Probing QCD Phase Transition From The Strange Hadron Production In Relativistic Heavy-ion Collisions

The Quark-Gluon Plasma(QGP),which is a kind of matter under extreme high temperature and high density,is created in the collision of two high energy heavy-ion beams in relativistic heavy-ion collision experiments.Along with the reduction of temperature,the QGP will transform to the hadronic matter and the transition is called QCD phase transition.The main physical goal of heavy-ion collision experiments is to study the properties of QCD phase transition.Because the mass of strange quark has the same magnitude as the QCD phase transition temperature,strange quarks can be abundantly produced in QGP.The production of strange hadrons which contains starnge quarks is considered a idea observation to address the QCD phase transition.In this paper,we study the properties of QCD phase transition via the production of strange hadrons in heavy-ion collisions.We argue that yield ratio of strange hadrons OK-?-?-A=N(K+)N(?-)/N(?)N(A)is sensitive to strange quark density fluctuation.Based on the quark coalescence model which can take into account the effect of quark density fluctuations,we prove that the yield ratio OK-?-?-A correlates with strange quark density fluctuation directly.By analyzing the data from experiments,a possible non-monotonic behavior in the ratio as a function of collision energies can be seen.This is in contrast to the coalescence model without quark density fluctuations and also to the statistical model.The yield ratio OK-?-?-A shows the non-monotonic behavior of strange quark density fluctuation and it can be used to study the physical fluctuations caused by QCD phase transition.Then we apply this coalescence model with density fluctuations in the hypernuclei system.For the S3 factor which changes obviously with collision energies found in the heavy-ion collision experiments,we suggest that the difference between theortical calculations and experiment results mainly due to the different feed-down corrections for proton yield.We also suggest that the yield ratio of hypertriton,? and deuteron S2=N3?H/N?Nd can be a promising observation to study the baryon-strangeness correlation in heavy-ion collisions.Based on the calculation in the framework of coalescence model,we extract the correlation coefficient aAd between A and deuteron density fluctuations from the value of S2 from experiments.And it shows a strong dependence on the collision energy.The ratio S2 which shows the behavior of baryon-strangeness correlation in heavy-ion collisions can be a new observation for studying the QCD phase transition in experiments.A multiphase transport(AMPT)model fails to describe the production of strange baryons in heavy-ion collisions.We introduce additional coalescence factors for strange baryons in AMPT model and the model can describe the enhanced production of strange baryons observed in Au+Au collisions at(?)=200GeV and in Pb+Pb collisions at(?)=2.76TeV after being extended.It can also give a reasonable description of the multiplicity dependence of strangeness enhancement observed in small system collisions.Our work provides a convenient way to model the mechanism of strangeness enhancement in heavy-ion collisions.Our work indicates that the strange quark dynamics is an effective probe to study the nature of QCD phase transition and to locate the boundary of QCD phase transition.The results in this paper provides new research methods and ideals for the future heavy-ion collision experiments for example the BES-II program at STAR.