Measurement of the generalized form factors near threshold via ${\gamma }^{\ast }p\to n{\pi }^{+}$ 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 $\mathrm{Ge}{\mathrm{V}}^2$). 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 $\mathrm{GeV}$ 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.

17pages, 22 figures, Journal article (Physical Review C)

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• Unitary Isobar Model - MAID2007
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• Nucleon electromagnetic form factors and polarization observables in space-like and time-like regions
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