A measurement of the axial form factor of the nucleon by the p(e,e′ π+)n reaction at [formula omitted]

• Published in: Physics letters. B 1999-11, Vol.468 (1), p.20-27
• Main Authors: Liesenfeld, A., Richter, A.W., Širca, S., Blomqvist, K.I., Boeglin, W.U., Bohinc, K., Böhm, R., Distler, M., Drechsel, D., Edelhoff, R., Ewald, I., Friedrich, J., Friedrich, J.M., Geiges, R., Kahrau, M., Korn, M., Krygier, K.W., Kunde, V., Merkel, H., Merle, K., Müller, U., Neuhausen, R., Pospischil, T., Potokar, M., Rokavec, A., Rosner, G., Sauer, P., Schardt, S., Schmieden, H., Tiator, L., Vodenik, B., Wagner, A., Walcher, Th, Wolf, S.
• Format: Article
• Language: English
• Subjects: Coincident pion electroproduction; Nucleon axial form factor
• ISSN: 0370-2693; 1873-2445
• DOI: 10.1016/S0370-2693(99)01204-6

The reaction p(e,e′ π +)n was measured at the Mainz Microtron MAMI at an invariant mass of W=1125 MeV and four-momentum transfers of Q 2=0.117, 0.195 and 0.273 ( GeV/c) 2 . For each value of Q 2, a Rosenbluth separation of the transverse and longitudinal cross sections was performed. An effective Lagrangian model was used to extract the `axial mass' from experimental data. We find a value of M A =(1.077±0.039) GeV which is (0.051±0.044) GeV larger than the axial mass known from neutrino scattering experiments. This is consistent with recent calculations in chiral perturbation theory.