arXiv subjects
Publications and source records attributed to K. Redlich.
We calculate the time evolution of fluctuations for rare particles such as e.g. kaons in 1 AGeV or charmonium in 200 AGeV heavy ion collisions. We find that these fluctuations are a very sensitive probe of the degree of chemical equilibration reached in these collisions. Furthermore, measuring the second factorial moment the size of the initial population can be determined.
A systematic study is performed of fully integrated particle multiplicities in central Au-Au and Pb-Pb collisions at beam momenta of 1.7A GeV, 11.6A GeV (Au-Au) and 158$A$ GeV (Pb-Pb) by using a statistical-thermal model. The close similarity of the colliding systems makes it possible to study heavy ion collisions under definite initial conditions over a range of centre-of-mass energies covering more than one order of magnitude. In order to further study the behaviour of strangeness production, an updated study of Si-Au collisions at 14.6A GeV is also presented. The data analysis has been performed with two completely independent numerical algorithms giving closely consistent results. We conclude that a thermal model description of particle multiplicities, with additional strangeness suppression, is possible for each energy. The degree of chemical equilibrium of strange particles and the relative production of strange quarks with respect to u and d quarks are higher than in e+e-, pp and ppbar collisions at comparable and even at lower energies. The behaviour of strangeness production as a function of centre-of-mass energy and colliding system is presented and discussed. The average energy per hadron in the comoving frame is close to 1 GeV per hadron despite the fact that the energy increases more than 10-fold.
Results of a systematic study of fully integrated particle multiplicities in central Au-Au and Pb-Pb collisions at beam momenta 1.7 A GeV, 11.6 A GeV (Au-Au) and 158 A GeV (Pb-Pb) using a statistical-thermal model are presented. The close similarity of the colliding systems makes it possible to study heavy ion collisions under definite initial conditions over a range of centre-of-mass energies covering more than one order of magnitude. We conclude that a thermal model description of particle multiplicities, with additional strangeness suppression, is possible for each energy. The degree of chemical equilibrium of strange particles and the relative production of strange quarks with respect to u and d quarks are higher than in e+e-, pp and pp(bar) collisions at comparable and even at lower energies. The average energy per hadron in the comoving frame is always close to 1 GeV per hadron despite the fact that the energy varies more than 10-fold.
It is demonstrated that there exists a direct correlation between chemical freeze-out point and the softest point of the equation of state where the pressure divided by the energy density, $p(ε)/ε$, has a minimum. A dynamical model is given as an example where the passage of the softest point coincides with the condition for chemical freeze-out, namely an average energy per hadron $\approx$ 1 GeV. The sensitivity of the result to the equation of state used is discussed.
We formulate the kinetic master equation describing the production of charged particles which are created or destroyed only in pairs due to the conservation of their Abelian charge.Our equation applies to arbitrary particle multiplicities and reproduces the equilibrium results for both canonical (rare particles) and grand canonical (abundant particles) systems. For canonical systems, the equilibrium multiplicity is much lower and the relaxation time is much shorter than the naive extrapolation from the grand canonical ensemble results. Implications for particle chemical equilibration in heavy-ion collisions are discussed.
The excitation functions of $K^+$ and $K^-$ mesons in heavy ion collisions are studied within a statistical model assuming chemical and thermal equilibrium with exact strangeness conservation. At low incident energies the associate production of kaons, i.e. the production of a K+ together with a hyperon and the production of a K- together with a K+, implies specific features: different threshold energies and different dependences of K+ and K- yields on baryon number density. It is shown that the experimentally observed equality of the $K^+$ and $K^-$ rates at energies $\sqrt{s} - \sqrt{s_{th}} \leq 0$ is due to a crossing of the two excitation functions. Furthermore, the independence of the $K^+$ to $K^-$ ratio on the number of participating nucleons observed at 1 and 10 $A\cdot$GeV is consistent with this model.
Using J/psi and open charm photoproduction data, we apply the vector meson dominance model to obtain constraints on the energy dependence of the inelastic J/psi-nucleon cross section. Predictions of short distance QCD are in accord with these constraints, while recently proposed hadronic models for J/psi dissociation strongly violate them.
