hep-ph/9706350

Excess low-energy photon pairs from pion annihilation at the chiral phase transition

Volkov, M.K. (Dubna, JINR) ; Kuraev, E.A. (Dubna, JINR) ; Blaschke, D. (Rostock U.) ; Ropke, G. (Rostock U.) ; Schmidt, S.M. (Tel Aviv U.)

Published in: Phys.Lett.
Year: 1998
Vol.: B424
Page No: 235-243
Pages: 13

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 $\sigma$ meson appears as a bound state in the domain of temperatures and chemical potentials where the condition $M_\sigma(T,\mu) \approx 2 M_\pi(T,\mu)$ is fulfilled. This effect results in a strong enhancement of the cross section for the pion annihilation process $2 \pi \to 2 \gamma$ 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 $\sigma$ meson resonance at threshold due to chiral symmetry restoration.

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