DVCS@JLab

Deeply Virtual Compton scattering in Hall A

E07-007 and E08-025 experiments

News: Our experiments will run during this upcoming fall 2010. For practical informations about the experiment, please consult our wiki. The shift signing page for the fall run is here.

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 dependence of the helicity dependent H(e,e'γ)p cross section at x_Bj=0.36 and Q² = 1.5, 1.9, and 2.3 GeV². The results are consistent with dominance of the leading twist ℑ[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).

E12-06-114 was approved by the JLab PAC30 in August, 2006. With a new calorimeter, the DVCS and deep virtual π⁰ measurements in x_Bj,Q² to (0.7,9.0 GeV²) will be extended. In PR07-007, approved by the JLab PAC31 in January, 2007, DVCS measurements at fixed Q², x_Bj and two different beam energies (6 and 4 GeV) are proposed. The kinematic structure of the ep→ epγ cross section will allow 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. Rosenbluth L/T separations of the ep→ epπ⁰ cross section, which is crucial to testing factorization in this channel will be obtained.