Experimental Studies Of Strange Hadron Production In Heavy-ion Collisions At STAR/RHIC

Ultra-relativistic heavy-ion collisions are the most promising tool for the creation of a new state of matter with de-confined quarks and gluons as the basic constituents,referred as the Quark-Gluon Plasma(QGP).Strange particle production provides one of the most powerful tools to study the dynamics of the reaction.We systematically studied mid-rapidity(|y|<0.5)productions of KS0,? and ? in Au+Au collisions at(?)=14.5 GeV from the Relativistic Heavy Ion Collider(RHIC)Beam Energy Scan(BES-I),and measured the corresponding nuclear modification factors(RCP).By combining the measurements at different energies from the STAR experiment,we observed that the partonic energy loss effect becomes less significant when colliding energy is decreased,and the cold nuclear matter effect(Cronnin effect)starts to take over at(?)?14.5 GeV.Less baryon enhancement has also been observed in the ?/KS0 ratio at this energy,which suggest that there could be a possible change of underlying mechanism of the hadron formation and/or parton dynamics between 14.5 and 19.6 GeV.We studied the KS0 and ? production from the first Au+Au fixed-target collisions at(?)=4.5 GeV,and measured the transverse mass(mT)spectra and rapidity density distributions(dN/dy)from the top 5%central collisions.They were found to be consistent with different AGS experiments at similar energies.These results and those on charged hadrons demonstrate that the STAR can work in the fixed-target mode together with the collider mode.We then studied KS0 and ? production,the transverse mass(mT)spectra and rapidity density distributions from Al+Au fixed-target collisions at(?)=4.9 GeV.The observed yields of these two hadrons are consistent with previous published AGS results at sim-ilar energies.The ? rapidity density(dN/dy)was first measured at low rapidity and found to be consistent with the previous measurements at higher rapidity.The baryon stopping magnitude(?y=ypeak-ytarget)was observed to be 1.071±0.023±0.032 and is consistent with AGS experiments.The dN/dy measurements in different centralities also indicate that,the strange hadrons in these collisions originate dominantly from the hadronic association production processes.