Münster 2017 – scientific programme

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HK: Fachverband Physik der Hadronen und Kerne

HK 38: Hadron Structure and Spectroscopy V

HK 38.4: Talk

Thursday, March 30, 2017, 15:00–15:15, F 5

Photoproduction of π⁰π⁺ Pairs off the free Proton — •Samuel Abt for the A2 collaboration — Departement Physik, Universität Basel

Photoproduction of mesons has been intensively studied during the last decade in view of the nucleon resonance spectrum. Beside single meson production reactions, final states with meson pairs have gained a lot of interest. For free nucleons, such final states can be used to study sequential decays of nucleon resonances via intermediate excited states and determine their branching ratios. Especially for channels with π⁺π⁰ and π⁺π⁻ pairs, also resonance decays by emission of the ρ- meson can be studied. The presented work investigates in detail the total cross section, invariant mass distributions, and angular distributions of the γ p → π⁰ π⁺ n reaction up to incident photon energies of 1.5 GeV. The experiment was carried out at the tagged photon beam of the Mainz MAMI accelerator. The bremsstrahlung photon beam was impinging on a liquid hydrogen target and the pions and the recoil neutron were detected with the combined electromagnetic calorimeters Crystal Ball and TAPS detectors. The most striking finding is a strong contribution of the D₁₃(1520)→ Nρ branch (comparably large as D₁₃(1520)→ Δπ). The data will provide a precise branching ratio for this reaction. Preliminary results will be discussed.