Nucleon Electro-Weak Structure (NEWS) studies at Ohio University

DVCS in Hall A @ JLab

New QCD factorization theorems establish that exclusive reactions such as H(e,e'γ)p and H(e,e'π0)p, in the deeply virtual limit of large Q2, W, and -t< Q2 are determined (in leading twist, or leading term in an expansion in inverse powers of Q2) by a new class of quark and gluon matrix elements, called Generalized Parton Distributions (GPDs). The GPDs correlate the transverse spatial distribution of the struck parton (quark or gluon) with the light-cone momentum fraction of the parton in the target.

Hall A experiment E00-110 measured the Q2 dependence of the helicity dependent H(e,e'γ)p cross section at xBj=0.36 and Q2 = 1.5, 1.9, and 2.3 GeV2. The results are consistent with dominance of the leading twist Im[BH*DVCS] term. The experiment also measured the helicity independent cross section at Q2 = 2.3 GeV2. The latter results show evidence for strong contributions from both the Real part of the BH*DVCS interference and the pure |DVCS|2 terms (as well as the |BH|2 term).


The expansion of the existing calorimeter is required for a new series of DVCS experiments at 6 and 12 GeV. The Hall A 12 GeV DVCS experiment, E12-06-114 was approved by PAC30 in August, 2006 (J.Roche, C.E. Hyde-Wright, co-spokespersons). With the new calorimeter, we will extend DVCS and deep virtual π0 measurements in xBj,Q2) to (0.7,9.0 GeV2). In E07-007, we propose DVCS measurements at fixed Q2, xBj and two different beam energies (6 and 4 GeV). The kinematic structure of the ep\rightarrow epγ cross section will allow us to separate the Real part of the BH*DVCS interference from the pure |DVCS|2 term at all three Q2 values of the previous E00-110. We will also obtain Rosenbluth L/T separations of the $ep\rightarrow epπ0 cross section, which is crucial to testing factorization in this channel.


DVCS-GPD articles