We consider the charmonium production in thermalized hadronic medium created in ultrarelativistic heavy ion collisions at LHC energy. The calculations for the secondary $J/ψ$ and $ψ^,$ production by $D\bar D$ annihilation are performed within a kinetic model taking into account the space-time evolution of a longitudinally and transversely expanding medium. We show that the secondary charmonium production appears almost entirely during the mixed phase and it is very sensitive to the charmonium dissociation cross section with co-moving hadrons. Within the most likely scenario for the dissociation cross section of the $J/ψ$ mesons their regeneration in the hadronic medium will be negligible. The secondary production of $ψ^,$ mesons however, due to their large cross section above the threshold, can substantially exceed the primary yield.
We compute the pressure of a finite density quark-gluon plasma at zero temperature to leading order in hard-thermal-loop perturbation theory, which includes the fermionic excitations and Landau damping. The result is compared with the weak-coupling expansion for finite positive chemical potential $μ$ through order $α_s^2$ and with a quasiparticle model with a mass depending on $μ$.
Within the Closed Time Path Formalism of Thermal Field Theory we calculate the hard photon emission rate as well as the collisional energy-loss rate for a quark-gluon plasma away from chemical equilibrium. Mass singularities are shown to be dynamically screened within HTL-resummed perturbation theory also away from equilibrium. Additional (pinch) singularities are absent and well defined results are obtained.
We consider the production of charmonium by $D\bar D$ annihilation during the mixed and hadronic phase of Pb-Pb collision at LHC energy. The calculations for secondary $J/ψ$ and $ψ^,$ production are performed within a kinetic model taking into account the space-time evolution of a longitudinally and transversely expanding medium. It is shown that the yield of secondary $J/ψ$ mesons depends strongly on the $J/ψ$ dissociation cross section with co-moving hadrons. Within the most likely scenario for the dissociation cross section it will be negligible. The secondary production of $ψ^,$ mesons, however, due to their large cross section above the threshold, can substantially exceed the primary yield.
The present knowledge about hadrons produced in relativistic heavy ion collisions is compatible with chemical freeze-out happening when the energy density divided by the particle density reaches the value of 1 GeV. This observation is used to determine the energy dependence of the chemical freeze-out parameters T_{ch} and mu_B^{ch} for beam energies varying between 1 and 200 A.GeV. The consequences of this energy dependence are studied for various particle ratios. Predictions for particle ratios at beam energy 40 A.GeV are presented. The conditions for thermal freeze-out are also determined. These correspond either to an energy density of 45 MeV/fm**3 or to a particle density of 0.05/fm**3.
It is shown that the chemical freeze-out parameters obtained at CERN/SPS, BNL/AGS and GSI/SIS energies all correspond to a unique value of 1 GeV for the average energy per hadron.
It is shown that the condition for chemical freeze-out, average energy per hadron approximately 1 GeV, selects the softest point of the equation of state, namely the point where the pressure divided by the energy density has a minimum. The sensitivity to the equation of state used is discussed. The previously proposed mixed phase model, which is consistent with lattice QCD data naturally leads to the chemical freeze-out condition.
Ratios of integrated particle yields provide the best method for determining the temperature and the chemical potential. The chemical freeze-out parameters obtained at CERN/SPS, BNL/AGS and GSI/SIS energies all correspond to a unique value of 1 GeV per hadron in the local rest frame of the system, independent of the beam energy and of the target and beam particles.
Attention is drawn to the role played by the size of the system in the thermodynamic analysis of particle yields in relativistic heavy ion collisions at SIS energies. This manifests itself in the non-linear dependence of K+ and K- yields in $AA$ collisions at 1 -- 2 A.GeV on the number of participants. It is shown that this dependence can be quantitatively well described in terms of a thermal model with a canonical strangeness conservation. The measured particle multiplicity ratios (pi+/p, pi-/pi+, d/p, K+/pi+ and K+/K- but not eta/pi0) in central Au-Au and Ni-Ni collisions at 0.8 -- 2.0 A.GeV are also explained in the context of a thermal model with a common freeze-out temperature and chemical potential. Including the concept of collective flow a consistent picture of particle energy distributions is derived with the flow velocity being strongly impact-parameter dependent.
We investigate the production rate for hard real photons and the collisional energy loss in the quark-gluon plasma away from chemical equilibrium. Applying the Hard-Thermal-Loop resummation scheme away from equilibrium, we can show that Landau damping provides dynamical screening for both fermion and boson exchange present in the two quantities.
It is shown that the chemical freeze-out parameters obtained at CERN/SPS, BNL/AGS and GSI/SIS energies all correspond to a unique value of 1 GeV per hadron in the local rest frame of the system, independent of the beam energy and of the target and beam particles.