Study Of Jet Properties Under High Multiplicity Environment In Heavy-ion Collisions

The study of properties of the new quark matter,Quark-Glue Plasma(QGP).at extreme high temperature and high energy density is one of the leading topics in modern physics.It will further reveal the nature of strong interacting derived phase transitions and strongly-interacting substances,and further expand people's understanding of the basic physical laws of the nature;at the same time,it will provide an important reference for understanding the early evolution history of the universe,the internal structure of neutron stars and the current cosmological observations.High energy particle jets formed by hard parton fragmentation in the final state of high-energy heavy ion collision is an extremely effective probe to determine the QGP signal and to investigate properties of the QGP.The interaction between initial hard partons and the QGP medium will not only induce large-angle gluon radiation,resulting in energy loss in the jet cone;but will also affect the gluon radiation spectrum in the jet cone,leading to the change of the internal structure of the jet.For the above two effects,the former can be quantified by measuring the inclusive jet spectrum and the latter needs to be studied in depth by accurate measurement of the modified jet components.When the jet is reconstructed in Pb-Pb collisions,a large number of soft particles with low transverse momentum give the background in jet reconstruction.Background and it's fluctuations affect the measurement of the jet spectrum.By the studying of background fluctuations,the effect of background fluctuations on the jet spectrum measurement can be corrected by using the unfolding method.However,this correction also increases the uncertainty on the measurement.By analyzing the jet constituents,the reconstructed sub-jet is proposed to overcome the influence of the uncorrelated background on the jet structure,and to be more sensitive to different transport mechanisms of the hard parton in the hot dense medium with the inclusive jets.In the Thesis ALICE environment will be introduced firstly.Then,the subtraction of jet background and the correction for into fluctuation effect on the jet production are studied in the Pb-Pb collisions.Furthermore,the performant study of the jet components in heavy ion collisions is presented via a "ToyMC" simulation.Finally,a new observable based on the sub-jet structure that can effectively overcome the effects of background fluctuations is investigated in Pb-Pb collisions at 5.02 TeV with ALICE.All studies presented in the thesis will provide important insight into understanding the transport mechanisms of hard probes in the QGP medium at high energies and high luminosities...