Jet Quenching Effect In Different Systems Of High-energy Nucleus Collisions

Quantum Chromodynamics(QCD),the basic theory describing the strong interactions of quarks and gluons,has two key features:quark confinement and asymptotic freedom.Quark confinement results in quarks and gluons trapped in hadrons,and individual quarks and gluons cannot be observed in the real world.Asymptotic freedom means that the larger the momentum transferred between quarks by gluons,the smaller the strong interaction between quarks,and the closer the behaviour of quarks is to that of free particles.In the extreme Relativistic Heavy-lon Collisions Experiment,the nucleus and even the nucleons in it are "smashed",and the heat energy converted from the huge kinetic energy is concentrated in a very small geometric space.At such extremely high temperature and density,the "color connect" between quarks is weak and can propagate beyond the nucleon's size,meaning that the confinement quarks in nucleons is released.A large number of quarks in nucleons released in heavy-ion collisions,undergoing a short period of strong interaction,a new state of matter,Quark-Gluon Plasma(QGP),is formed in where the energy is deposited.The discovery of this new form of matter and the study of its properties will have a profound impact on the understanding of the evolution of the universe,the formation and properties of stars,the micro-structure and interaction of matter and many other aspects.Therefore,the theoretical and experimental study of this new form of matter,creating in high-energy heavy-ion collisions,is an important research field in the frontier of high-energy nuclear physics.High energy partons(quarks or gluons)jet is the hard probe to explore the properties of created quark-gluon plasma in relativistic nuclear collisions.When an energetic jet transverses such high temperature and density matter,it will interact with the QGP medium via multiple scatterings and medium-induced gluon radiations and then lose its energy,leading to significant suppression effect on the yields of final state hadrons and jets of large transverse momentum pT.This effect is called jet quenching phenomenon.It has become an important means and method to study the formation and properties of quark-gluon plasma by using the related phys-ical phenomena caused by jets energy loss as the hard probe signals.Both Relativistic Heavy Ion Collider(RHIC)at Brookhaven National Laboratory(BNL)and the Large Hadron Collider(LHC)at European Organization for Nuclear Research(CERN)have performed a large number of extreme relativistic heavy-ion collisions experiments.Jet quenching phenomena observed in above experiments provide essential evidences for the formation of quark-gluon plasma.As the collision energies of heavy-ion collision experiments increase gradually at RHIC and the LHC,the accumulated experimental data become more and more abundant,and then the theoretical and experimental researches push the study of jet quenching into a quantitative era.Among them,the quantitative extraction of jet transport coefficient is considered to be an important goal of the jet quenching research.Besides,whether QGP is formed in the small system produced by p-Pb collisions has also attracted much attention.The main reason is that the similar behaviours of elliptic flow and triangular flow,even strangeness particles enhancements have been observed in p-Pb collisions as that in Pb-Pb collision large systems.Therefore,one has to wonder whether the QGP medium is produced in p-Pb collisions as that in Pb-Pb collisions.In fact,light nuclear collision experiments,such as O-O and Ar-Ar collisions,have also been discussed in the international experimental cooperation groups,and they bridge the gap between the p-Pb collision small system and the Pb-Pb collision large systems.In this work,based on the next leading order(NLO)perturbative quantum chromodynamics(pQCD)parton model and jet quenching theory model combined with hydrodynamic model describing the QGP space-time evolution,we performed an study for jet quenching effect in high-energy nuclear collision large and small systems and gave the system size dependence and medium temperature dependence of jet transport coefficient,reflecting the strengthen of jet quenching.We firstly studied the large transverse momentum leading hadrons nuclear modification factor RAA and elliptic flow coefficient v2 in heavy nucleus-nucleus collision large systems at RHIC and the LHC.By fitting RAA and v2 to experimental data simultaneously,we used a pa-rameter analysis method to extract the jet transport coefficient.Because of the different hot and density properties of QGP created in collision systems with different energies and centralities,and taking the temperature changes in the process of system evolution into account,we also performed quantitative analyses on the medium temperature dependence of jet transport coef-ficient.Since the simple assumption that the jet transport coefficient q is proportional to the medium temperature