Studies Of Electroweak Boson Tagged Jets In Heavy Ion Collisions

A new form of matter——quark gluon plasma is created in relativistic heavy ion collisions both at RHIC and the LHC.Investigations about the properties of this hot and dense QCD medium is a hot point for both theorists and experimentalists.Due to the short lifetime one could not observe QGP directly at present.Therefore a series of probes were developed.High transverse momentum partons produced at the early stage of these collisions will lose energy via interactions with medium partons when they transverse through QGP.This phenomenon is called jet quenching and regarded as one of most powerful probes.It can lead to not only the suppression of leading hadron production,but also the modification of full jet observables.As the development of jet reconstruction technique and theoretical model,full jet observables have draw increasing attentions.Electroweak bosons tagged jet has long been regarded as the“golden channel”,since bosons will not interact with medium partons and will not lose energy in QGP,it could carry the initial energy information of partons which is tagged by the boson.In this thesis we focus on W tagged jets.We first calculate the production of W+jets in p+p collisions by using Sherpa event generator at Leading Order(NL)and Next to Leading Order(NLO)matched with parton shower(PS),and compared them with ATLAS data.We found NLO+PS could provide more reasonable description of experimental data.Base on good baseline given by Sherpa(NLO+PS),the well established Linear Boltzmann Transportation Model is used to calculate parton energy loss in Pb+Pb collisions.We present four observables in W+jets events in Pb+Pb collisions in this thesis:·Rjw:the number of jets tagged by W.We studied Rjw as a function of pTW.And we found that the Rjw of W+all jets is suppressed in the overall ??jw region and the contribution of sub-jets is very small in overall ??jw region.So we conclude that the lower production of sub-jets is the reason of no strong suppression in high pTW region.·Xjw:the transverse momentum imbalance between W and any one of jets.We studied distributions of xjw in p+p and Pb+Pb collisions for W+all jets and W+sub-jets.And we found xjw is broadened and shifted toward a smaller xjw value in Pb+Pb collisions compared with that in p+p counterpart.And in high pTW region,the contributions of multi-jets is more important and the broadening effect is more visible.·<xjw>:the averaged xjw.We studied(xjw)as functions of pTW for W+all jets and W+ leading jet.And we found that the<xjw>of W+ leading jet is larger than W+all jets and this discrepancy is more obvious as the increasing of pTW.Because a leading jet or single jet has larger transverse momentum than any one of all jets.·??jW:the azimuth angle correlation between W and any of jets.We compare the distributions of ??jW for W+all jets,W+leading jet and W+sub-jets both in p+p and Pb+ Pb collisions.And we found that the ??jW distribution of W+all jets is slightly suppressed in the overall ??jw region,this nuclear modification is due to the domination of W+ leading jet in large ??jW region and W+sub-jets in small ??jW region and they both are slightly suppressed in these region.