Deeply Virtual Compton scattering in Hall A
E07-007 and E08-025 experimentsNews: 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 xBj=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 xBj,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, xBj 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.
Last update: July 8, 2010.