FIZIKA B 8 (1999) 1, 51-54

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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. POTOKARa (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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