Pi NN form factor from QCD sum rules.

Abstract

QCD sum rules are used to calculate the ${\mathit{q}}^{2}$ dependence of the \ensuremath{\pi}NN coupling ${\mathit{g}}_{\mathrm{\ensuremath{\pi}}\mathit{NN}}$(${\mathit{q}}^{2}$) in the spacelike region 0.5 ${\mathrm{GeV}}^{2}$\ensuremath{\lesssim}${\mathit{q}}^{2}$\ensuremath{\lesssim}1.5 ${\mathrm{GeV}}^{2}$. We study the Borel sum rule for the three point function of one pseudo- scalar and two nucleon currents up to order 4 in the operator product expansion. The Borel transform is performed with respect to the nucleon momenta, whereas the momentum ${\mathit{q}}^{2}$ of the pseudoscalar vertex is kept fixed at spacelike values. The results can be well fitted using a monopole form with a cutoff mass of about ${\mathrm{\ensuremath{\Lambda}}}_{\mathrm{\ensuremath{\pi}}}$\ensuremath{\approxeq}800 MeV.