| Irfu-08-30
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| Cross sections and beam asymmetries for vec(e) p -> en pi+ in the nucleon resonance region for 1.7 <= Q**2 <= 4.5-(GeV)**2 |
| K. Park et al (R. de Masi, M. Garçon, F.X. Girod, J.M. Laget, L. Morand, S. Morrow, F. Sabatié) |
| The exclusive electroproduction process $\\vec{e}p \\to e^\\prime n \\pi^+$ was measured in the range of the photon virtuality $Q^2 = 1.7 - 4.5 \\rm{GeV^2}$, and the invariant mass range for the $n\\pi^+$ system of $W = 1.15 - 1.7 \\rm{GeV}$ using the CEBAF Large Acceptance Spectrometer. For the first time, these kinematics are probed in exclusive $\\pi^+$ production from protons with nearly full coverage in the azimuthal and polar angles of the $n\\pi^+$ center-of-mass system. The $n\\pi^+$ channel has particular sensitivity to the isospin 1/2 excited nucleon states, and together with the $p\\pi^0$ final state will serve to determine the transition form factors of a large number of resonances. The largest discrepancy between these results and present modes was seen in the $\\sigma_{LT\'}$ structure function. In this experiment, 31,295 cross section and 4,184 asymmetry data points were measured. Because of the large volume of data, only a reduced set of structure functions and Legendre polynomial moments can be presented that are obtained in model-independent fits to the differential cross sections. |
