Bochum 1998 – scientific programme

Parts | Days | Selection | Search | Downloads | Help

HK: Hadronen und Kerne

HK 59: Heavy Ion Reactions VII, Relativistic Energies

HK 59.2: Group Report

Thursday, March 19, 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. Metag^1,2, 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 M_e⁺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