Phenomenological Constraints on the Transport Properties of QCD Matter with Data-Driven Model Averaging.

Using combined data from the Relativistic Heavy Ion and Large Hadron Colliders, we constrain the shear and bulk viscosities of quark-gluon plasma (QGP) at temperatures of ∼150-350 MeV. We use Bayesian inference to translate experimental and theoretical uncertainties into probabilistic constraints for the viscosities. With Bayesian model averaging we propagate an estimate of the model uncertainty generated by the transition from hydrodynamics to hadron transport in the plasma's final evolution stage, providing the most reliable phenomenological constraints to date on the QGP viscosities.

Azimuthal asymmetry of direct photons in high energy nuclear collisions.

We show that a sizable azimuthal asymmetry, characterized by a coefficient nu2, is to be expected for large pT direct photons produced in noncentral high energy nuclear collisions. This signal is generated by photons radiated by jets interacting with the surrounding hot plasma. The anisotropy is out of phase by an angle pi/2 with respect to that associated with the elliptic anisotropy of hadrons, leading to negative values of nu2. Such an asymmetry, if observed, could be a signature for the presence of a quark gluon plasma and would establish the importance of jet-plasma interactions as a source of electromagnetic radiation.

Correlated emission of hadrons from recombination of correlated partons.

We discuss different sources of hadron correlations in relativistic heavy ion collisions. We show that correlations among partons in a quasithermal medium can lead to the correlated emission of hadrons by quark recombination and argue that this mechanism offers a plausible explanation for the dihadron correlations in the few GeV/c momentum range observed in Au+Au collisions at the BNL Relativistic Heavy Ion Collider.

Hadronization in heavy-ion collisions: recombination and fragmentation of partons.

We argue that the emission of hadrons with transverse momentum up to about 5 GeV/c in central relativistic heavy ion collisions is dominated by recombination, rather than fragmentation of partons. This mechanism provides a natural explanation for the observed constant baryon-to-meson ratio of about one and the apparent lack of a nuclear suppression of the baryon yield in this momentum range. Fragmentation becomes dominant at higher transverse momentum, but the transition point is delayed by the energy loss of fast partons in dense matter.