12-18 August 2012
US/Eastern timezone

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Influence of initial state fluctuations on the production of thermal photons

17 Aug 2012, 15:40
20m
Empire ()

Empire

Oral Presentation Electroweak probes Parallel 6E: Initial State and p-A (Chair E. Wang)

Speaker

Dr Rupa Chatterjee (University of Jyväskylä)

Description

Thermal emission of photons from relativistic heavy ion collisions is believed to have a very strong temperature dependence and the high p_T thermal photons are expected to provide a glimpse of the early part of the expansion history when the system is still in the plasma phase. Photons having p_T > 1 GeV/c are thus specially suitable for probing fluctuations in the initial QCD matter density distributions. We present the p_T spectra, ratio of central to-peripheral yield and elliptic flow of thermal photons from an event-by-event ideal hydrodynamic calculation with fluctuating initial conditions (IC). We show that fluctuations in the IC enhance the production of thermal photons significantly in the range 2 < p_T < 4 GeV/c compared to a smooth initial-state-averaged profile for Au+Au (Pb+Pb) collisions at RHIC (LHC) [1,2]. The relative effect of fluctuations in the IC is found to be stronger for peripheral collisions and for lower beam energies. Thermal photon p_T spectra are studied for different values of initial formation time \tau_0 as well as for centrality dependent \tau_0 values. We show that a suitably normalized ratio of central-to-peripheral yield as a function of collision centrality and p_T can be a useful measure of the fluctuation size scale [2]. PHENIX data for direct photon elliptic flow at RHIC is found to be significantly larger than the v_2 results obtained using ideal hydrodynamics with smooth IC in the region 1 < p_T < 6 GeV/c. We show that fluctuations in the IC increase the elliptic flow for p_T > 2 GeV/c for mid-central collisions compared to the results from a smooth initial-state-averaged profile [3]. We also show that these results depend strongly on the value of the fluctuation size scale as well as on the initial and final conditions of the hydrodynamic calculation [3]. [1] R. Chatterjee, H. Holopainen, T. Renk, and K. J. Eskola, Phys. Rev. C 83, 054908 (2011); R. Chatterjee, H. Holopainen, T. Renk, and K. J. Eskola, J. Phys. G 38, 124136 (2011). [2] R. Chatterjee, H. Holopainen, T. Renk, and K. J. Eskola, arXiv:1204.2249 [nucl-th]. [3] R. Chatterjee, H. Holopainen, T. Renk, and K. J. Eskola [in preparation].

Primary author

Dr Rupa Chatterjee (University of Jyväskylä)

Co-authors

Dr Hannu Holopainen (Frankfurt Institute for Advanced Studies) Prof. Kari J. Eskola (University of Jyvaskyla) Dr Thorsten Renk (University of Jyväskylä)

Presentation Materials

Paper

Paper files: