Köln 2004 – scientific programme

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HK: Physik der Hadronen und Kerne

HK 5: Theory I

HK 5.7: Talk

Monday, March 8, 2004, 17:30–17:45, D

Low energy double-pion photoproduction and pion absorption in nuclei — •Luis Alvarez-Ruso, Oliver Buss, Ulrich Mosel, and Pascal Mühlich — Institut für Theoretische Physik, Universität Giessen, 35392 Giessen, Germany

We investigate π⁰ π⁰ and π^± π⁰ photoproduction off nuclei at incident beam energies of 400-460 MeV. For the pion-pair production on the nucleons we use a theoretical model developed in Valencia (Nacher et al.). A full coupled-channel treatment of final state interactions is performed by means of the semi-classical BUU transport model. We observe that quasi-elastic and charge-exchange scatterings of the final state pions with the nucleons of the surrounding medium cause a downward shift of the π π invariant mass distributions. In the π⁰ π⁰ channel, our results agree well with the data on ¹²C and ²⁰⁸Pb obtained recently at MAMI-B without introducing any additional in-medium modification. In the π^± π⁰ channel, however, we overestimate the total cross-section. Furthermore, we study the role of the real part of the pion optical potential in the pion propagation inside nuclei within our semi-classical model. The aim is to describe simultaneously low-energy pion absorption and double-pion photoproduction in nuclei.
Work supported by the Humboldt foundation and the European graduate school Giessen–Copenhagen.