Abstract
The exclusive electroproduction of π + above the resonance region was studied using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Laboratory by scattering a 6GeV continuous electron beam off a hydrogen target. The large acceptance and good resolution of CLAS, together with the high luminosity, allowed us to measure the cross section for the γ * p → nπ + process in 140 (Q 2, x B , t) bins: 0.16 < x B < 0.58, 1.6 GeV2 < Q 2 < 4.5 GeV2 and 0.1 GeV2 < −t < 5.3 GeV2. For most bins, the statistical accuracy is on the order of a few percent. Differential cross sections are compared to four theoretical models, based either on hadronic or on partonic degrees of freedom. The four models can describe the gross features of the data reasonably well, but differ strongly in their ingredients. In particular, the model based on Generalized Parton Distributions (GPDs) contain the interesting potential to experimentally access transversity GPDs.
Highlights
One of the major challenges in contemporary nuclear physics is the study of the transition between hadronic and partonic pictures of the strong interaction
One can vary the virtuality of the incoming photon Q2 = −(pe − pe)2, which effectively represents the transverse size of the probe, or the momentum transfer to the nucleon t =2, which effectively represents the transverse size of the target
The error bars on all cross sections include both statistical and systematic uncertainties added in quadrature
Summary
One of the major challenges in contemporary nuclear physics is the study of the transition between hadronic and partonic pictures of the strong interaction. At larger distances on the order of one Fermi, effective theories that take hadrons as elementary particles whose interactions are described by the exchange of mesons appear more applicable. The connection between these two domains is not well understood. In this figure, we keep, quite arbitrarily, only the experiments for which |t| > 3 GeV2 in photoproduction (SLAC [1, 2] and JLab [3]) and Q2 > 1.5 GeV2 in electroproduction
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