Measurement Of D-meson Triggered Azimuthal Correlations And Study Of Anisotropic Flow Fluctuations At RHIC Energies

It is predicted that micro-seconds after the big bang the universe was filled with a phase of matter known as the quark-gluon plasma(QGP).The quark-gluon plasma is predicted by Quantum Chromodynamics and only exists for very high densities or temperatures.It was proposed that ultra-relativistic collisions between heavy ions can release the energy in a finite volume within a short period of time in which the conditions can be reached for creating a matter of deconfined quarks and gluons.The Relativistic Heavy Ion Collider(RHIC)was built to achieve enough high temperature and energy density to create the QGP.The study of high energy heavy-ion collisions at RHIC can give insights into the exploration of the stronglyinteracting quark-gluon plasma and QCD phase transition.Heavy quarks,produced at the early stages of the collision fully experienced the evolution of the QGP matter.Due to much larger mass than light quarks,heavy quarks are expected to thermalize more slowly than light quarks.These features make heavy quark a crucial probe for QGP properties in high energy heavy-ion collisions.At RHIC energies,heavy quarks are mostly produced in pairs through initial hard scatterings,early before the formation of the strongly interacting medium.Measurements of angular correlations triggered by heavy quarks in heavy-ion collisions can provide insights into the energy loss mechanism of heavy quarks in the QGP.Recent studies suggest that azimuthal correlations between heavy quark pairs uniquely probe the heavy quark-medium interaction dynamics,and therefore has the potential for distinguishing different energy loss mechanisms for heavy quarks.In p+p collisions,measurements of heavy-flavor triggered correlations allow us to test perturbative QCD(pQCD)calculations and provide references for studies in heavyion collisions.Direct comparison between heavy-flavor and light-flavor triggered correlations can also shed lights on the differences in fragmentation and hadronization between heavy and light quarks.In this thesis,we present the study of the azimuthal correlations between D*± mesons and charged hadrons(D*-h)measured by the STAR experiment in proton + proton collisions at center-of-mass energy of 500 GeV.Results at mid-rapidity in the transverse-momentum range 6?(?)?20 GeV/c are compared with light-hadron triggered correlations(h-h)and PYTHIA predictions.Through the extraction of the associated yield and width of the correlation signals,it is found that correlations of D*-h are systematically different from h-h on the near-side while compatible within uncertainties on the away-side.PYTHIA simulation with special tune well reproduce both D*-h and h-h experimental results.We also present an exploratory study of azimuthal correlations of D*+-D*- using the same experimental dataset.The background correlation method is verified with PYTHIA simulation.Experimental results are compared with model predictions.Besides the experimental study,in the framework of a multi-phase transport(AMPT)model,we investigate the anisotropic flow and initial partonic eccentricity fluctuations for Au+Au collisions at center-of-mass energy (?)= 200 GeV.The initial and final anisotropies in different order of harmonics are studied using participant and cumulant definitions in terms of second-,fourth-and sixth orders.Experimental results of flow anisotropies from cumulants are compared with model simulations.Experimental results are found generally well reproduced by the model including both parton cascade and hadronic re-scatterings.The ratio of the cumulant eccentricities ?{4}/?{2}and ?{6}/?{4}are studied in comparison with the ratio of the corresponding flow harmonics.The conversion coe cients(vn/?n)are explored up to fourth order harmonic based on cumulant method.Systematic studies on centrality,transverse momentum(pr)and pseudo-rapidity(?)dependencies of anisotropic flow and eccentricity fluctuations are presented.Relative fluctuation of triangular flow v3 is slightly centrality-dependent which is quite different from that of elliptic flow v2.It is observed that parton cascade has a large effect on the flow fluctuations,but hadronic scatterings make little contribution to the flow fluctuations,which indicates that flow fluctuations are mainly modified during partonic evolution stage.As in ideal hydrodynamics,initial eccentricities are expected to be closely related to the final flow harmonics in relativistic heavy-ion collisions,studies of the fluctuating initial condition in the AMPT model are crucial for the understanding of tomography properties of the initial source geometry.