München 2006 – wissenschaftliches Programm
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HK: Physik der Hadronen und Kerne
HK 8: Elektromagnetische und Hadronische Sonden
HK 8.4: Vortrag
Montag, 20. März 2006, 17:15–17:30, F
π π photoproduction and the mean free path of pions — •Oliver Buss, Luis Alvarez-Ruso, Ulrich Mosel und Pascal Mühlich — Institut für Theoretische Physik, Universität Giessen, Germany
A method to describe the scattering of low-energy pions with nuclei within a BUU transport model is presented. Considerable interest in such low-energy events has been triggered by recent respectively ongoing π π production experiments by the TAPS and by the CHAOS collaborations, which both reported an effect which was interpreted as an in-medium modification of the σ-meson. In these experiments the σ-resonance is excited in nuclei and it decays inside the nuclear medium into a low-energetic two-pion final-state. The description of low-energy pions becomes therefore critical in the analysis of the final-state effects of the latter experiments.
Implementing different scenarios of medium modifications, the mean
free path of pions in nuclear matter at low momenta and pion
absorption reactions on nuclei were studied and compared to data and
to results obtained via quantum mechanical scattering theory. Pursuing
these studies it was shown, that also in a regime of a long pionic
wave length the semi-classical transport model still generates
reasonable results. Results are presented for nuclear matter
calculations, π-nucleus events in the regime of 10 MeV≤
Tkinπ≤ 150 MeV and for photon-induced π π
production off nuclei at incident beam energies of 400−500 MeV.
Utilising only standard rescattering and absorption effects in the
analysis of ππ-photoproduction reactions, we observe a downward
shift of the invariant mass of the π π-pairs when going from
light to massive nuclei.
Supported by DFG.