Bochum 1998 – scientific programme

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HK: Hadronen und Kerne

HK 46: Heavy Ion Reactions V, Ultrarelativistic Energies

HK 46.9: Talk

Wednesday, March 18, 1998, 16:45–17:00, P

Measurement of Direct Photons in the WA98 Experiment^* — •D. Bucher¹, C. Barlag¹, S. Bathe¹, C. Blume¹, H. B"usching¹, Z. B"or"ocz¹, R. Glasow¹, S. Gorus¹, S. J"orrens¹, H. K"ohncke¹, T. Kr"umpel¹, T. Peitzmann¹, K. Reygers¹, R. Santo¹, H. Schlagheck¹, and WA98² — ¹Institut f"ur Kernphysik, Universit"at M"unster, D-48149 M"unster — ²

The measurement of direct photons provides a means to look directly into the early phase of the space time evolution of high energy heavy ion collisions and thereby into a possible phase transition to a quark gluon plasma. In addition, it allows to study the emission of photons from hadronic sources in the mixed phase. Unfortunately the signal is overlayed by a large background of photons mainly from π⁰ and η meson decay.

In the WA98 experiment at the SPS reactions of Pb + Pb at 158 A GeV were studied. Photons have been measured by the lead-glass spectrometer LEDA, which provides high spatial and momentum resolution. From the inclusive photon data π⁰ and η meson p_T-spectra are extracted. They are then used as input to a Monte Carlo calculation of the decay photons. The WA98 excess photon p_T-spectra will be shown in comparison with theoretical calculations and results from WA80. They allow the estimation of the initial and critical temperatures of the reaction.
^* Partly supported by the German BMBF and the GSI.