The fixed-target experiment at STAR

Abstract

The RHIC Beam Energy Scan (BES-I) program, which covers center-of-mass energies 7.7 GeV to 39 GeV, was proposed to look for the turn-off of signatures of the quark gluon plasma, search for a possible QCD critical point, and study the nature of the phase transition between hadronic and partonic matter. RHIC BES-I has shown that the partonic interactions are dominant at center-of-mass energies above 20 GeV. Several observables, including v1 of protons and Lambdas, v2 of all identified hadrons, and net-proton higher moments, show interesting behavior below 20 GeV and could suggest a transition to a hadron interaction dominated regime. Data from energies lower than 7 GeV could help determine whether these behaviors are indicative of phase transitions or criticality. The goal of the STAR Fixed-Target Program is to extend the collision energy range in BES II to lower energies than what is feasible at RHIC with colliding beams. First physics results from test runs of Au + Au fixed-target collisions will be presented. The results will be compared with published results from similar collision energies at the AGS. The implications for the fixed-target program after the completion of the inner TPC (iTPC) and endcap TOF (eTOF) detector upgrades will also be discussed.