The splitting of directed flow for identified light hadrons (KK and pp) and strange baryons (Ξ\Xi and Ω\Omega) in Au+Au collisions at STAR

The first measurements for rapidity-odd directed flow of $\Xi$ and $\Omega$ in Au+Au collisions at $\sqrt{s_{\mathrm {NN}}}=$ 27 and 200 GeV are reported. The coalescence sum rule is examined with various combinations of hadrons where all constituent quarks are produced, such as K^{\!^-}\!\!({ \bar{u}}{s}), $\bar{p}({\bar{u}\bar{u}}{\bar{d}})$, $\bar{\Lambda}(\bar{u}\bar{d}\bar{s})$, $\phi({s}{\bar{s}})$, $\bar{\Xi}^{+}(\bar{d}\bar{s}\bar{s})$, ${\Omega}^{-}(sss)$, and $\bar{\Omega}^{+}(\bar{s}\bar{s}\bar{s})$. For such combinations, a systematic violation of the sum rule is observed with increasing difference in the electric charge and the strangeness content of the combinations. Measurements are compared with the calculations of A Multi-Phase Transport (AMPT) model and Parton-Hadron String Dynamics (PHSD) model with electromagnetic (EM) field. The PHSD model with EM field agrees with the measurements within uncertainties.Comment: Proceedings of Quark Matter 202

Heavy flavour Langevin diffusion with the chromo-electromagnetic field fluctuations in the quark-gluon plasma

The chromo-electromagnetic field is produced due to the motion of partons in a quark-gluon plasma created by relativistic heavy-ion collisions. The fluctuations in the produced chromo-electromagnetic field are important, since they cause heavy quarks to gain energy in the low velocity limit. We study the effect of such fluctuations on heavy quark diffusion in quark-gluon plasma within the framework of Langevin dynamics under the background matter described by the ($3+1$)-dimensional relativistic viscous hydrodynamics. Theoretical calculations of the nuclear modification factor ($R_{AA}$) of heavy mesons ($D$ and $B$ mesons), with the effect of these fluctuations, are compared with experimental measurements in $Au-Au$ collisions at $\sqrt{s_{NN}} = 200$ GeV by the STAR experiment at the BNL Relativistic Heavy Ion Collider (RHIC) and $Pb-Pb$ collisions at $\sqrt{s_{NN}} = 2.76$ and $5.02$ TeV by the ALICE and CMS experiments at the CERN Large Hadron Collider (LHC). We find a significant effect of these fluctuations in describing the the measured $R_{AA}$ of $D$ and $B$ mesons in both RHIC and LHC energies

Production of He-4 and (4) in Pb-Pb collisions at root(NN)-N-S=2.76 TeV at the LHC

Results on the production of He-4 and (4) nuclei in Pb-Pb collisions at root(NN)-N-S = 2.76 TeV in the rapidity range vertical bar y vertical bar <1, using the ALICE detector, are presented in this paper. The rapidity densities corresponding to 0-10% central events are found to be dN/dy4(He) = (0.8 +/- 0.4 (stat) +/- 0.3 (syst)) x 10(-6) and dN/dy4 = (1.1 +/- 0.4 (stat) +/- 0.2 (syst)) x 10(-6), respectively. This is in agreement with the statistical thermal model expectation assuming the same chemical freeze-out temperature (T-chem = 156 MeV) as for light hadrons. The measured ratio of (4)/He-4 is 1.4 +/- 0.8 (stat) +/- 0.5 (syst). (C) 2018 Published by Elsevier B.V.Peer reviewe

Study of Inclusive b-Jet Production in ALICE Experiment at LHC

The relativistic heavy-ion collisions produce a hot and dense deconfined state of QCD matter, called quark-gluon plasma (QGP). The characterization of this deconfined QCD matter is important to understand the fundamental thermodynamic and transport properties of it and how the constituents of it interact among themselves. Amongst many, one of the crucial probes to characterize the QCD matter is the heavy quark jets (charm jets, bottom jets (b-jets)), mainly produced in the primordial hard scatterings in the collisions. The measurement of b-jet production in p-Pb collisions addresses several key points like pQCD production cross-section, cold nuclear matter effect and base line for nucleus-nucleus collisions. Apart from these, the b-jet measurement in p–Pb collisions is interesting to investigate the interplay between heavy quark jets and the nuclear environment. The main focus of the thesis is to measure the bottom quark jet (b-jet) production in p-Pb collisions at √sNN = 5.02 TeV in the ALICE experiment at the LHC. We use the anti-kT jet finding algorithm with jet resolution parameter R = 0.4, as implemented in the FastJet package. The secondary vertices are searched within the reconstructed jets and the properties (large decay lengths) of the secondary vertices are used to tag the b-jets among other flavor jets. In order to obtain the b-jet yields, the tagged jets yields are corrected for tagging efficiency and purity, obtained from Monte Carlo simulations and data driven approach. Finally the b-jet yields are corrected for detector effects using Unfolding method and the systematic uncertainties are estimated. The measured pT-differential production cross section for b-jets in p-Pb collisions at √sNN = 5.02 TeV has been compared with NLO pQCD calculations (POWHEG+PYTHIA). The measurement of b-jet cross-section agrees well with the NLO pQCD calculations within the experimental and theoretical uncertainties. Apart from the experimental measurements, the thesis includes the phenomenological study of heavy quark propagation and chromo-electromagnetic field fluctuations present in the QGP medium. We estimate the effect of the color field fluctuations on the heavy quark transport coefficients (drag and diffusion coefficient), shear viscosity to entropy density ratio (η/s) of the QGP; and nuclear modification factors (RAA) of open charm (D mesons), open beauty mesons (B mesons) and hidden charm (J/Ψ) mesons. We find that these fluctuations result a reduction of the drag and diffusion coefficients of heavy quarks, as these fluctuations cause heavy quarks to gain energy. We also observe that the value of η/s of the QGP medium increases with the inclusion of these fluctuations and make the calculation of η/s closer to the value obtained in lattice QCD (LQCD) and functional renormalization group calculations. The calculated RAA of the heavy-flavor mesons can describe the measured RAA of D-mesons and B-mesons at the CMS and the ALICE experiments within their uncertainties, when the effect of these fluctuations is included along with the energy loss processes

