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arXiv · hep-ph/9706350

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

M. K. Volkov·E. A. Kuraev·D. Blaschke·G. Roepke·S. Schmidt
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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 $σ$ meson appears as a bound state in the domain of temperatures and chemical potentials where the condition $M_σ(T,μ) \approx 2 M_π(T,μ)$ is fulfilled. This effect results in a strong enhancement of the cross section for the pion annihilation process $2 π\to 2 γ$ 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 $σ$ meson resonance at threshold due to chiral symmetry restoration.

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M. K. Volkov, E. A. Kuraev, D. Blaschke, G. Roepke, S. Schmidt. 1998-02-05. Excess low energy photon pairs from pion annihilation at the chiral phase transition. https://doi.org/10.1016/s0370-2693(98)00227-5

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