Results from beam energy scan program at RHIC-STAR

Abstract

Nuclear matter at extremely high temperature and high density is expected to undergo a phase transition to a different state of matter, that is made of deconfined quarks and gluons, such as Quark Gluon Plasma (QGP). The QGP is believed to have existed in early universe just after the Big Bang and/or inside neutron stars. High energy heavy-ion collisions have been carried out in various experiments at AGS, SPS, RHIC and LHC accelerator facilities at Brookhaven National Laboratory (BNL) and European Organization for Nuclear Research (CERN) to create and explore such new state of matter. The experimental results at the highest possible energy regions at RHIC and LHC indicate that the new state of matter has indeed been formed with a partonic degree of freedom, and the phase transition seems to be a smooth crossover that is also expected from the theoretical calculations in the high temperature region of the Quantum Chromo Dynamics (QCD) phase diagram. In the high density area of the QCD phase diagram, the transition is expected to be a first order phase transition and there could be a critical end point for the first order phase transition. The high density region can be reached by lowering the beam energy to a few GeV to a few 10 GeV. Experimental studies with heavy-ion collisions aiming at this high density region are currently being pursued at SPS and RHIC. Future facilities at FAIR, NICA, HIAF and J-PARC are planned. The STAR experiment has been extensively working on the beam energy scan program at RHIC especially around this beam energy region in order to find the first order phase transition as well as signatures from the critical end point in the QCD phase diagram. The recent experimental results of STAR collaboration from the RHIC beam energy scan program will be presented and discussed in this proceedings.