Positive Pion Photoproduction Near Threshold

Abstract: Pion photo production from the nucleon is an important process utilized to understand the structure of the nucleon and the fundamental dynamics of the nucleon system. The neutral pion production has been extensively studied resulting in valuable data sets. However, much less data is available for charged pion photo production at energies below 200 MeV. In order to get a reliable data set for π+, for the energy range from threshold to the Δ-resonance production, a photonuclear reaction (γ + p → n + π+) experiment was conducted at Max-lab. In the experiment a photon beam with energies from 169 to 180 MeV passed a circular collimator and hit a target (C, Ta). Charged Pions were produced well below threshold. The data was stored in Root-tree files and analyzed using C++ programing codes. The technique to identify in the experiment was based on probing the 26 ns decay in Scintillator Range Telescopes. The differential cross section for π+ as well as for protons was determined. The results are consistent with the theoretical predictions and measurements performed by experts at Max-lab.