Abstract
The exclusive electroproduction of π+ mesons was studied with the HERMES spectrometer at the DESY laboratory by scattering 27.6 GeV positron and electron beams off an internal hydrogen gas target. The virtual-photon cross sections were measured as a function of the Mandelstam variable t and the squared four momentum −Q2 of the exchanged virtual photon. A model calculation based on Generalized Parton Distributions is in fair agreement with the data at low values of |t| if power corrections are included. A model calculation based on the Regge formalism gives a good description of the magnitude and the t and Q2 dependences of the cross section.
Highlights
The Monte Carlo sample describes the data for values of the squared missing mass higher than 2 GeV2, i.e., outside the region corresponding to exclusive π+ production
The amplitude for exclusive electroproduction of mesons with specific quantum numbers is described by a particular combination of GPDs
Two different types of higher-twist corrections, jointly denoted by the term “power corrections”, have been estimated in the case of π + production [15]: one arising from the intrinsic transverse momentum of the partons, and the other resulting from the softoverlap diagram
Summary
The Monte Carlo sample describes the data for values of the squared missing mass higher than 2 GeV2, i.e., outside the region corresponding to exclusive π+ production. As PYTHIA does not simulate nucleon resonance production, the agreement of the exclusive Monte Carlo sample with the data for the double difference is an indication that there is very little contribution from resonant channels (π + + 0 for π + and π − + ++ for π −) to the normalized-yield difference Nπ+ − Nπ− .
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