A Model Study On The Multiplicity-dependent Strangeness Enhancement In Pp Collisions

Quantum chromodynamics(QCD)predicts that the partonic degree of freedom in nuclear matter will be released in high temperature and high density environment,forming a new form of matter called Quark-Gluon Plasma(QGP).The high tem-perature and high density environment is created by high energy heavy ion collisions in the experiment(such as the Large Hadron Collider on Pb-Pb collisions)to form QGP.Strangeness enhancement has been considered as a very important signature for the formation of QGP matter.In the case of the QGP,the strange quark will reach the thermal equilibrium with other light quarks.The relative yield of strange quark is larger than that of common nucleon matter system,so the relative yield of strange particles will also increase.The increase of relative yield is more obvious on the strange particles with larger strange number.Interestingly,a significant multiplicity dependent strangeness enhancement for small scale collision systems(pp and p-Pb collisions)is observed in the recent ALICE experiment at the LHC.This discovery has attracted wide attention from the academic community.However,there is still no theory to explain the experimental phenomenon well until now.Based on the research status in the related fields,the thesis applies the PYTHIA model and the PACIAE model to explore the possible reason of the strangeness en-hancement in pp collisions.The research considers mainly the influence of the color reconnection effect in the PYTHIA model.The results show that the color reconnec-tion mechanism can bring more obvious strangeness enhancement by adjusting the related parameters of the probability of the strange quark production.In particular,the multiplicity dependence of Ω particle yield is much better than that without color reconnection effect.In addition,the effect of final state partons in pp collisions and the hadronic rescattering effect are considered in PACIAE model.The initial par-ton density of small collision system is too small and the contribution of final state interaction to the relative particle yield is not obvious,so it is unlikely to cause the strangeness enhancement in small systems.In summary,this research work studied the improved string fragmentation mech-anism and final parton,hadron interaction effect on the strange particles produced in proton-proton collisions,and discussed the possible factors of strangeness enhance-ment of small systems.It has an important significance for the understanding of char-acteristics of small collision system.