Nucleon number dependence of the onset of anomalous J/psi suppression and the dynamics of nuclear collisions

We point out that data on the onset of anomalous J/psi suppression as a function of nucleon numbers A and B could provide information on the dynamics of nuclear interactions. In particular the models of anomalous J/psi suppression by Blaizot and Ollitrault (BO) and by Kharzeev, Lourenco, Nardi and Satz (KLNS) are based on different assumptions on the dynamics of nuclear collisions and lead to different predictions of the dependence of the onset of anomalous J/psi suppression on nucleon numbers of colliding nuclei. The data on this onset as function of A and B could become a tool for the study of the dynamics of nuclear collisions and bring further evidence on J/psi suppression by new form of hadronic matter, possibly Quark-Gluon Plasma. In particular we propose to study J/\psi suppression in A+Pb interaction with nucleon number of A between 58 and 73 or a bit higher.Comment: 10 pages, 5 Figure

Transverse energy dependence of J/Psi suppression in Au+Au collisions at RHIC energy

Prediction for transverse energy dependence of $J/\psi$ to Drell-Yan ratio in Au+Au collisions at RHIC energy was obtained in a model which assume 100% absorption of $J/\psi$ above a threshold density. The threshold density was obtained by fitting the NA50 data on $J/\psi$ suppression in Pb+Pb collisions at SPS energy. At RHIC energy, hard processes may be important. Prediction of $J/\psi$ suppression with and without hard processes were obtained. With hard processes included, $J/\psi$'s are strongly suppressed.Comment: 4 pages, 2 figures (revised version

Lockdown exit and control of the Covid-19 epidemic: group tests can be more effective

The lack of efficient mass testing tools for SARS-CoV-2 virus that causes Covid-19 has contributed to the accelerated spread of the epidemic. Infected people are unaware that they are spreading the disease during the incubation period as well as in asymptomatic cases or cases with mild symptoms. To limit the number of victims of the epidemic, the strategy adopted by most affected countries is therefore social distancing or complete lockdown, a strategy that can only be beneficial for a limited time, given its economic and social cost. Today, the most feasible way out of the stalemate requires widespread screening of the population. Such screening would make it possible to isolate infected people and allow others to leave the lockdown. However, production capacity for SARS-CoV-2 tests is limited. Although production is increasing, it will not allow for sufficiently systematic and frequent screening to permit the lifting of health restrictions. We here describe how the usefulness of each test can be amplified by applying it to the mixture of samples from several individuals. This technique, called group testing, has already been successfully applied on SARS-CoV-2. We show how the group-test method must be calibrated to maximize the usefulness of each available test

Comparison of Nuclear Suppression Effects on Meson Production at High p_T and p_L

The medium effect on the pion distribution at high $p_T$ in $AA$ collisions is compared to that of the pion distribution at high $p_L$ in $pA$ collisions. Both the suppression of the spectra and the energy losses of the measured pions are studied. Although the medium effect on $p_T$ is larger than on $p_L$, the difference is found surprisingly to be not as big as one would naively expect.Comment: 8 RevTex pages with 5 figure

Transverse Momentum Dependence of Anomalous J/\psi Suppression in Pb-Pb Collisions

The recently published data for $$ for $J/\psi$ production in Pb-Pb collisions at 158 A GeV are analyzed. For low values of transverse energy $E_t$, where normal suppression dominates, $(E_t)$ scales with the path length of the gluons which fuse to make the $J/\psi$. In the $E_t$ domain of anomalous suppression $(E_t)$ is found to rise linearly with the relative amount of anomalous suppression. This empirical law is reproduced within an analytically solvable transport model which allows high $p_t$ $J/\psi$'s to escape anomalous suppression. Interpreted in this way, the data for $(E_t)$ lead to an estimate of $t_A \sim 4$ fm/$c$ for the duration of anomalous suppression.Comment: 10 pages and 3 figure

Charmonium Suppression - Interplay of Hadronic and Partonic Degrees of Freedom

Last year the E866-group of the Fermilab measured the $x_F$ dependence of $J/\Psi$ and $\Psi'$ suppression in $pA$ collisions. We discuss two of the effects found in that experiment with regard to color coherence effects: the different suppression of the $J/\Psi$ and the $\Psi'$ at $x_F<0$ and the significant suppression of both at large $x_F$. The small $x_F$ regions is dominated by fully formed charmonium states and thus enables us to discuss the formation time and the cross section of the different charmonium states. In the large $x_F$ region the interaction of the charmonium states with nuclear matter has to be described by partonic degrees of freedom, because in that kinematic domain the formation time is much larger than the nuclear radii. The understanding of this region will be crucial for the interpretation of the data of the future heavy ion colliders RHIC and LHC.Comment: 4 pages, 1 table, 1 figure, Contribution to the Proceedings of the 15th Particles and Nuclei International Conference (PANIC 99), Uppsala, Sweden, June 10-16, 199

Nucleus-nucleus collisions: what we have learned from the heavy ion program at CERN

In the first part, I give a brief description of the quark-gluon plasma search at CERN and of some experimental results. In the second part, I review a dynamical model of nucleus-nucleus interactions and propose a physical interpretation of those results.Comment: LaTeX, 11 pages, uses fleqn.sty and espcrc2.sty. Figures available from the author. Invited talk at the XVth European Cosmic Ray Symposium, Perpignan (France), August 1996; to appear in the proceeding

Kinetic description of charmonium production in high-energy nuclear collisions

We study the evolution of charmonia as they collide with the constituents of the fireball produced in high-energy nucleus-nucleus collisions. The latter evolves in a manner controlled by the equation of state as given by lattice QCD, and is constructed in such a way that the observed hadronic spectra are correctly reproduced. A kinetic description of charmonium interactions with both quark-gluon and hadronic degrees of freedom allows to study in detail the evolution in different regimes, controlled by collision energy, kinematics and geometry. The data collected at the CERN-SPS accelerator are well described and new estimates for J/psi production at BNL-RHIC are presented.Comment: 19 pages, LaTeX, 13 .eps figure

Mott Effect and J/Psi Dissociation at the Quark-Hadron Phase Transition

We investigate the in-medium modification of pseudoscalar and vector mesons in a QCD motivated chiral quark model by solving the Dyson-Schwinger equations for quarks and mesons at finite temperature for a wide mass range of meson masses, from light (pi, rho) to open-charm (D, D*) states. At the chiral / deconfinement phase transition, the quark-antiquark bound states enter the continuum of unbound states and become broad resonances (the hadronic Mott effect). We calculate the in-medium cross sections for charmonium dissociation due to collisions with light hadrons in a chiral Lagrangian approach, and show that the D and D* meson spectral broadening lowers the threshold for charmonium dissociation by pi and rho meson impact. This leads to a step-like enhancement in the reaction rate. We suggest that this mechanism for enhanced charmonium dissociation may be the physical mechanism underlying the anomalous J/Psi suppression observed by NA50.Comment: 3 pages, 3 figures, uses EPJ style (included), contribution to the Proceedings of the International Conference on Quark Nuclear Physics, June 9 - 14, 2002, Juelich, Germany; 1 figure added, text adde