cubed cannot give well descriptions of the experimental data RAA and v2 simultaneously,we assume that q/T3 has two additional dependence on temperature,Linear or Gaussian,respectively.By simultaneous fitting RAA and v2 to experimental data,our numeri-cal results show that the peak of scaled q/T3 is near the critical temperature.Compared to the constant q/T3 case,such additional temperature dependence pushes the peak of jet energy loss rate to the critical temperature nearby and therefore strengthens the anisotropy of jet energy loss up to 10%manifested by our numerical results for v2 at high transverse momentum of hadrons.Taking the hadronic phase into account,the azimuthal anisotropy of final state hadrons will be further enhanced by 10%at RHIC and 5%at the LHC,relatively better in consistent with the experimental data.Secondly,in this work,we have studied the suppression effect of final state large pT sin-gle inclusive hadrons and di-hadrons in central Pb-Pb and Xe-Xe collision systems at the LHC.Within the NLO pQCD parton model combined with medium modified fragmentation functions,we have extracted the jet transport parameter q via single inclusive hadron suppression factor RAA and di-hadron suppression factor IAA.Our model can provide a consistent description for the suppressions of single hadron and dihadron productions in heavy nucleus-nucleus collisions at RHIC and the LHC energies.Numerical simulation results show that high pT single hadrons are mainly from the fragmentation of surface emission jets,while dihadron come from a combi-nation of surfacial and tangential jets as well as punching-through jets,which means on average in a.A-A event typically single hadron RAA is less than IAA,both of them reflecting the average jet quenching effect.Calculations give that q/T3=4.1?4.4 at T=378 MeV at RHIC and q/T3=2.6?3.3 at T=486 MeV at the LHC,which are consistent with the results from JET Collaboration.We also extracted the q/T3 in central Pb-Pb collisions at(?)=5.02 TeV and central Xe-Xe collisions at(?)=5.44 TeV via single hadron suppressions.With the extracted parameter values,we provide the predictions for the di-hadron suppression factors in both two collision systems.In addition,the ?-triggered hadron productions in p-Pb collision small system at the LHC energy would be also presented.We assume that a small droplet of QGP is created in 5.02 TeV p-Pb collisions.Then within NLO pQCD parton model combined medium modified fragmenta-tion function which considers the jet quenching effect and using the superSONIC hydrodynamic model describing the QGP space-time evolution,we have studied the ?-triggered hadron pro-duction suppression in p-Pb collisions at(?)=5.02 TeV.According to the simulation results from hydrodynamic model,the initial center temperature of created medium in central p-Pb col-lisions is similar to that of in central Au-Au collisions at 200 GeV,so that we use the similar q/T3 in 5.02 TeV central p-Pb collisions to that extracted in 200 GeV central Au-Au collisions.Within different collision centralities and with different trigger-? transverse momentum,we ex-amined that whether the ?-triggered hadron spectra is suppressed due to jet quenching effect and carefully analysed whether the enhancement caused by initial state cold nuclear anti-shadowing effect will cover up the jet quenching effect in 5.02 TeV p-Pb collisions.Numerical results for this scenario show that ?-hadron spectra at pT?=12-40 GeV/c are suppressed by 5-15%in the most central 0-10%p-Pb collisions at(?)=5.02 TeV.The suppression becomes weaker at higher transverse momentum of the ?-trigger.As a comparison to the small system,?-hadron suppression in Pb-Pb collisions at(?)=2.76 and 5.02 TeV is also predicted.Finally,the jet quenching effect of light nucleus O-O collision small system at(?)=7 TeV also was studied.We also assume that QGP is produced in O-O collisions,and known from the CLvisc(3+1)D hydrodynamic model that it has a similar initial temperature range to that of p-Pb collisions.Therefore,we use the same jet transport parameters as that of p-Pb collisions to predict the nuclear modifications of single inclusive hadron and ?-hadron in 7 TeV O-O collisions.Even if QGP matter is created in a small system,the jet quenching effect will be relatively weak due to the small size,so the cold nuclear matter(CNM)effect will be particularly important.Therefore,we first numerically simulate the CNM effect on both observables.The numerical results show that the single hadron productions have been increased by about 5%at large transverse momentum due to the CNM effect and the ?-hadron productions have been increased by 10-20%in the range of pT?=12-40 Gev/c and by 10%in the range of pT?=40-60 Gev/c.Taking the jet quenching effect into account,the yields of single hadron in central O-O collisions were suppressed by about 40-60%at pT?20 GeV/c,and the suppression decreases to 0-5%with the increasing of PT to 100 GeV/c.While the ?-hadron productions have a 10-20%suppression in the range pT?=12-40 GeV/c.