Photoproduction of Pion Pairs - Reaction Mechanisms for $\gamma p\rightarrow n\pi^0\pi^+$

This work analysed the reaction channel of mixed charged pion pairs of the free proton and presents measurements for total cross sections, angular distributions and invariant mass distributions for the reaction channel of $\gamma p \rightarrow \pi^0 \pi^+ n$.\\
Its aim is to deepen the knowledge on the excitation resonances of nucleons and reduce the still leaping gap between theoretically predicted and experimentally affirmed excitation states.
The data analysed in this work was measured at MAMI with the A2 detector setup in April 2009, situated in Mainz, Germany.
Photons tagged by the Glasgow Photon Tagger, impinging on a liquid hydrogen target, surrounded by the calorimeters Crystal Ball, and the forward wall TAPS, covering almost $4\pi$, were used to measure the energies of the final state particles.
Charged particles were identified using the Particle Identification Detector, enclosing the Target, within the Crystal Ball and the veto detectors in front of TAPS.\\
Specialized analysis software, based on the CERN ROOT framework was used and refined for the presented spectra of total cross section and differential cross sections of angular distributions of combined meson polar angles in centre of momentum frame and invariant mass distributions all three final state participant participle pairs.\\
The four different reaction contributions of Monte Carlo simulations for the determined detection efficiency corrections, allow a glance on the branching ratio of underlying reaction composition of the analysed reaction channel.\\
Results for total cross sections, and differential cross section are presented in unprecedented resolution and precision for energies above the first resonance peak, expanding the range of experimentally measured cross-section data for the analysed reaction channel to 1450 MeV $E_\gamma$.\\
The obtained results are compared to meson photoproduction models and previously published results.