Eur. Phys. J. A (2014) 50: 146
https://doi.org/10.1140/epja/i2014-14146-2

Regular Article - Theoretical Physics

The pion pole in hard exclusive vector-meson leptoproduction

¹ Bogoliubov Laboratory of Theoretical Physics, Joint Institute for Nuclear Research, 141980, Dubna, Moscow region, Russia
² Fachbereich Physik, Universität Wuppertal, D-42097, Wuppertal, Germany
³ Institut für Theoretische Physik, Universität Regensburg, D-93040, Regensburg, Germany

^* e-mail: kroll@physik.uni-wuppertal.de

Received: 11 July 2014
Accepted: 24 August 2014
Published online: 22 September 2014

Abstract

Exploiting a set of generalized parton distributions (GPDs) derived from analyses of hard exclusive leptoproduction of ρ ⁰, φ and π ⁺ mesons, we investigate the ω spin density matrix elements (SDMEs) recently measured by the HERMES Collaboration. It turns out, from our study, that the pion pole is an important contribution to ω production. It will be treated as a one-particle exchange since its evaluation from the GPD considerably underestimates its contribution. As an intermediate step of our analysis, we extract the πω transition form factor for photon virtualities less than 4 GeV². From our approach we achieve results for the ω SDMEs in good agreement with the HERMES data. The role of the pion pole in exclusive ρ ⁰ and φ leptoproduction is discussed too.