Bochum 1998 – wissenschaftliches Programm
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HK: Hadronen und Kerne
HK 59: Heavy Ion Reactions VII, Relativistic Energies
HK 59.2: Gruppenbericht
Donnerstag, 19. März 1998, 14:30–15:00, P
Contribution of π0 and η Dalitz decays to the di-electron invariant-mass spectrum in 1 AGeV heavy-ion collisions — •R. Holzmann1, M. Appenheimer2, R. Averbeck1, Y. Charbonnier3, H. Delagrange3, J. Diaz4, V. Hejny2, S. Hlavac1, A. Kugler5, H. Löhner6, A. Marin1, G. Martinez3, T. Matulewicz3, V. Metag1,2, R. Novotny2, R.W. Ostendorf6, R. Pleskac5, Y. Schutz3, R.S. Simon1, P. Tlusty5, P.H. Vogt6, W. Wagner5, J. Weiß2, H.W. Wilschut6, A.R. Wolf2, and M Wolf2 — 1GSI, Darmstadt — 2Univ. Giessen — 3GANIL, Caen — 4IFC, Valencia — 5NPI, Řež u Prahy — 6KVI, Groningen
The Dalitz-decay contributions of π0 and η mesons to the di-electron invariant-mass spectrum at 1 A GeV have been obtained from a systematics of inclusive meson production cross sections measured with the photon spectrometer TAPS for the collision systems 12C+natC and 40Ar, 40Ca+natCa in the bombarding-energy range of 0.8 – 2.0 A GeV. These results are compared with the recently published di-electron mass spectra of the Dilepton Spectrometer (DLS) collaboration [1]. We find that for Me+e−≤ 0.15 GeV/c2 the mass spectrum is indeed dominated by π0 decays. However, the di-electron yields measured by DLS for masses of 0.15–0.55 GeV/c2 cannot be exhausted by Dalitz decays of η mesons alone and we conclude that, for all A+A systems studied by DLS, additional physical processes are therefore needed to explain the observed set of data.
On the other hand, a comparison of DLS e+e− data for p+p reactions at 1 – 2 GeV [2] with the Dalitz contribution deduced from known p+p η production cross sections yields reasonable agreement for masses ≤ 0.6 GeV/c2.
[1] R.J. Porter et al., Phys. Rev. Lett. 79, 1229 (1997)
[2] W.K. Wilson et al., submitted to Phys. Rev. C