Recent Results from the RHIC Experiments Searching for QGP

Abstract

The relativistic heavy ion collider (RHIC) at Brookhaven National Laboratory (BNL) have provided Au+Au, d+Au and p+p collisions at s N N = 200 GeV. The prime purpose of the heavy ion collisions is to produce and to study the property of a new state of matter: Quark Gluon Plasma (QGP) at an extreme conditions; high temperature and density. The several experiments (STAR, PHENIX, BRAHMS and PHOBOS) at RHIC are trying to find signals of the QGP. Small collision systems (d+Au and p+p) were also examined to establish the bases for the comparison with the heavy ion collisions with Au+Au. The jet suppression at high p T found in Au+Au collision was an unique feature of the heavy ion collisions, where jets were even slightly enhanced in the light system with d+Au collisions. This might be explained by the energy loss of high energy partons traveling through the QGP matter. Another striking evidence found in the heavy ion collisions was the quark number scaling of the elliptic flow parameter: v 2 , which might reflect the existence of the QGP phase in the earlier time when v 2 is generated. The chemical and thermal freeze-out parameters give the later history of the collision, having in mind that the trend of the chemical freeze-out temperature is approaching to the expected phase boundary as a function of the beam energy, the system might have already been in the QGP phase in earlier time before the hadronization.