Multiplicity Dependent Charged Particle Jet Production In Pp Collision At S^1/2=13 TeV

Quarks and gluons are the elementary particles and the interactions between them can be described by Quantum ChromoDynamics(QCD).QCD theory believes that quarks and gluons are confined in the nucleus.It is impossible to extract free quarks and gluons in the nuclear matter.Lattice Quantum ChromoDynamics(LQCD)predicts that under extreme high temperature or high density conditions,quarks and gluons will be deconfined from the nuclear matter and become free and isolated,forming the Quark-Gluon-Plasma(QGP).Studying the QGP formation and its properties can help us to understand the evolution of the universe,the creation of the matter and the changes of various neutral stars.Therefore,the search of QGP properties has become one of the important topics in the field of high-energy nuclear physics.Particles are accelerated and then collided at the Relativistic Heavy Ion Collider(RHIC)or the Large Hadron Collider(LHC)under laboratory conditions.Their interactions will generate the hot QGP medium,which allows us to study the QGP properties in laboratory.The LHC is the largest particle accelerator in the world,located at the European Organization for Nuclear Research(CERN).The ALICE is one of the main experiments at the LHC,with the main purpose to study the QGP properties created in the heavy-ion collisions.Due to the existences of QGP time is very short,we can only study the QGP properties by measuring the final-state particles activities in the collisions.Hard scattering involves the large energy transfer from the nucleus-nucleus colli-sions,which usually produces a back-to-back parton pair,the hard scattered partons will eventually hadronized into final state particles after partonic shower.Jet,is the spray of hadrons from high momentum hard scattered partons fragmentation which collimated in the finite space.It will lose energy when traversing the hot QGP medi-um,such process is called jet-quenching effect.Therefore,jet-quenching is considered to be a powerful probe to study QGP in the heavy-ion collisions.Jet-quenching will not only lead to the suppression of the high pT jet production,but also change the hadronic constituent inside the jet.So fax,a large number of experimental observables have been studied to probe the QGP properties.QGP medium is expected to be created in the heavy-ion colli-sions,however,by studying the QGP observables in high multiplicity proton-proton collisions we have observed similar behavior as shown in heavy-ion collisions where QGP presents.Whether the QGP is formed in small system with high multiplicity environment is still an open question,which is requires further investigation.To that end,the motivation for this thesis is t.o study jet production in different multiplicity proton-proton collisions in order to explore the QGP existences in small system.Using the LHC-RUN-II large data taking,by ALICE detector,I have analyzed the jet production yield in proton-proton collisions at ?s = 13 TeV,and obtained the charged jet cross sections in different multiplicity intervals.I have also studied the jet cross sections using different jet resolution parameters to understand the jet collimation behaviour.In conclusion,we found that more jets are produced in high multiplicity intervals compared to the inclusive one,while the jet production en?hancement in high multiplicity environments has week jet pT or resolution parameter dependences.As expected,I also confirmed the jets get more collimated at high pT in different multiplicity intervals,with no collision energy or multiplicity dependence when compared to earlier publication results.