equation in an expanding quark-gluon plasma, we study thermal production of charm quarks in central Pb+Pb collisions at the Future Circular Collider. With the charm quark production cross section taken from the perturbative QCD at the next-to-leading order, we find that charm quark production from the quark-gluon plasma can be appreciable compared to that due to initial hard scattering between colliding nucleons.
We present the first predictions for sub-threshold open charm and charmonium production in nuclear collisions. The production mechanism is driven by multi-step scatterings of nucleons and their resonance states, accumulating sufficient energy for the production of $J/Ψ$, $Λ_c + \overline{D}$ and $D+\overline{D}$. Our results are of particular importance for the CBM experiment at FAIR, as they indicate that already at the SIS100 accelerator one can expect a significant number of charmed hadrons to be produced. This opens new possibilities to explore charm dynamics and the formation of charmed n…
Open charm production during the equilibration of a gluon dominated parton plasma is calculated, with both the time-dependent temperature and parton densities given by a set of rate equations. Including pre-thermal production, the total enhancement of open charm production over the initial gluon fusion depends sensitively on the initial parton density and the effective temperature. The dependence of the pre-thermal charm production on the space-momentum correlation in the initial parton phase-space distribution is also discussed.
We study the centrality dependence to be expected if only charmonium production in the corona survives in high energy nuclear collisions, with full suppression in the hot, deconfined core. To eliminate cold nuclear matter effects as far as possible, we consider the ratio of charmonium to open charm production. The centrality dependence of this ratio is found to follow a universal geometric form, applicable to both RHIC and LHC in collisions at central and forward rapidities.
Both color screening and regeneration are hot medium effects on charmonium production in heavy ion collisions. While they affect in an opposite way the charmonium yield, their competition in transverse dynamics bring sensitivity to the ratio of averaged transverse momentum suqare for charmonium, which thus can reveal more nature of the QCD medium created from the collisions. We make an excitation analysis based on transport approach to illustrate such a picuture.
We study the effect of thermal charm production on charmonium regeneration in high energy nuclear collisions. By solving the kinetic equations for charm quark and charmonium distributions in Pb+Pb collisions, we calculate the global and differential nuclear modification factors $R_{AA}(N_{part})$ and $R{AA}(p_t)$ for $J/Ψ$s. Due to the thermal charm production in hot medium, the charmonium production source changes from the initially created charm quarks at SPS, RHIC and LHC to the thermally produced charm quarks at Future Circular Collider (FCC), and the $J/Ψ$ suppression ($R_{AA}<1$) observe…
The phenomenological analysis of various characteristics of $J/ψ$ and $D$ meson production in PbPb collisions at the center-of-mass energy 2.76 TeV per nucleon pair is presented. The data on momentum spectra and elliptic flow are reproduced by two-component model HYDJET++ including thermal and non-thermal charm production mechanisms. The significant part of $D$-mesons is found to be in a kinetic equilibrium with the created medium, while $J/ψ$-mesons are characterized by earlier (as compared to light hadrons) freeze-out.
Nuclear suppression of charmonium production in proton-nucleus interactions is poorly understood, what restrains our attempts to single out unusual effects in heavy ion collisions. We develop a phenomenological approach, based on the light-cone dynamics of charmonium production, which has much in common with deep-inelastic scattering and Drell-Yan lepton pair production. The key observation is the existence of a soft mechanism of heavy flavour production, which scales in the quark mass and dominates shadowing corrections and diffraction. It naturally explains the surprisingly strong nuclear su…
We study $b\bar{b}$ and $c\bar{c}$ production and the influence of nuclear shadowing at LHC and RHIC energies. We find a significant reduction in the production cross section of both charm and bottom at RHIC and LHC. Bound states such as $Υ$ and $J/Ψ$ are suppressed by this reduction in the charm production cross sections. Therefore, $J/Ψ$ suppression may not be useful as a signature for the quark gluon plasma.
The production of charmonium in heavy-ion collisions is investigated based on Boltzmann-type transport model for charmonium evolution and langevin equation for charm quark evolution. Charmonium suppression and regeneration in both quark-gluon plasma (QGP) and hadron phase are considered. Charm quarks are far from thermalization, and regeneration of charmonium in QGP and hadron gas is neglectable at SPS and FAIR. At peripheral collisions, charmonium suppression with hadron gas explains the experimental data well. But at central collisions, additional suppression from deconfined matter (QGP) is …
The production of particles with double, triple and hidden charm in heavy ion collisions is studied in the framework of the statistical coalescence model. According to the postulates of the model, the charm quark-antiquark pairs are created at the initial stage of a heavy ion reaction in hard parton collisions. The amount of charm is assumed to be unchanged at later stages. The charm (anti)quarks are distributed among different hadron species at hadronization according to the laws of statistical physics. Several approaches to the statistical treatment of charm hadronization are considered. The…
I discuss issues related to charmonium production, in view of physics possibilities at a 15 ... 30 GeV continuous beam electron facility. High energy photo- and hadroproduction of heavy quarkonia presents several challenges to QCD models concerning cross sections, polarization and nuclear target dependence. Theoretical approaches based on color evaporation as well as on color singlet and color octet mechanisms have met with both successes and failures, indicating that charmonium production is a sensitive probe of color dynamics. Experiments close to charm kinematic threshold will be sensitive …
Parameterizing the charm and anticharm quark momentum distributions by the Tsallis distribution, we study the nonequilibrium effect on the charmonium production rate in a quark-gluon plasma up to the next-to-leading order in perturbative QCD. We find that nonequilibrium charm and anticharm quarks suppress the charmonium production rate compared to that from equilibrated ones. We further show that the suppression factor calculated with the charm quark relaxation time, which has been frequently used in the literature, is close to our results.
