Measurement of the generalized form factors near threshold via $\gamma^* p \to n\pi^+$ at high $Q^2$

Abstract : 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 $\rm{GeV^2}$). 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 $\rm{GeV}$ 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.
Document type :
Journal articles

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Submitted on : Thursday, January 5, 2012 - 9:19:06 AM
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Citation

K. Park, R.W. Gothe, K.P. Adhikari, D. Adikaram, M. Anghinolfi, et al.. Measurement of the generalized form factors near threshold via $\gamma^* p \to n\pi^+$ at high $Q^2$. Physical Review C, American Physical Society, 2012, 85, pp.035208. ⟨10.1103/PhysRevC.85.035208⟩. ⟨in2p3-00656770⟩

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