Study Of Direct Photon With Statistical Methods In Pp Collisions At S^1/2=13 TeV With ALICE Detector

With the development of science and technology,people's exploration of the universe is also deepening.In the 1970s,scientists predicted that after the rela-tivistic high-energy heavy ion collision,there is an extremely high-temperature and high-density environment formed in a certain spatial region.Quarks and gluons con-finemented in hadrons would form a new material form after deconfinement-Quark gluon plasma(QGP).In the well-known theory of the Big Bang,it is generally be-lieved that the universe began in a high-temperature and high-density initial state about 1010 years ago,and then continued to expand until now.Based on this,we predict that QGP is a material form that exists in the initial period of the Big Bang,so studying QGP is of great significance for exploring the evolution of space and time.The QGP space-time scale is small,and the nature of the heat-tight medium in the initial stage of the collision can only be inferred by measuring the final physical observation measured by the collision.After years of research,people have proposed some physical observations,in which the photon with large transverse momentum is considered to be the ideal probe for studying the QGP state of matter,because photons do not participate in strong interaction,and the electromagnetic coincidence constant(?e=1/137)is very small,as well as photon can be detected away from the collision area,and carries original information of QGP.At present,the relativistic heavy ion collision experiment is one of the important methods to study quantum chromodynamics(QCD)and explore the related prop-erties of QGP,represented by the Large Hadron Collider(LHC)of the European Nuclear Research Center(CERN)and the Relativistic Heavy Ion Collider(RHIC)of the Brookhaven National Laboratory(BNL),This paper is based on the LHC-ALICE experiment,using statistical methods to study the production of direct photons in high-energy proton-proton collisions.The neutral ? meson is the largest background for direct photons,which are reconstructed by invariant mass method and single clus-ter analysis,respectively.For the final measurement,the results are combined in the overlapping pT inter.val of both methods.Direct photon spectra are extracted using the direct photon excess ratio R?,which quantifies the ratio of inclusive photons over decay photons generated with a decay-photon simulation.The benefit of using R? instead of trying to directly quantify the difference between photons and decay photons is that several system uncertainty is partially or completely eliminated.