Low-Energy Thermal Photons from Meson-Meson Bremsstrahlung

Abstract

Within an effective hadronic model including electromagnetic interactions via a U${}_{\mathrm{em}}$(1) gauge, we reinvestigate photon Bremsstrahlung from a hot hadronic gas as expected to be formed in relativistic heavy-ion collisions at SPS energies. We calculate photon emission from the reactions $\pi \pi \to \pi \pi \gamma$ and $\pi K\to \pi K\gamma$ by an explicit (numerical) evaluation of the multi-dimensional phase space integral. This, in particular, allows to avoid the commonly employed soft photon approximation (SPA), as well as to incorporate final-state thermal enhancement factors. % during the hadronic stage of the fireball. Both improvements are shown to result in an appreciable increase of the photon production rate over previous hadronic calculations. Upon convolution over a thermal fireball we find an improvement in the description of recent low transverse-momentum WA98 data at SPS. The influence of both Landau-Pomeranchuk-Migdal and in-medium effects on "$\sigma$" and $\rho$-meson exchanges are briefly discussed.

arXiv commentversion to appear in Nucl. Phys. A

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