Effect of thermal gluon absorption and medium fluctuations on heavy flavour nuclear modification factor at RHIC and LHC energies

The presence of thermal gluons reduces the stimulated gluon emission off a heavy quark propagating in the quark-gluon plasma (QGP) while absorption causes reduction of the radiative energy loss. On the other hand, the chromo-electromagnetic field fluctuations present in the QGP lead to collisional energy gain of the heavy quark. The net effect of the thermal gluon absorption and field fluctuations is a reduction of the total energy loss of the heavy quark, prominent at the lower momenta. We consider both kind of the energy gains along with the usual losses, and compute the nuclear modification factor ($$R_{AA}$$) of heavy mesons, viz., D and B mesons. The calculations have been compared with the experimental measurements in Au–Au collisions at $$\sqrt{s_{NN}} = 200$$ GeV from STAR and PHENIX experiments at the RHIC and Pb–Pb collisions at $$\sqrt{s_{NN}} = 2.76$$ TeV and 5.02 TeV from CMS and ALICE experiments at the LHC. We find a significant effect of the total energy gain due to thermal gluon absorption and field fluctuations on heavy flavour suppression, especially at the lower transverse momenta

Measurements of heavy-flavor jets with ALICE at the LHC

Heavy quarks created in ultra-relativistic heavy-ion collisions are mostly produced in hard QCD processes during the early stages of the reaction. They interact with the hot and cold nuclear matter throughout the evolution of the medium via semi-hard and soft processes such as energy loss via gluon radiations and collisions. Nuclear modification of heavy flavors in p-A systems provides insight into cold nuclear matter effects such as (anti)shadowing and $k_T-$ broadening, and serves as a baseline for A-A studies. In addition to that the fully reconstructed heavy-flavor jets provide additional information on the flavor (or mass) dependence of fragmentation, color charge effects as well as insight into the contribution of late gluon splitting. In this contribution, we present the measurements of $b$-jet production in p–Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV and $c$-jet production in pp, p–Pb and Pb–Pb collisions measured by the ALICE experiment at the LHC. The measurements of the nuclear modification factors for $c$-jet in p–Pb and Pb–Pb collisions are also presented. The experimental measurements are compared with the results from Monte Carlo event generators (PYTHIA 6, PYTHIA 8 and Herwig 7) and the NLO pQCD calculations (POWHEG+PYTHIA6). We find good agreement of the measurements with the results from Monte Carlo event generators and from NLO pQCD calculations.Heavy quarks created in ultra-relativistic heavy-ion collisions are mostly produced in hard QCD processes during the early stages of the reaction. They interact with the hot and cold nuclear matter throughout the evolution of the medium via semi-hard and soft processes such as energy loss via gluon radiations and collisions. Nuclear modification of heavy flavors in p-A systems provides insight into cold nuclear matter effects such as (anti)shadowing and $k_{T}$-broadening, and serves as a baseline for A-A studies. In addition to that the fully reconstructed heavy-flavor jets provide additional information on the flavor (or mass) dependence of fragmentation, color charge effects as well as insight into the contribution of late gluon splitting. In this contribution, we present the measurements of $b$-jet production in p-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV and $c$-jet production in pp, p-Pb and Pb-Pb collisions measured by the ALICE experiment at the LHC. The measurements of the nuclear modification factors for $c$-jet in p-Pb and Pb-Pb collisions are also presented. The experimental measurements are compared with the results from Monte Carlo event generators (PYTHIA 6, PYTHIA 8 and Herwig 7) and the NLO pQCD calculations (POWHEG+PYTHIA6). We find good agreement of the measurements with the results from Monte Carlo event generators and from NLO pQCD calculations

Heavy flavour Langevin diffusion with the chromo-electromagnetic field fluctuations in the quark–gluon plasma

The chromo-electromagnetic field is produced due to the motion of partons in a quark–gluon plasma created by relativistic heavy-ion collisions. The fluctuations in the produced chromo-electromagnetic field are important, since they cause heavy quarks to gain energy in the low velocity limit. We study the effect of such fluctuations on heavy quark diffusion in quark–gluon plasma within the framework of Langevin dynamics under the background matter described by the ($$3+1$$)-dimensional relativistic viscous hydrodynamics. Theoretical calculations of the nuclear modification factor ($$R_{AA}$$) of heavy mesons (D and B mesons), with the effect of these fluctuations, are compared with experimental measurements in Au–Au collisions at $$\sqrt{s_{NN}} = 200$$ GeV by the STAR experiment at the BNL Relativistic Heavy Ion Collider (RHIC) and Pb–Pb collisions at $$\sqrt{s_{NN}} = 2.76$$ and 5.02 TeV by the ALICE and CMS experiments at the CERN Large Hadron Collider (LHC). In addition to that, the elliptic flow ($$v_2$$) of D-meson has been calculated in the same framework for Pb–Pb collisions at $$\sqrt{s_{NN}} = 2.76$$ and compared with ALICE measurements. We find a significant effect of these fluctuations in describing the measured $$R_{AA}$$ and $$v_2$$ of heavy flavour mesons at both RHIC and LHC energies