In heavy ion collisions at relativistic energies conducted at Relativistic Heavy Ion Collider (RHIC, Upton, USA) a new state of matter, Quark Gluon Plasma (QGP), is produced. QGP is a state of matter with partonic (i.e. gluons + quarks) degrees of freedom and is believed to be existing only during first moments after the Big Bang, and possibly inside of the heaviest neutron stars. One of the key QGP signatures is the elliptic flow (v2) - a coefficient that describes spatial assymetry of particle yield. It has been observed that v2 of particles composed of light quarks (i.e. up, down and strange) follow the same trends when scaled to the number of constituent quarks. Such observations implied that all light quarks gain the same flow in the heavy ion collision. On the other hand it was speculated that heavy quarks (charm and bottom) should have smaller v2 because of their in-medium energy losses. Due to their heavy mass, c quarks are produced mostly before QGP is formed, which makes them excellent probes to study this hot, dense and strongly interacting medium. The Solenoidal Tracker At RHIC (STAR) experiment took data with the newly installed Heavy Flavor Tracker (HFT) detector. Thanks to the state-of-the-art tracking resolution of the HFT it is possible to measure D0 mesons with unprecedented precision. This paper presents the STAR experiment measurement of D0 elliptic flow.
It is believed, that shortly after the Big Bang the Universe existed in the state of the Quark Gluon Plasma, where quarks and gluons act as quasi-free particles. During relativistic heavy ion collisions this state of matter can be reproduced. Quantum Chromo-Dynamics (QCD) calculations show possible existence of the critical point and the 1st order phase transition between hadron gas and QGP. The Relativistic Heavy Ion Collider’s (RHIC) program called Beam Energy Scan (BES) was developed for experimental verification of above QCD predictions. Within this program the Solenoidal Tracker At RHIC (STAR) experiment gathered data from gold-gold collisions at √sNN = 7.7, 11.5, 14.5, 19.6, 27, 39, 62.4 and 200 GeV. This data are analysed by STAR Collaboration in search for answers to questions concerning the nuclear matter phases, namely: what is the collision energy for the onset of the QGP formation? What is the nature of a phase transition between QGP and hadron gas? Is there a critical point and if yes, where is it situated? In this proceedings a few of the latest STAR results that address these questions are presented.
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