Radiation-accompanied pion photoproduction on the proton

In the year 1997, Tatischeff et al. found resonance-like states in the invariant mass spectrum of the missing particle X at M=1004, 1044 and 1094 MeV, utilizing the reaction pp→Xpπ+. Investigating the reaction pd→ppX, resonance structures have been observed at M=966, 986 and 1003 MeV in a further experiment by Filkov et al. Such kinds of exotic states contradict various nucleon models which describe the Δ(1232) resonance as the first excited state. Instead, quark cluster models with and without color-magnetic interactions have been formulated to explain these resonance structures. Lvov et al. argued that no such structure had been reported in real Compton scattering data. As a counter argument, Kobushkin suggested that these resonances have a total anti-symmetric spin-flavour wave function and therefore only the N-2γ decay channel is allowed. In this work, the reaction γp→X0π+→nγγπ+ is utilized for the search of these exotic resonances. Data were taken in parallel with the pion polarizability experiment at the MAMI accelerator facility in Mainz. Real photons are created by the bremsstrahlung process of the electrons in a thin radiator foil. Their energy is determined by the A2 photon tagging facility (Glasgow tagger). A 10 cm long liquid hydrogen target was used as a proton target. Charged reaction products are detected in a multi wire proportional chamber in forward direction, at theta <20 s with respect to the beam axis, while secondary photons are detected in the 526 BaF2 crystals containing TAPS spectrometer at polar angles of theta >60 . For neutron detection, a time of flight detector with 111 single modules was used. Additionally, the reaction channels γp→pπ0 and γp→nπ0π+ are analysed to test the apparatuses. For single pion production, differential cross sections are obtained and compared with theoretical models as well as experimental data. For the γp→nπ0π+ channel, invariant mass spectra of particles in the final state are determined and compared with simulation. The data indicate that the main branch of this reaction is a transition via the Δ0(1232) resonance. As a result of searching for exotic resonances, no statistically significant structures have been found. Upper limits for the differential cross sections have been determined