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Low-Energy Thermal Photons from Meson-Meson Bremsstrahlung

W. Liu·R. Rapp
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Abstract

Within an effective hadronic model including electromagnetic interactions via a U$_{\rm em}$(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 $ππ\toππγ$ and $πK \toπKγ$ 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 "$σ$" and $ρ$-meson exchanges are briefly discussed.

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W. Liu, R. Rapp. 2007-09-04. Low-Energy Thermal Photons from Meson-Meson Bremsstrahlung. https://doi.org/10.1016/j.nuclphysa.2007.08.014

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