Heidelberg 2015 – scientific programme
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HK: Fachverband Physik der Hadronen und Kerne
HK 64: Heavy Ion Collisions and QCD Phases 8
HK 64.1: Group Report
Thursday, March 26, 2015, 17:00–17:30, T/HS1
Understanding photon production in hadron collisions and the equilibrating QGP in the early stage of the heavy-ion collisions — •Olena Linnyk1, Elena Bratkovskaya2, and Wolfgang Cassing1 — 1Justus Liebig University of Giessen, Germany — 2Goethe University Frankfurt am Main, Germany
We show that the differential spectra, elliptic flow v2, triangular flow v3 and the polarization of emitted real and virtual photons reflect the properties of the QCD matter under extreme conditions as created in relativistic heavy-ion collisions: its temperature, sheer viscosity, conductivity and degree of equilibration. The first several fm/c of the collision evolution are particularly interesting, because the properties of the system before it equilibrates to QGP or hadron matter are not yet established. On the other hand, photons are emitted by every moving charge, a multitude of sources has to be disentangled in order to access the signal of interest. The direct photons at low transverse momentum are dominated by the thermal radiation from the QGP and the secondary meson+meson and meson+baryon interactions, such as the two-to-two processes (pi+pi->rho+gamma, rho+n->n+gamma, etc) and the bremsstrahlung mechanism (h+h->h+h+gamma). The implementation of photon bremsstrahlung in transport approaches was based until now on the soft photon approximation (SPA); it is valid only at very low energy (and pT) of the produced photon. Presently, we go beyond the SPA and use a one-boson-exchange model. Understanding the conventional sources lets us access the novel mechanisms of photon radiation in the non-equilibrium QCD matter and Glasma