Location: Cyclotron Building (434), Seminar Room
One of the most important issues that arises in the study of relativistic heavy-ion collisions is that of the creation of a new state of matter, quark-gluon-plasma (QGP). Since the plasma life time and volume are small, various 'probes' of QGP detection have been proposed, such as jet-quenching, photon and dilepton production e.t.c. In this talk the prospect of photons as a possible probe is being discussed.
The dihadron azimuthal correlations triggered by energetic particles in heavy ion collisions at RHIC are studied in a multiphase transport (AMPT) model. A double-peak structure at the away side of triggered particles is obtained after subtracting background correlations due to the elliptic flow as observed in experiments. Both the near-side peak and the away-side double peaks are, however, significantly reduced (enhanced) in events with small (large) triangular flow, which are present as a result of fluctuations in the initial collision geometry. After the subtraction of background correlations due to the triangular flow, the away-side double peaks change into a single peak with broad shoulders. Further subtraction of higher-order flows leads to essentially a single peak at the away side of triggered particles. Implications of these result on the jet-medium interactions in relativistic heavy ion collisions will be discussed.
In this talk I will review our theoretical understanding of the dynamics of a non-equilibrium quark gluon plasma. I will begin by discussing the emergence of strong local momentum-space anisotropies in the plasma due to the rapid longitudinal expansion of the plasma at early times. While strongly-coupled plasmas might remain approximately isotropic in the center of the collision region at late times, weakly-coupled plasmas do not, and even strongly-coupled plasmas generate large momentum-space anisotropies near the transverse and longitudinal edges of the plasma. I will explain why second order viscous hydrodynamics should not be trusted to describe such highly anisotropic plasmas and present a framework to derive hydro-like equations that can better describe highly anisotropic systems. I will present results of the application of this framework to two specific cases: boost-invariant and non-boost-invariant evolution of the quark gluon plasma. If time permits, I will close by discussing the implications for the collective modes of an anisotropic plasma and present recent numerical simulations of Yang-Mills coupled to hard particles in a dynamically expanding background.
For polarized protons colliding at RHIC energies, the production of jets and hadrons is dominated by gg and qg scattering, making the double longitudinal spin asymmetry, A_LL, sensitive to gluon polarization in the nucleon. I will present STAR results of A_LL from inclusive and correlated probes for the RHIC 2006 run totaling 4.7 pb^-1 of integrated luminosity with 60% average beam polarization at center-of-mass energy 200 GeV. I will also present recent high-precision results on jets and dijets from the 2009 run, which collected a much larger sample with 20 pb^-1 and 58% average beam polarization, also at center-of-mass energy 200 GeV. The results are compared with theoretical calculations of A_LL based on various models of the gluon density in the nucleon. The STAR data place significant constraints on allowed theoretical models.
For polarized protons colliding at RHIC energies, the production of jets and hadrons is dominated by gg and qg scattering, making the double longitudinal spin asymmetry, A_LL, sensitive to gluon polarization in the nucleon. I will present STAR results of A_LL from inclusive and correlated probes for the RHIC 2006 run totaling 4.7 pb^-1 of integrated luminosity with 60% average beam polarization at center-of-mass energy 200 GeV. I will also present recent high-precision results on jets and dijets from the 2009 run, which collected a much larger sample with 20 pb^-1 and 58% average beam polarization, also at center-of-mass energy 200 GeV. The results are compared with theoretical calculations of A_LL based on various models of the gluon density in the nucleon. The STAR data place significant constraints on allowed theoretical models.