Probing The Properties Of The QGP Via Multiparticle Azimuthal Correlations

Quantum chromodynamics(QCD)theory involved the strong interaction predicts a phase transition from hadron-state matter to a deconfined medium(Quark Gluon Plasma,QGP),in which the corresponding freedom degrees are of partonic nature.To achieve this restricted condition in which the phase transition implements,heavy-ion collisions at ultra-relativistic energies produce sufficiently high temperature or density in the lab-oratory and provide a unique opportunity to investigate the properties of the hot and dense QCD matter.Since the first circumstantial evidence that showed the quark-gluon plasma exists using lead-lead(Pb-Pb)collisions at(?)GeV from Super Pro-ton Synchrotron(SPS)at European Organization for Nuclear Research(CERN)and then gold-gold(Au-Au)collisions at(?)GeV from the Relativistic Heavy Ion Collider(RHIC)at Brookhaven National Laboratory(BNL),a sequence of surprising findings and observations revealing the properties of the QGP are achieved.Anisotropy flow,one of the observations,is coming from the pressure-driven ex-pansion and can be characterized by the Fourier coefficients vn in the azimuthal angle(?)distribution of the hadron yield.The anisotropies derived from the translation from initial spatial anisotropy into an azimuthal anisotropy in the momentum space of the produced hadrons.Heavy-flavor(charm and bottom)anisotropies are considered bet-ter candidates,which are restricted to the initial hard scatterings.This is because the mass of heavy-flavor quarks is larger than the typical temperature reached in the ambi-ent medium(mQ>>TQGP),and the anisotropy flow carries an important memory about early interaction.Multi-particle correlation technology is widely used in the calculation of anisotropic flows due to its unique advantages.Multi-particle correlations techniques involving four particles and more(v2{n},with n>4)are studied.Compared to the vn measurements from two-particle correlations,the four-particle correlations provide smaller non-flow effect,which contributes vn measurement.In addition,the event-by-event fluctuations of flow harmonics are recognized to influence the vn measurement.In this work,mul-tiparticle azimuthal correlations including one prompt D0 meson and other three light-flavor hadrons are measured in PbPb collisions at(?)TeV.The corresponding data is collected using Compact Muon Solenoid(CMS)detector at the CERN Large Hadron Collider(LHC)in 2018.The second-order Fourier coefficient(v2)of prompt D0 is extracted for the first time using four-particle correlations.If event-by-event fluctu-ations exist,the v2 from four-particle correlation(v2{4})will be less than the ones from two-particle correlations(v2{2}).In addition,the ratios of v2{4}/v2{2} of D0 meson are compared to those of light-flavor hadrons to disentangle the fluctuation source from the initial state or energy loss.The comparable amplitude suggests the contributions from fluctuations of initial geometric conditions are dominant.And the hints of split-ting of v2{4}/v2{2} ratios between charm mesons and light-flavor hadrons in the most central and most peripheral events suggest the influence of energy loss fluctuations.Multi-particle correlation is also a powerful tool to explore the underlying mecha-nism of particle production in hot QCD matter.In this work,two-particle angular cor-relations are applied in pp collisions at(?)TeV for all particle/anti-particle com-binations(pions,kaons,protons,and lambdas)using a multiphase transport(AMPT)model.In addition to being able to describe the angular correlation functions of meson-meson pairs,a large improvement for the angular correlations of baryon-baryon and antibaryon-antibaryon is achieved.Actually,it presents a challenge to Monte Carlo models(eg,PYTHIA,Perugia)for the baryon-baryon and antibaryon-antibaryon pairs,where a near-side depression structure is observed instead of a peak.We further find that a larger improvement is achieved by the AMPT model with new quark coalescence on the anticorrelation feature of baryon-baryon correlations.In addition,we also ex-tend the study to p-Pb,Pb-Pb and Au-Au collisions at BNL-RHIC and CERN-LHC energies.The results suggest the low pT baryon-baryon angular anticorrelations have a strong multiplicity dependence.