Chemical relaxation time of pions in hot hadronic matter

Abstract

We calculate characteristic time scales for chemical equilibration of pions in hot hadronic matter using an effective chiral Lagrangian. We find that inelastic processes involving the vector and axial vector mesons reduce the chemical equilibration time by a factor of $\sim 10$ compared to the result previously calculated in chiral perturbation theory. For a temperature of $T\sim 150 MeV$ we obtain a chemical relaxation time of $\tau_{ch} \simeq 10 fm/c$, which is comparable with typical time scales for a hadronic system generated in SPS-energy heavy ion collisions. The effect of baryons is also estimated and found to be negligible for SPS-energies but important for AGS-energies. We predict, that chemical freeze-out should take place at considerable higher temperatures $\Delta T \simeq 20 MeV$ than thermal freeze-out and that the hadronic phase would not sustain a pion chemical potential larger than $100 MeV$.Comment: (include Tex source file

Pion Entropy and Phase-Space Densities in <i≯A</i≯+<i≯A</i≯ Collisions

“…Since there is the strong correlation between the initial densities in Some peculiarities of the energy dependence of specific entropy could be associated also with the deficit of pions at highest SPS and probably RHIC energies if one supposes pion chemical equilibrium at chemical freeze-out [9]. The necessary additional contribution can be associated with decays of σ mesons [18]. Due to smaller mass of σ at the phase boundary as compare to its vacuum mass, the chiral phase transition is accompanied by an appearance and subsequent decay at post hadronization stage of a big number of these particles.…”

φmeson propagation in a hot hadronic gas

“…However, it is well known that when the number changing processes are not effective, particle numbers are fixed and chemical potentials associated with these conserved quantities appear [30,31]. For pions and kaons values of µ π = 60 − 80 MeV and µ K = 100 − 130 MeV are reached at freezeout temperatures between 110 and 120 MeV [32].…”

“…Since ρ ↔ ππ is a fast process, one can say that π and ρ mesons are in relative chemical equilibrium i.e. µ ρ = 2µ π [31]. In the case of the ω, a recent calculation has obtained a large collision rate for the reaction ωπ → ππ at high temperatures [33]; therefore, we take µ ω = µ π .…”

K(892)*resonance production in Au+Au andp+pcollisions atAdams1, Aggarwal2, Ahammed3 et al. 2005Phys. Rev. C

“…As the system expands and cools, it will hadronize and chemically freeze out. After a period of hadronic interactions, the system reaches the kinetic freeze-out stage when all hadrons stop interacting [2][3][4]. After the kinetic freeze-out, particles free-stream toward the detectors where our measurements are performed.…”