Hydrodynamical description of200AGeV/cS+Au collisions: Hadron and electromagnetic spectra

Abstract

We study relativistic SϩAu collisions at 200A GeV/c using a hydrodynamical approach. We test various equations of state ͑EOS's͒, which are used to describe the strongly interacting matter at densities attainable in the CERN-SPS heavy ion experiments. For each EOS, suitable initial conditions can be determined to reproduce the experimental hadron spectra; this emphasizes the ambiguity between the initial conditions and the EOS in such an approach. Simultaneously, we calculate the resulting thermal photon and dielectron spectra, and compare with experiments. If one allows the excitation of resonance states with increasing temperature, the electromagnetic signals from scenarios with and without phase transition are very similar and are not resolvable within the current experimental resolution. Only EOS's with a few degrees of freedom up to very high temperatures can be ruled out presently. We deduce an upper bound of about 250 MeV for the initial temperature from the single photon spectra of WA80. With regard to the CERES dilepton data, none of the EOS's considered, in conjunction with the standard leading order dilepton rates, succeed in reproducing the observed excess of dileptons below the peak. Our work, however, suggests that an improved measurement of the photon and dilepton spectra has the potential to strongly constrain the EOS.

ρ→ππ decay in nuclear medium

“…In this context, the properties of vector mesons (especially of the ρ) in a hadronic environment become of particular interest, since the Vector Meson Dominance Model is commonly used to make the estimates of the dilepton yields from vector-meson decays. There are numerous analysis of the effect in the literature, both in hydrodynamic approaches [42,70,71,72,73], and in transport theories [13,74,75,76,77,78,79,80]. The dilepton-rate formula [81,82,83,84,85] from ρ meson decays can be written in a manifestly Lorentz covariant way as follows:…”

Thermal particle and photon production in Pb+Pb collisions with transverse flow

“…The evidence is mainly "circumstantial" [1], however, in all recent analyses of particle ratios it is impossible to ignore transverse flow without running into contradictions [2][3][4][5][6]. There has therefore been a lot of interest recently in analyzing the effects of flow more thoroughly [7][8][9][10].…”

Bremsstrahlung radiation as a coherent state in thermal QED

“…(5), ℜ(X) can be divided into two parts, one part is the same as obtained in quantum field theory and another part is the contribution of the thermal effects. Both parts are all infrared divergent and give negative contribution comparing to the real emission (5) and absorption (8).…”

“…A lot of fruitful theoretical investigations have been made on the signals for the existence of the QGP, for example, J/Ψ suppression [1], strangeness enhancement [2], jet quenching [3], dilepton and thermal photon production [4] etc. As the electromagnetic signal of the QGP the production of the thermal photon has been investigated by calculating the Compton scattering and qq-annihilation processes in the QGP state [5][6][7][8][9]. Recent research [10] shows a very interesting result: the bremsstrahlung processes in the QGP state play an important role in the thermal photon production, it generates contribution of the same order of magnitude as Compton scattering and qq-annihilation processes based on the resummation of hard thermal loops [11].…”