Study of the two pion final state photoproduction on deuterium

Abstract

Understanding the structure of baryons in terms of the fundamental interaction of the constituent quarks and gluons is one of the challenges in strong interaction physics. This interaction is governed by Quantum Chromodynamics (QCD). However, solutions of this theory in the non‐perturbative domain of the interaction are extremely difficult to achieve. In inelastic electron scattering, very little is known about exclusive hadron production purely contributed to a lack of knowledge. The γN interaction is recognized for being a powerful method for investigating hadrons and the mysteries that still exist within the strong interaction. From reactions with the nucleon, the strong interaction can be tested through the amplitudes of the N and Δ resonances. More specifically, if an electromagnetic interaction is well known then the intermediate resonance states may be evaluated through pion photoproduction. To gain more detailed insight into this interaction, we look to probe the baryon structure of Δ and the meson structure of the pion through photon scattering off a deuteron producing two pions in the final state. The photoproduction processes on the deuteron will be used to investigate known baryon resonances in the proton‐pion channel. The two pion final state will be investigated for unraveling new information in to the rho decay at threshold. We want to explore both final states interactions to search for “missing” states that are predicted by quark models but have not yet been found experimentally. Using the CEBAF Large Acceptance Spectrometer (CLAS), the hadronic products are detected in coincidence with the scattered photon. This makes it possible to measure the differential cross section and the decay angular distribution for the production of two and three pion final states. The measured cross sections will contribute significantly and push the knowledge of the strong interaction to the next level. We propose to use the CEBAF Large Acceptance Spectrometer (CLAS) to study the two pion channel from the EG3 data set, for Δ++ (1232) production. We look to investigate the exclusive reaction of γd→pπ+π−(n), extracting the relevant cross sections to comparable data sets. This reaction is produced using a high intensity photon beam incident on a deuterium target. These measurements provide unique and coherent results from tagged photons over a broad range of energy, and represent the only pion production data above 5 GeV at this present time.