Exploring Collectivity Effects In E-p Deep-inelastic Scattering And Photoproduction Processes With HERA H1

The search for a new state of matter,the quark-gluon plasma(QGP),has been the major component of the heavy-ion physics programme.There is strong evidence of its observation;one of the key observations being the collective behaviour of final-state particles.Collectivity,which is due to the initial spatial anisotropy transporting to particle momentum space anisotropy,can be characterized final-state particle correlations.These collective behaviours in heavy-ion collisions can be described within the framework of relativistic fluid dynamics,employing the thermodynamic and transport properties of quantum chromodynamics(QCD)matter.Recent measurements in proton-nucleus(pA)and proton-proton(pp)collisions at the Relativistic Heavy Ion Collider(RHIC)and the Large Hadron Collider(LHC),have revealed similar collective behaviour in smaller colliding systems at high multiplicity.It is unclear whether this collectivity observed also origins from hydrodynamic flow of,a strongly interacting and expanding medium.Comparing to pp and pA collisions,which typically have colliding region of the size of proton,e-p collisions at HERA usually probes smaller region which depends on 1/Q.Therefore,collectivity studies in positron-proton(e+p)collisions are expected to provide valuable information for the origin of collective behaviours.Whether there are strongly interacting medium in an even smaller colliding system is the question to be answered.These motivate our search for collectivity in ep collisions at HERA H1 experiment.The data used in this thesis were collected using H1 detector at HERA for deep inelastic scattering(DIS)and photoproduction processes in ep collisions at(?)GeV energy.It is the first-time collectivity measurement of photoproduction process in ep collisions,where two-particle azimuthal correlation method is used to search for collective signals,Since no long-range ridge structure is observed in correlation functions over the full multiplicity range,upper limits of ridge yield are provided as functions of particle multiplicity.The secondorder(V2?)and third-order(V3?)azimuthal anisotropy Fourier harmonics of charged particles are extracted from long-range two-particle correlations as functions of particle multiplicity.V2? and V3? values in DIS process are apparently larger than those in pp collisions.These results are well-described by Monte Carlo simulations without collectivity,indicating small room for the existence of collectivity in ep collisions.V2? and V3? values in photoproduction process have a similar trend comparing to those in DIS.The decreasing trend of V2? as function of multiplicity,as well as the negative V3? values,suggesting small,if not zero,contribution from collective flow.These results shed light on the origin of collectivity in small systems and provide guidance to future collectivity researches in high luminosity ep and eA collisions at EIC.