Speaker
Prof.
Michel Guidal
(Orsay)
Description
A longstanding goal in nuclear and particle physics has been to describe the three dimensional structure of the nucleon in terms of the quarks and gluon fields. In this regard, exclusive electron scattering experiments, in which all final state particles are measured, are important contributors. Examples are electron elastic scattering, deeply virtual Compton scattering (DVCS), and deeply virtual meson electroproduction (DVMP). The latter includes pseudoscalar mesons with intrinsic spin and parity JP=0-, such as π-, π0, π+ and η, and vector mesons, which have the same spin and parity as the photon, JP=1-, such as ρ-, ρ0, ρ+, ω and φ. Exclusive electron scattering reactions at high momentum transfers directly related to Generalized Parton Distributions (GPDs) of quarks and gluons. Most reactions studied, such as DVCS or vector meson electroproduction, are primarily sensitive to the chiral-even GPDs. Very little is known about the chiral-odd GPDs, except that HT becomes the transversity function h1 in the forward limit. The chiral-odd GPDs are difficult to access since hard subprocesses with the quark spin-flip are suppressed. It turns out that pseudoscalar meson electroproduction, and especially π0 and η production, were identified as especially sensitive to the parton helicity-flip subprocesses.
Dedicated experiments to study Deeply Virtual Meson Production have been carried out in Hall B at Jefferson Lab. The cross sections and asymmetries of the exclusive pseudoscalar meson electroproduction processes in a very wide kinematic range of Q2, xB and t have been measured with CLAS.
The comparison of these data with the theoretical models will help us to better understand the connection of these processes with the longitudinal and transverse 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 study these processes at much higher Q2 and xB and perform Rosenbluth L/T separations of the cross sections.
Primary author
Prof.
Michel Guidal
(Orsay)
