Electromagnetic Radiation from Broken Symmetries in Relativistic Nuclear Collisions

Direct photons play an important role as electromagnetic probes from the quark-gluon plasma (QGP) which occurs during ultrarelativistic heavy-ion collisions. In this context, it is of particular interest how the finite lifetime of the QGP affects the resulting photon production. Earlier investigations on this question were accompanied by a divergent contribution from the vacuum polarization and by the remaining contributions not being integrable in the ultraviolet (UV) domain...

We compare the photon emission rates from hot hadronic matter with in-medium mass shift and Quark Gluon Plasma (QGP). It is observed that the WA98 data can be well reproduced by hadronic initial state with initial temperature $\sim 200$ MeV if the universal scaling of temperature dependent hadronic masses are assumed and the evolution of temperature with time is taken from transport model or (3+1) dimensional hydrodynamics. The data can also be reproduced by QGP initial state...

The production of single photons in relativistic heavy ion collisions at CERN SPS, BNL RHIC and CERN LHC energies is re-examined in view of the recent studies of Aurenche et al which show that the rate of photon production from quark gluon plasma, evaluated at the order of two loops far exceeds the rates evaluated at one-loop level which have formed the basis of all the estimates of photons so far. We find that the production of photons from quark matter could easily out-shin...

In this talk, I review new developments of QCD calculations of photon and dilepton production rates in a Quark-Gluon plasma. All the rates are now known up to $O(\alpha_s)$ both for photons and dileptons, thanks to the resummation of multiple scatterings. For dileptons, a direct numerical calculation on the lattice attempted recently will also be discussed.

We calculate the production of high energy photons from Compton scattering and annihilation of a quark jet passing through a quark gluon plasma produced in a relativistic heavy ion collision. The contributions are large and reflect the momentum distribution of the jets and the initial conditions of the plasma.

In nucleus-nucleus collisions at relativistic energies a new kind of matter is created, the Quark-Gluon Plasma (QGP). The phase diagram of such matter and the chemical freeze-out points will be presented in connection to the pseudo-critical temperature for the chiral cross over transition. The role of conserved charge fluctuations to give experimental access to the nature of the chiral phase transition will be summarized in terms of the relation to lattice QCD and the current...

Direct photon production from a quark gluon plasma (QGP) in thermal equilibrium is studied directly in real time. In contrast to the usual S-matrix calculations, the real time approach is valid for a QGP that formed and reached LTE a short time after a collision and of finite lifetime ($\sim 10-20 \mathrm{fm}/c$ as expected at RHIC or LHC). We point out that during such finite QGP lifetime the spectrum of emitted photons carries information on the initial state. There is an i...

The recent status of hard thermal photon production in relativistic heavy ion collisions is reviewed and the current rates are presented with emphasis on corrected bremsstrahlung processes in the quark-gluon plasma (QGP) and quark-hadron duality. Employing Bjorken hydrodynamics with an EOS supporting the phase transition from QGP to hot hadron gas (HHG), thermal photon spectra are computed. For SPS 158 GeV Pb+Pb collisions, comparison with other theoretical results and the WA...

We investigate photon production in a scenario of quark-gluon plasma formation in proton-proton scattering at 7 TeV. It is shown that thermal photon yields increase quadratically with the charged particle multiplicity. This gives an enhanced weight to high multiplicity events, and leads to an important photon production even in minimum bias events, where the thermal photons largely dominate over the prompt ones at transverse momentum values smaller than 10 GeV/c.

A systematic investigation of hard thermal photon spectra from central ultra-relativistic heavy ion collisions is presented with emphasis on the effects of bremsstrahlung processes in the quark-gluon plasma (QGP). Bremsstrahlung photon production in the quark-gluon plasma has recently been considered within the Braaten-Pisarski method in thermal QCD, where rates have been found that exhibit the same order in the coupling constants as those describing the lowest order processe...