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Baoyi Chen
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This work studies the thermal production of $J/psi$ and $psi(2S)$ with Boltzmann transport model in the Quark Gluon Plasma (QGP) produced in $sqrt{s_{NN}}=5.02$ TeV Pb-Pb collisions. $J/psi$ nuclear modification factors are studied in details with the mechanisms of primordial production and the recombination of charm and anti-charm quarks in the thermal medium. $psi(2S)$ binding energy is much smaller in the hot medium compared with the ground state, so $psi(2S)$ with middle and low $p_T$ can be mainly thermally regenerated in the later stage of QGP expansions which enables $psi(2S)$ inherit larger collective flows from the bulk medium. We quantitatively study both nuclear modification factors of $J/psi$ and $psi(2S)$ in different centralities and transverse momentum bins in $sqrt{s_{NN}}=5.02$ TeV Pb-Pb collisions.
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Using the EPOS3 model with UrQMD to describe the hadronic phase, we study the production of short-lived hadronic resonances and the modification of their yields and $p_{T}$ spectra in p-Pb collisions at $sqrt{s_{NN}}$ = 5.02 TeV. High-multiplicity p-Pb collisions exhibit similar behavior to mid-peripheral Pb-Pb collisions at LHC energies, and we find indications of a short-lived hadronic phase in p-Pb collisions that can modify resonance yields and $p_{T}$ spectra through scattering processes. The evolution of resonance production is investigated as a function of the system size, which is related to the lifetime of the hadronic phase, in order to study the onset of collective effects in p-Pb collisions. We also study hadron production separately in the core and corona parts of these collisions, and explore how this division affects the total particle yields as the system size increases.
Direct photon spectra and elliptic flow v2 in heavy-ion collisions at RHIC and LHC energies are investigated within a relativistic transport approach incorporating both hadronic and partonic phases - the Parton-Hadron-String Dynamics (PHSD). The results suggest that a large v2 of the direct photons - as observed by the PHENIX Collaboration - signals a significant contribution of photons produced in interactions of secondary mesons and baryons in the late stages of the collision. In order to further differentiate the origin of the direct photon azimuthal asymmetry, we compare our predictions for the centrality dependence of the direct photon yield to the recent measurements by the PHENIX Collaboration and provide predictions for Pb+Pb collisions at LHC energies with respect to the direct photon spectra and v2(pT) for 0-40% centrality.
We present a systematic study of the correlators used experimentally to probe the Chiral Magnetic Effect (CME) using the Anomalous Viscous Fluid Dynamics (AVFD) model in Pb--Pb and Xe--Xe collisions at LHC energies. We find a parametrization that describes the dependence of these correlators on the value of the axial current density ($n_5/mathrm{s}$), which dictates the CME signal, and on the parameter that governs the background in these measurements i.e., the percentage of local charge conservation (LCC) within an event. This allows to deduce the values of $n_5/mathrm{s}$ and the LCC percentage that provide a quantitative description of the centrality dependence of the experimental measurements. We find that the results in Xe--Xe collisions at $sqrt{s_{mathrm{NN}}} = 5.44$~TeV are consistent with a background only scenario. On the other hand, the model needs a significant non-zero value of $n_5/mathrm{s}$ to match the measurements in Pb--Pb collisions at $sqrt{s_{mathrm{NN}}} = 5.02$~TeV.
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 $rm J/psi$ shows an increasing trend with event multiplicity. In the present contribution, we discuss the energy and multiplicity dependence of charmonium production to understand the effects of MPI on charmonium production.
The freezeout conditions in proton-proton collisions at $sqrt{s_{textrm{NN}}}= 200$, $900$ and $7000$ GeV have been extracted by fits to the mean hadron yields at mid-rapidity within the framework of the statistical model of an ideal gas of hadrons and resonances in the grand canonical ensemble. The variation of the extracted freezeout thermal parameters and the goodness of the fits with $sqrt{s_{textrm{NN}}}$ are discussed. We find the extracted temperature and baryon chemical potential of the freezeout surface to be similar in p+p and heavy ion collisions. On the other hand, the thermal behaviour of the strange hadrons is qualitatively different in p+p as compared to A+A. We find an additional parameter accounting for non-equilibrium strangeness production is essential for describing the p+p data. This is in contrast to A+A where the non-equilibrium framework could be successfully replaced by a sequential and complete equilibrium model with an early freezeout of the strange hadrons.
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