Elliptic Flow Ν2 Research Articles

Quarkonium measurements in nucleus-nucleus collisions with ALICE

Heavy quarks are produced in the early stages of nucleus-nucleus collisions and can therefore provide important insight into the Quark–Gluon Plasma (QGP). Quarkonia are proposed as crucial probes to study the QGP. The extent of the medium modification for heavy-quark quarkonium production in heavy-ion collisions is measured in terms of a nuclear modification factor RAA, defined as the quarkonium yield in heavy-ion collisions divided by the relative quarkonium cross section in pp collisions scaled by the nuclear overlap function. A possible path-length dependent quarkonium dissociation, as well as a contribution of (re-)generation of quarkonia from heavy quarks in the medium, would lead to an azimuthal anisotropy of quarkonium production relative to the reaction plane. In this contribution, the recent ALICE measurements of quarkonia in Pb–Pb collisions at sNN=5.02TeV will be discussed for both mid- and forward rapidity. The dependence of RAA on centrality and pT for J/ψ, ϒ(1S), ϒ(2S), as well as the J/ψ elliptic flow ν2 will be shown. Comparisons between the experimental data and the current theoretical model calculations will be also discussed.

Impact of Glasma on heavy quark RAA and ν2 in nucleus-nucleus collisions at LHC

We study the effect of the strong quasi-classical gluon field produced in the pre-thermal equilibrium stage of ultra-relativistic heavy ion collisions (RHICs) on the evolution of heavy quarks. It is shown that this field leads to an initial enhancement of the nuclear modification factor (RAA) of charm quarks at large pT. After the further evolution in the QGP phase, we find a larger interaction strength, which is necessary to obtain the RAA measured in experiments, compared to the standard drag and diffusion dynamics without the inclusion of this pre-thermal equilibrium stage. Moreover, we find a larger final elliptic flow ν2 is obtained, that is quite close to the experimental measurements.

Number of constituent quark scaling of elliptic flows in high multiplicity p-Pb collisions at [formula omitted

We briefly summarize our recent study on the number of constituent quark (NCQ) scaling of hadron elliptic flows in high multiplicity p-Pb collisions at sNN=5.02TeV. With the inclusion of hadron production via the quark coalescence model at intermediate pT, the viscous hydrodynamics at low pT, and jet fragmentation at high pT, our Hydro – Coal – Frag model provides a nice description of the pT-spectra and differential elliptic flow ν2(pT) of pions, kaons and protons over the pT range from 0 to 6 GeV. Our results demonstrate that including the quark coalescence is essential for reproducing the observed approximate NCQ scaling of hadron ν2 at intermediate pT in experiments, indicating strongly the existence of partonic degrees of freedom and the formation of quark-gluon plasma in high multiplicityp-Pb collisions at the LHC.

Transport properties from Charm to Bottom: pT suppression, anisotropic flow νn and their correlations to the bulk dynamics

We study the propagation of heavy quarks (HQs) in the quark-gluon plasma (QGP) by means of a relativistic Boltzmann transport (RBT) approach. The non-perturbative interaction between heavy quarks and light quarks is described by means of a quasi-particle approach able to describe simultaneously the experimental data for the nuclear suppression factor RAA and the elliptic flow ν2(pT) of D mesons from RHIC to LHC energies. In the same framework we predict the B meson nuclear modification factor at LHC. Finally, we discuss the relevance of initial state fluctuations that allows to extend the analysis to high order anisotropic flows νn(pT) as well as to investigate the role of QCD interaction in developing correlations between the light and the heavy flavour anisotropic flows.

QCD equation of state for heavy ion collisions**Supported by National Natural Science Foundation of China (11447121, 11475085, 11535005, 11690030), Fundamental Research Funds for the Central Universities (020414380074), Jiangsu Planned Projects for Postdoctoral Research Funds (1501035B) and Natural Science Foundation of Jiangsu Province (BK20130078, BK20130387)

In this work, we calculate the equation of state (EoS) of quark gluon-plasma (QGP) using the Cornwall-Jackiw-Tomboulis (CJT) effective action. We get the quark propagator by using the rank-1 separable model within the framework of the Dyson-Schwinger equations (DSEs). The results from CJT effective action are compared with lattice QCD data. We find that, when μ is small, our results generally fit the lattice QCD data when T > Tc, but show deviations at and below Tc. It can be concluded that the EoS of CJT is reliable when T > Tc. Then, by adopting the hydrodynamic code UVH2+1, we compare the CJT results of the multiplicity and elliptic flow ν2 with the PHENIX data and the results from the original EoS in UVH2+1. While the CJT results of multiplicities generally match the original UVH2+1 results and fit the experimental data, the CJT results of ν2 are slightly larger than the original UVH2+1 results for centralities smaller than 40% and smaller than the original UVH2+1 results for higher centralities.

Are flow measurements at RHIC reliable?

The measurements of collective flow effects in particle production have provided invaluable insights on the transport properties of the strongly interacting matter produced in relativistic heavy-ion collisions at RHIC. The detailed comparison of flow measurements from PHENIX and STAR experiments at RHIC have been presented and discussed. For elliptic flow ν2 of charged hadrons from Au+Au collisions at 200 GeV the two data sets overlap excellently for centralities > 20%, they increasingly diverge at small centralities, with a 30% difference between STAR an PHENIX in the 0-5% centrality bin. For ν3 values the agreement is much worse and coming from the difference in STAR measurements. More investigations are needed to understand the reason for such differences.

Open heavy-flavour measurements in pp and Pb-Pb collisions with ALICE at the LHC

We present an overview of measurements related to open heavy-flavour pro- duction with the ALICE experiment at the LHC. Studies are performed using single lep- tons (electrons at mid-rapidity and muons at forward-rapidity) and D mesons, which are reconstructed via their hadronic decay channels. The measured differential production cross sections in proton-proton collisions at √ s = 2.76 and 7 TeV are in agreement with perturbative QCD calculations. Results from Pb-Pb collisions at √ sNN = 2.76 TeV on the nuclear modification factor RAA are shown, along with the elliptic flow ν2.