K. P. Adhikari

We report the first extraction of the pion-nucleon multipoles near the production threshold for the $n{\pi }^{+}$ channel at relatively high momentum transfer ($Q^2$ up to 4.2 ${\mathrm{GeV}}^2$). The dominance of the $s$-wave transverse multipole ($E_{0+}$), expected in this region, allowed us to access the generalized form factor $G_1$ within the light-cone sum-rule (LCSR) framework as well as the axial form factor $G_A$. The data analyzed in this work were collected by the nearly $4\pi$ CEBAF Large Acceptance Spectrometer (CLAS) using a 5.754-GeV electron beam on a proton target. The differential cross section and the $\pi$-$N$ multipole $E_{0+}/G_D$ were measured using two different methods, the LCSR and a direct multipole fit. The results from the two methods are found to be consistent and almost $Q^2$ independent.

We have measured the differential cross section for the $\gamma$ ${}^3\mathrm{He}$ $\to \pi {}^{+}t$ reaction. This reaction was studied using the Continuous Electron Beam Accelerator Facility (CEBAF) Large Acceptance Spectrometer (CLAS) at Jefferson Lab. Real photons produced with the Hall-B bremsstrahlung tagging system in the energy range from 0.50 to 1.55 GeV were incident on a cryogenic liquid ${}^3\mathrm{He}$ target. The differential cross sections for the $\gamma$ ${}^3\mathrm{He}$ $\to \pi {}^{+}t$ reaction were measured as a function of photon-beam energy and pion-scattering angle. Theoretical predictions to date cannot explain the large cross sections except at backward angles, showing that additional components must be added to the model.