Jonah E. Bernhard, Peter W. Marcy, Christopher E. Coleman-Smith, Snehalata Huzurbazar, Robert L. Wolpert, Steffen A. Bass, arXiv:1502.00339 [nucl-th]

Abstract: We systematically compare an event-by-event heavy-ion collision model to data from the Large Hadron Collider. Using a general Bayesian method, we probe multiple model parameters including fundamental quark-gluon plasma properties such as the specific shear viscosity η/s, calibrate the model to optimally reproduce experimental data, and extract quantitative constraints for all parameters simultaneously. The method is universal and easily extensible to other data and collision models.

C. Shen, Z. Qiu, H. Song, J. Bernhard, S. Bass and U. Heinz, arXiv:1409.8164 [nucl-th]

Abstract: The iEBE-VISHNU code package performs event-by-event simulations for relativistic heavy-ion collisions using viscous hydrodynamics (+ hadronic cascade model). We present the detailed model implementations accompanied with some numerical code tests for this package. The iEBE-VISHNU builds up a general theoretical framework for model-data comparisons through large scale Monte-Carlo simulations. The numerical interface between hydrodynamical evolving medium and thermal photon radiation is also discussed. This interface is designed for generic calculations of all kinds of rare probes, which are coupled to the temperature and flow velocity evolution of the bulk medium, such as jet energy loss and heavy quark diffusion.

C. Shen, J. F. Paquet, J. Liu, G. Denicol, U. Heinz and C. Gale,  arXiv:1407.8533 [nucl-th]

Abstract: We consider directly emitted and hadronic decay photons from event-by-event hydrodynamic simulations. We compute the direct photon anisotropic flow coefficients and compare with recent experimental measurements. We find that it is crucial to include the photon multiplicity as a weighting factor in the definition of v^γ_n. We also investigate the sensitivity of the direct photon spectrum and elliptic flow to the theoretical uncertainty of the photon emission rate in the quark-hadron transition region and to the pre-equilibrium dynamics of relativistic heavy-ion collisions.

U. W. Heinz, J. Liu and C. Shen, arXiv:1403.8101 [nucl-th]

Abstract: Measurements of thermal photons emitted from the rapidly expanding hot and dense medium (“Little Bang”) formed in ultra relativistic heavy-ion collisions, and their current theoretical interpretation, are reviewed.

C. Shen, U. Heinz, J. F. Paquet and C. Gale, arXiv:1403.7558 [nucl-th]

Abstract: Photons are a penetrating probe of the hot and dense medium created in heavy-ion collisions. We present state-of-the-art calculations of viscous photon emission from nuclear collisions at RHIC and LHC. Thermal photons anisotropic flow coefficients v_n are computed, both with and without accounting for viscous corrections to the standard thermal emission rates. These corrections are found to have a larger effect on the v_n coefficients than the viscous suppression of hydrodynamic flow anisotropies. For thermal photons, the ratio v_2{SP}/v_3{SP} shows stronger sensitivity to the quark-gluon plasma (QGP) shear viscosity than for hadrons, and it can thus serve as a sensitive QGP viscometer.

C. Shen, U. W. Heinz, J. F. Paquet, I. Kozlov and C. Gale, arXiv:1308.2111 [nucl-th].

Abstract: We present state-of-the-art calculations of viscous photon emission from nuclear collisions at RHIC and LHC. Fluctuating initial density profiles are evolved with event-by-event viscous hydrodynamics. Momentum spectra of thermal photons radiated by these explosively expanding fireballs and their p_T-differential anisotropic flow coefficients v_n(p_T) are computed, both with and without accounting for viscous corrections to the standard thermal emission rates. Viscous corrections to the rates are found to have a larger effect on the v_n coefficients than the viscous suppression of hydrodynamic flow anisotropies. Since photons are found to be more sensitive to the quark-gluon plasma (QGP) shear viscosity than hadrons, their anisotropic flow coefficients v_n serve as a sensitive QGP viscometer.