Double Pion Photoproduction off nuclei - search for the in-medium modification of the σ-meson
Department of Physics, University of Basel, CH-4056 Basel, Switzerland
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The photoproduction of π0π0 and π0π+/− pairs has been investigated in view of the of in-medium modifications the σ-meson. The measurements have been done at the Mainz MAMI accelerator, using the Glasgow photon tagging spectrometer and a 4π electromagnetic calorimeter, consisting of the Crystal Ball and TAPS detectors. The measurements covered different nuclear targets (2H, 7Li, 12C, 40Ca, and natPb) and the statistical quality of the data was improved compared to the previous experiments. The energy and mass dependence of the invariant mass distributions suggests that Final State Interactions play a very important role, but some of the observed effects can also be related to a possible in-medium modification of the σ-meson.
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