DPG Phi
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Münster 2002 – scientific programme

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HK: Physik der Hadronen und Kerne

HK 20: Heavy Ions II

HK 20.4: Talk

Tuesday, March 12, 2002, 18:00–18:15, E

Direct Measurement of Delta Production in 40Ar + natCa at 0.8A GeV — •Ana Marin — Gesellschaft für Schwerionenforschung, D-64291 Darmstadt, Germany

Charged pions and protons can be identified in the modularized photon spectrometer TAPS if one restricts the analysis to isolated BaF2 crystals in the hit response and if one correlates time–of–flight and deposited energy. This method is exploited in 40Ar+natCa at 0.8A GeV to investigate the production of Δ(1232) resonances in the rapidity range 0.2<y<0.4 and for transverse momenta 90 MeV/c<pt<800 MeV/c via the invariant–mass reconstruction of the pπ decay products. The inclusive Δ mass distribution (83% Δ++, 17% Δ0) is shifted to 1206 MeV, while we obtain a Δ++ cross section of 190 ± 30 mbarn in 4π, given a temperature of 50±8 MeV of the fireball derived from the Δ pt distribution and assuming isotropic emission. Comparison to the simultaneously measured π0 yield results in Δ++0 = 0.155±0.013. This is well below the value of 0.675 expected from the isobar model and shows that only a minority of the pions is still bound in resonances at thermal freeze–out.

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