Excess low energy photon pairs from pion annihilation at the chiral phase transition
arXiv:hep-ph/9706350 · doi:10.1016/S0370-2693(98)00227-5
Abstract
The photon pair production by pion annihilation in a hot and dense medium at the chiral phase transition is investigated within a chiral quark model. As a direct consequence of this transition the $Ï$ meson appears as a bound state in the domain of temperatures and chemical potentials where the condition $M_Ï(T,μ) \approx 2 M_Ï(T,μ)$ is fulfilled. This effect results in a strong enhancement of the cross section for the pion annihilation process $2 Ï\to 2 γ$ compared with the vacuum case. The calculation of the photon pair production rate as function of the invariant mass shows a strong enhancement and narrowing of the $Ï$ meson resonance at threshold due to chiral symmetry restoration.
15 pages, LaTeX, 6 figures, Phys. Lett. B