To investigate a recent proposal that J/$ψ$ production in ultra-relativistic nuclear collisions is of thermal origin we have reanalyzed the data from the NA38/50 collaboration within a thermal model including charm. Comparison of the calculated with measured yields demonstrates the non-thermal origin of hidden charm production at SPS energy. However, the ratio $ψ^{'}$/(J/$ψ)$ exhibits, in central nucleus-nucleus collisions, thermal features which lead us to a new interpretation of open charm and charmonium production at SPS energy. Implications for RHIC and LHC energy measurements will be disc…
In these proceedings, we apply the recently developed S-ACOT-MPS factorization scheme at the next-to-leading order to prompt charm production at hadron colliders. It provides a good agreement with experimental data on charm meson production measured by LHCb at 7 and 13 TeV. The low-$p_T$ data are on the margins of the theoretical error bands, emphasizing the importance of including contributions beyond the next-to-leading order.
One of the most promising probes to study deconfined matter created in high energy nuclear collisions is the energy loss of (heavy) quarks. It has been shown in experiments at the Relativistic Heavy Ion Collider (RHIC) that even charm and bottom quarks, despite their high mass, experience a remarkable medium suppression in the Quark Gluon Plasma. In this exploratory investigation we study the energy loss of heavy quarks in high multiplicity proton-proton collisions at LHC energies. Although the colliding systems are smaller than compared to those at RHIC (p+p vs. Au+Au) the higher energy might…
We provide predictions for charmonium and open charm production in nuclear collisions at SPS/FAIR energies within the framework of the statistical hadronization model. The increasing importance at lower energies of Lambda_c production is demonstrated and provides a challenge for future experiments. We also demonstrate that, because of the large charm quark mass and the different timescales for charm quark and charmed hadron production, possible modifications of charmed hadrons in the hot hadronic medium do not lead to measurable changes in cross sections for D-meson production. A possible infl…
The effect of gluon shadowing on charm quark production in large impact parameter ultrarelativistic heavy ion collisions is investigated. Charm production cross sections are calculated for a range of non-central impact parameters which can be accurately inferred from the global transverse energy distribution. We show that charm production is a good probe of the local parton density which determines the effectiveness of shadowing. The spatial dependence of shadowing can only be studied in heavy ion collisions.
We discuss the production of charmonium states in antiproton-nucleus collisions at the $ψ'$ threshold. It is explained that measurements in $\bar p A$ collisions will allow to get new information about the strengths of the inelastic $J/ψN$ and $ψ'N$ interaction, on the production of $Λ_c$ and $\bar{D}$ in charmonium-nucleon interactions and for the first time about the nondiagonal transitions $ψ' N\to J/ψN$. The inelastic $J/ψ$-nucleon cross section is extracted from the comparison of hadron-nucleus collisions with hadron-nucleon collisions. Predictions for the ratio of $J/ψ$ to $ψ'$ yields in…
We study the strangeness and charm productions induced by the pion beam, i.e. the $π^-$p $\rightarrow$ $K^{*0}Λ$ and $π^-$p $\rightarrow$ $D^{*-}Λ_c^+$ reactions, based on two different theoretical frameworks: an effective Lagrangian method and a Regge approach. In order to estimate the magnitude of the charm production relative to that of the strangeness production, we assume that the coupling constants for the charmed meson and baryon vertices are the same as those for the strangeness channel. We found that the total cross section for the charm production was about $10^3 - 10^6$ times smalle…
Using an effective hadronic Lagrangian with physical hadron masses and coupling constants determined either empirically or from SU(4) flavor symmetry, we study the production cross sections of charm mesons from pion and rho meson interactions with nucleons. With a cutoff parameter of 1 GeV at interaction vertices as usually used in studying the cross sections for $J/ψ$ absorption and charm meson scattering by hadrons, we find that the cross sections for charm meson production have values of a few tenth of mb and are dominated by the s channel nucleon pole diagram. Relevance of these reactions …
Production of $c\bar c$ pairs in elementary hadron-hadron collisions is introduced in a simulation of relativistic heavy ion collisions. Coalescence of charmed quarks and antiquarks into various charmonium states is performed and the results are compared to PHENIX J$/ψ$ Au+Au data. The $χ$ and $ψ$' bound states must be included as well as the ground state J$/ψ$, given the appreciable feeding from the excited states down to the J$/ψ$ via gamma decays. Charmonium coalescence is found to take place at relatively late times: generally after $c$($\bar c$)-medium interactions have ceased. Direct pro…
The cross sections of the production of bound states with hidden charm in reactions induced by pions and photons are presented. To facilitate the experimental efforts to determine the $J/Ψ$-N interactions, we present results for $J/Ψ$ production on the deuteron.
We discuss aspects of the statistical hadronization model for the production of mesons with open and hidden charm in ultra-relativistic nuclear collisions. Emphasis is placed on what can be inferred from the dependence of the yield of charmonia on the number of participants in the collisions.
We study the production of charm mesons and other charm baryons from quark matter at CERN SPS and RHIC energies. Using quark coalescence models as hadronization mechanism, we predict particle ratios, absolute yields and transverse momentum spectra.
We discuss the production of charmonium in nuclear collisions within the framework of the statistical hadronization model. We demonstrate that the model reproduces very well the availble data at RHIC. We provide predictions for the LHC energy where, dependently on the charm production cross section, a dramatically different behaviour of charmonium production as a function of centrality might be expected. We extend our predictions for charm production towards the threshold energies, where charm is expected to be measured at the future FAIR facility.
