Direct photons in nuclear collisions at fair energies |
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Authors: | S. M. Kiselev |
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Affiliation: | (1) Institute for Theoretical and Experimental Physics, Moscow, Russia |
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Abstract: | Using the extrapolation of existing data, estimations of prompt-photon production at FAIR energies have been made. At y = y c.m. the rapidity density of prompt photons with p t > 1.5 GeV/c per central Au + Au event at 25 A GeV is estimated as ∼10−4. With the planned beam intensity 109 per second and 1% interaction probability, for 10% of most central events one can expect the prompt-photon rate ∼102 photons per second. Direct photons from the hadron scenario of ion collisions generated by the Hadron-String-Dynamics (HSD) transport approach with implemented meson scatterings πρ → πγ, ππ → ργ have been analyzed. Photons from short-living resonances (e.g., ω → π 0 γ) decaying during the dense phase of the collision should be considered as direct photons. They contribute significantly in the directphoton spectrum at p t = 0.5–1 GeV/c. At the FAIR energy 25 A GeV in Au + Au central collisions the HSD generator predicts, as a lower estimate, γ direct/ ≃ 0.5% in the region p t = 0.5–1 GeV/c. At p t = 1.5–2 GeV/c γ prompt/ ≃ 2%. Thermal direct photons have been evaluated with the Bjorken Hydro-Dynamics (BHD) model. The BHD spectra differ strongly from the HSD predictions. The direct-photon spectrumis very sensitive to the initial temperature parameter T 0 of the model. The 10-MeV increase in the T 0 value leads to ∼2 times higher photon yield. The text was submitted by the authors in English. |
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