Coherent $\pi^+$ Photoproduction on $^3$He

Comparing an elementary meson-production process on a free nucleon with the same process inside a nucleus has been an interesting problem in nuclear physics. Studying these processes are useful in developing our understanding of nuclear structure and the long-range part of the nucleon-nucleon interaction described by the one-pion-exchange model. In the present analysis, we have measured the differential cross section for the $\gamma$$^3$He$\rightarrow \pi^+ t$ reaction channel. Studying this channel is ideal for understanding the interaction of pions with nuclei and for searching for possible effects mediated by nucleon resonances in nuclear matter. The $^3$He target contains the lightest nucleus on which one can observe coherent (elastic) $\pi^+$ photoproduction with charge exchange that also leads to a well defined final state that can be easily identified. This reaction was studied using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab. Real photons produced with the Hall-B bremsstrahlung tagging system in the energy range from 0.35 to 1.55 GeV were incident on a cryogenic liquid $^3$He target. The differential cross sections for the $\gamma$$^3$He$\rightarrow \pi^+ t$ reaction were measured as a function of photon-beam energy and pion-scattering angle in the center-of-mass frame. Our results will be presented and discussed.