FIZIKA B 8 (1999) 1, 51-54

LETTER TO THE EDITOR

THE AXIAL FORM FACTOR OF THE NUCLEON FROM ELECTRO-PION PRODUCTION AT LOW q²

Complete results of this measurement will be published elsewhere by A. Liesenfeld et al.

M. POTOKAR^a (A1 COLLABORATION AT MAMI)

^aJožef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia

Received 25 January 1999, Accepted 12 July 1999

Results of the measurement of the transverse and longitudinal cross section for coincident electro-production of positively charged pions on protons measured in parallel kinematics at the invariant mass of W = 1125 MeV and at three four-momentum transfers q² = -0.117, -0.195 and -0.273 (GeV/c)² are presented. An axial-mass parameter of high accuracy was extracted from a preliminary analysis of the transverse cross section within the Mainz effective Lagrangian model of the nucleon. The value supports the prediction of the chiral perturbation theory that pion-loop corrections effectively increase the value of the axial mass extracted from pion electro-production data relative to that from neutrino scattering.

PACS numbers: 13.60.Le, 14.20.Dh
UDC 539.125, 539.126

Keywords: axial dipole mass, axial form factor, pion electro-production

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