Effects of quark-gluon plasma and hadron gas on charmonium production at energies available at the CERN Super Proton Synchrotron and the Facility for Antiproton and Ion Research

The production of charmonium in heavy ion collisions is investigated based on the Boltzmann-type transport model for charmonium evolution and the 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 negligible at the Super Proton Synchrotron (SPS) and the Facility for Antiproton and Ion Research (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 necessary for the data. This means there should be QGP produced at central collisions, and no QGP produced at peripheral collisions at SPS energy. Predictions are also made at FAIR $\sqrt{s_{NN}}=7.7$ GeV Au+Au collisions.

Figure 1

Comparision between temperature evolution at the SPS and FAIR. HG is for the hadron gas. The temperature is at the center $\left(r=0\right)$ of the medium with fixed impact parameter $\mathbf{b}=0$.

Figure 2

Lifetimes of different charmonium states with temperature in QGP and hadron gas $\left({\mu }_B=0\right)$. The velocity of the medium is taken as $v=0.5$, and the transverse momentum of charmonium is taken as a typical value $p_{\mathrm{\Psi }}=1$ GeV/c, with the same direction as the velocity of the medium.

Figure 3

Normalized distribution of charm number as a function of transverse momentum at the FAIR and SPS simulated by PYTHIA.

Figure 4

Charmonium suppression as a function of transverse energy $E_t$ in $\sqrt{s_{NN}}=17.3$ GeV Pb+Pb collisions. Dotted line only includes nucleon absorption. Black dashed line includes QGP suppression; red solid line includes effects of both QGP and hadron gas. Blue solid line assumes no existence of QGP and only includes the contribution of hadron gas. All lines include effects of nucleon absorption. Yellow solid line is for the charmonium regeneration from the Langevin equation. Experimental data are from [13, 53].

Figure 5

Average transverse momentum squared of charmonium $\langle p_t^2\rangle$ as a function of transverse energy $E_t$ (GeV) in $\sqrt{s_{NN}}=17.3$ GeV Pb+Pb collisions. Dotted line only includes nucleon absorption. Black dashed line includes the effect of QGP; red solid line includes effects of both QGP and hadron gas. Blue solid line assumes no existence of QGP and only includes the contribution of hadron gas. All the lines include effects of nucleon absorption. Experimental data are from [28, 54].

Figure 6

Charmonium nuclear modification factor $R_{AA}$ as a function of the number of participants in $\sqrt{s_{NN}}=7.7$ GeV Au+Au collisions. Black dotted line includes only nuclear absorption; red solid line also includes the effects of QGP and hadron phase. Blue solid line assumes no existence of QGP, and charmonia only suffer suppression from nuclear absorption and hadron phase.

Figure 7

Charmonium average transverse momentum squared $\langle p_t^2\rangle$ as a function of the number of participants in $\sqrt{s_{NN}}=7.7$ GeV Au+Au collisions. Black dotted line includes only nuclear absorption; red solid line also includes the effects of QGP and hadron phase. Blue solid line assumes no existence of QGP, and charmonia only suffer suppression from nuclear absorption and hadron phase.