We report the first extraction of the pion-nucleon multipoles near the production threshold for the nπ+ channel at relatively high momentum transfer (Q2 up to 4.2 GeV2). The dominance of the s-wave transverse multipole (E0+), expected in this region, allowed us to access the generalized form factor G1 within the light-cone sum-rule (LCSR) framework as well as the axial form factor GA. The data analyzed in this work were collected by the nearly 4π CEBAF Large Acceptance Spectrometer (CLAS) using a 5.754-GeV electron beam on a proton target. The differential cross section and the π-N multipole E0+/GD 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 Q2 independent.
Physical Review C
Park, K.; Biselli, Angela; and CLAS Collaboration, "Measurement of the generalized form factors near threshold via γ∗p→nπ+ at high Q2" (2012). Physics Faculty Publications. 35.
K. Park et al. [CLAS Collaboration], "Measurement of the generalized form factors near threshold via γ∗p→nπ+ at high Q2," Physical Review C 85.3 (2012) DOI: 10.1103/PhysRevC.85.035208