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

Abstract

Particle and photon production is analyzed in the presence of transverse flow using two approximations to describe the properties of the hadronic medium, one containing only π, ρ, ω, and η mesons (simplified equation of state) and the other containing hadrons and resonances from the particle data table. Both are considered with and without initial quark gluon plasma formation. In each case the initial temperature is fixed by requiring dN ch /dy ∼ 550 in the final state.It is shown that most observables are very sensitive to the equation of state. This is particularly evident when comparing the results of the simplified equation of state in the scenarios with and without phase transition. The hadronic gas scenario leads to a substantially higher rate for the pT -distribution of all particles.In the complete equation of state with several hundreds of hadronic resonances, the difference between the scenarios with and without phase transition is rather modest. Both photon and particle spectra, in a wide pT range, show very similar behavior. It is therefore concluded that from the pT spectra it will be hard to disentangle quark gluon plasma formation in the initial state. It is to be stressed however, that there are conceptual difficulties in applying a pure hadronic gas equation of state at SPS-energies. The phase transition scenario with a quark gluon plasma present in the initial state seems to be the more natural one.

Production of intermediate-mass dileptons in relativistic heavy ion collisions

“…Once all parton matter is converted into hadronic matter, we assume the hot hadronic system to continue to expand until it undergoes a freeze-out at some temperature T F . During this evolution, the speed of sound of the matter is consistently calculated at every temperature to be used in the equation of state needed for solving the hydrodynamic equations [17].…”

“…[1] F. Karsch,17 th International Symposium on Lattice Field Theory (Lattice '99), Pisa, Italy, hep-lat/9909006.…”

Direct photon production in heavy-ion reactions at SPS and RHIC

“…Using the relatively light ion beams of 16 O and 32 S at a beam energy of 200 A GeV, corresponding to a nucleon-nucleon center of mass energy of √ s N N = 19.4 GeV, the experiments WA80 [5,6], HELIOS (NA34) [7] and CERES (NA45) [8] have attempted to measure direct photons. All these measurements have been able to deliver upper limits of direct photon production.…”

“…HELIOS has studied p-, 16 O-and 32 S-induced reactions [7] with a conversion method. The authors estimate the ratio of the integrated yields of inclusive photons and neutral pions:…”

Bremsstrahlung radiation as a coherent state in thermal QED

“…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].…”