Study of High Density Nuclear Matter Using Fixed Target Collisions at RHIC

• Terence John Tarnowsky (Purdue University (US))

There is still a great deal of uncertainty about the state of nuclear formed in low/intermediate energy heavy-ion collisions and described by Quantum Chromodynamics (QCD). Large value of net-baryon densities at these energies leads to substantial theoretical uncertainties. Some predictions indicate that at center-of-mass (CMS) collision energies below 5 GeV a mixed partonic/hadronic system is created. Before reaching an equilibrated QGP phase at higher energies, the system formed in heavy ion collisions at low/intermediate energies may pass through this mixed phase of partonic and hadronic matter, which has not been well quantified. In this regime, it is possible to observe the phase transition from hadronic matter to a deconfined partonic phase. Brand new physics opportunities at STAR/RHIC have recently opened up. With the installation of a gold foil target, STAR can operate in a fixed target mode with the unique capability to probe the nature of the QCD phase diagram below the maximum net-baryon density at hadronic freeze-out (maximum compression). This new capability of the STAR detector and the RHIC complex opens up a wide-range of possible physics programs. It is possible to study the onset of this deconfinement phase transition from hadronic to partonic matter at RHIC and if the phase transition is first order, as predicted by theory and hinted at by experimental studies. I will discuss first results from measurements of dynamical net-charge fluctuations in Au + Au and Al + Au collisions at CMS collision energies between 3 - 200 GeV from collider and fixed target operations, along with a proposal for a comprehensive study of this region of the QCD phase diagram by utilizing the new capabilities at RHIC.