Deeply Virtual Exclusive Reactions with CLAS

Abstract

Deeply virtual exclusive reactions offer a unique opportunity to study the structure of the nucleon at the parton level as one has access to Bjorken x B and momentum transfer to the nucleon t at the same time. Such processes can reveal much more information about the structure of the nucleon than either inclusive electroproduction or elastic form factors alone. Dedicated experiments to study Deeply Virtual Compton Scattering (DVCS) and Deeply Virtual Meson Production (DVMP) have been carried out in Hall B at Jefferson Lab. DVCS helicity–dependent and helicity–independent cross sections and beam spin asymmetries have been measured with CLAS, as well as cross sections and asymmetries for the π 0 , η, ρ 0 , ρ + , ω and ϕ for exclusive electroproduction. The data were taken in a wide kinematic range in Q 2 = 1 − 4.5 GeV 2 , x B = 0.1 − 0.5 , and | t | up to 2 GeV2. We will discuss the interpretation of these data in terms of traditional Regge and Generalized Parton Distributions (GPDs) models. The successful description of the recent CLAS pseudoscalar meson exclusive production data by GPD-based model provides a unique opportunity to access the transversity GPDs. We view the work presented in this report as leading into the program of the Jefferson Lab 12 GeV upgrade. The increased energy and luminosity will allow us to acquire data at much higher Q 2 and x B , and perform Rosenbluth L/T separations of the cross sections.