Quantitative Study On Jet Quenching In Relativistic Heavy-Ion Collisions

Since the seventies of the 20th century when the quark-gluon plasma (QGP) had been predicted, ultra-relativistic heavy-ion collision is an effective experimental tool to explore the QGP matter at high energy and high density environment. QGP matter has been created at an early stage of the Big Bang, to study QGP will help to understand the universe evolution, formation of stars and microstructure of matter. In the experiments of ultra-relativistic heavy-ion collisions where QGP only exists for a very short time in the initial collisions, how to estimate the formation of the QGP and study its properties from the final created hadrons has been an extremely important research frontier in high-energy nuclear physics. Through the great efforts of many physicists, the experiments of high-energy heavy-ion collisions had been carried at the BNL Relativistic Heavy Ion Collider (RHIC) and the CERN Large Hadron Collider (LHC). A large number of experiment data prove that the QGP has been created, in which one important evidence for QGP formation is the jet quenching at large transverse momentum.In the early time of high-energy heavy-ion collisions energetic partons are induced to radiate and lose energy due to multiple scattering to QGP medium, so the final hadrons are greatly suppressed as compared to p+p collisions. This is so called as jet quenching. Jet quenching or suppression of final hadron spectra with large transverse momentum not only tests the predictions of pQCD, but also shows the time and space evolution of QGP, so jet quenching study in high-energy heavy-ion collisions has attracted intensive attentions from both theorists and experimentalists. From the run of RHIC to LHC, the energy of the heavy-ion collisions becomes higher and higher, more and more experimental data were gathered. The research of hard probe to QGP is getting into the era of quantitative study. In this paper, with next-to-leading order (NLO) perturbative QCD (pQCD) parton model, we utilize a (3+1) dimensional ideal hydrodynamic model to obtain the space-time evolution of the QGP and theoretical studies for jet energy loss in a high-twist approach, study the productions and suppression of single hadron and dihadron at large transverse momentum in different central nucleus-nucleus collisions at both RHIC and LHC, and calculate quantitatively the jet energy loss by extracting and analysing jet transport coefficient.Firstly, we quantitatively calculate and analyse the jet transport properties via large pT hadron production in central Au+Au collisions at RHIC and Pb+Pb collisions at LHC. Theory studies show that jet transport parameter and mean free path are two im-portant parameters of the jet transport properties. In this paper, with NLO order pQCD parton model, we utilize the jet transport parameter and mean free path to control jet energy loss which is imported into the effective medium-modified parton fragmentation functions. Consequently, we can simultaneously extract and analyse jet transport pa-rameter q and mean free path λ by calculating nuclear modification factor RAA for final large transverse momentum hadrons in most central nucleus-nucleus collision at at both RHIC and LHC. From simultaneous χ2/do.f. fits to experimental data, we extract values of jet transport parameter q0 and mean free path Ao at the center of the most central nucleus-nucleus collisions in the given initial time τ0.Our results for q0 are consistent with those by Jet Collaboration. Our numerical analysis of mean free path λ0 shows that the best fit falls between the single scattering limit and multiple scattering limit for the energetic jets propagating through QGP medium. This result academically give different judgment between the single scattering approximation and multiple scattering approxi-mation. Moreover, utilizing the jet transport parameter q0 and the mean free path λ0, we obtain the value of average transverse momentum broadening squared for the energetic jets propagating through the QGP, which implies that the jet may traverse through the medium with small reflection and justifies the eikonal approximation usually used in jet quenching calculations.Secondly, we quantitatively calculate and analyse the nuclear modification factors for single hadron and dihadron in different central Au+Au collisions at RHIC and Pb+Pb collisions at LHC. In the above work, jet transport parameter and mean free path are not independent observable, which is shown by our numerical results. We improve our model by introducing the average number of scattering gluons given by recent studies in high-twist approach. The average number of scattering including mean free path is associated with jet transport parameter. We study nuclear modification factor RAA for single hadron and IAA for back-to-back dihadron in different central nucleus-nucleus col-lisions at both RHIC and LHC. From simultaneous χ2/do.f. fits to experimental data, we extract values of initial jet transport parameter q0, which is consistent with our above work. It proves that the jet quenching description is consistent not only between single hadron and dihadron production, but also between central and oncentral nucleus-nucleus collision. Based on a (3+1) dimensional ideal hydrodynamic model for QGP space-time evolution, we get nuclear modification factor to fit data well for different centralities in nucleus-nucleus collisions, and prove different volume and life time of QGP produced in different centralities in nucleus-nucleus collisions. In the future, the nucleus-nucleus col-lisions experiment at more higher energy might run at CEPC-SPPC in China, we study in advance nuclear modification factors for final single hadron in different central nucleus-nucleus collisions at center-of-mass energy 30TeV and 100TeV, we give the reference values of nuclear modification factors.In the last, we study the medium temperature T dependence of jet transport param-eter and extract the value of jet transport parameter. In our previous works, we assume that jet transport parameter is proportional to the third power of QGP temperature, but recent researches show that there is extra temperature dependence of jet transport param-eter. We assume that （？）/T3 linearly depends on the temperature of QGP, and introduce two parameters:qc at critical temperature Tc= 170MeV and qn at maximum temperature Th{Th= 373MeV at RHIC). Applying the next-to-leading order (NLO) perturbative QCD (pQCD) parton model, we calculate nuclear modification factors RAA and elliptic flow v2 for final hadron in high-energy nucleus-nucleus collisions. Prom fitting to experimental data, we find that （？）/T3 has a peak at critical temperature Tc= 170MeV nearby. Con-trasting to the situation of a constant （？）/T3, the extra temperature dependence make a jet lose more energy near critical temperature, and enhances the anisotropy of jet energy loss. This will help to understand elliptic flow at large PT.Among all possibilities we pro-vide between （？）/T3 and QGP temperature, experimental data choose that （？）/T3 increases toward the critical temperature, which is a new perspective different from others.