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HK: Hadronen und Kerne
HK 27: Hadronic Probes III, Particle Production
HK 27.1: Group Report
Tuesday, March 17, 1998, 14:00–14:30, C
Exclusive bremsstrahlung and pion production in proton-nucleus reactions — •M.J. van Goethem1, L. Aphecetche2, J.C.S. Bacelar1, D. d’Enterría2, M.N. Harakeh1, M. Hoefman1, R. Holzmann3, H. Huisman1, N. Kalantar-Nayestanaki1, A. Kugler4, H. Löhner1, G. Martínez2, J.G. Messchendorp1, R.W. Ostendorf1, S. Schadmand1,5, Y. Schutz2, M. Seip1, R.H. Siemssen1, P. Tlustý4, M. Volkerts1, V. Wagner4, and H.W. Wilschut1 — 1KVI Groningen — 2GANIL Caen — 3GSI Darmstadt — 4NPI Řež u Prahy — 5Univ. Giessen
Nuclear bremsstrahlung has been studied in reactions of 190 MeV protons from AGOR with light and heavy nuclear targets. Bremsstrahlung originates dominantly from proton–neutron collisions and thus provides a clean probe of the reaction dynamics. Proton-induced reactions are a suitable testing ground for the influence of the nuclear medium on the bremsstrahlung process. In particular, we aim to study the influence of multiple scattering, the effect of coherence, and the mean-field on the photon production yield and the spectral distribution. Since photon amplitudes from subsequent steps in the multiple scattering process add coherently, this will lead to quenching of the soft-photon yield.
The Two-Arm Photon Spectrometer (TAPS) was employed to measure photons in coincidence with recoil neutrons and scattered protons. Protons and neutrons scattered at forward angles were detected by the Small-Angle Large-Acceptance Detector SALAD. This exclusive study allows to determine the momentum transfer in the scattering process and thus to enhance the sample of photons originating from multiple scattering. The photon contribution from neutral-pion production is considerable and has been analyzed. The dependence of subthreshold π0 production on the size of the reaction system will be discussed. Photon spectra in coincidence with scattered neutrons and protons at various angles have been studied. Preliminary data show a suppression of the soft-photon yield in the multiple scattering regime i.e. for large neutron scattering angles. The significance of this observation for the expected quenching due to coherent photon production will be discussed.