Initial State Helicity Correlation in Wide Angle Compton Scattering

D Nikolenko, I Rachek, Yu Shestakov, GB Franklin, V Mamyan, B Quinn, T Averett, M Cummings, C Perdrisat, H Yao, Guy Ron

Research output: Other contribution


We propose1 an experiment to measure the initial state helicity correlation asymmetry ALL in Real Compton Scattering (RCS) by scattering longitudinally polarized
photons from a longitudinally polarized proton target at the invariant s= 8 (GeV/c)
three scattering angles, θ
γ = 60◦
, 90◦ and 136◦
. This experiment could potentially
run with the b1 experiment (PR12-13-011) to make use of the very similar target setup
already in place.
Two JLab RCS experiments, E99-114 and E07-002, demonstrated the feasibility
of the experimental technique. The experiment utilizes an untagged bremsstrahlung
photon beam and the UVA/JLAB polarized target. The scattered photon is detected
in the future NPS. The coincident recoil proton is detected in the Hall C magnetic
spectrometer HMS.
The applicability of QCD, in the moderate energy range, to exclusive reactions is
a subject of great interest and any opportunity to test unambiguously its prediction
should be taken.
Calculations by G. A. Miller in a constituent quark model reproduced the KLL experimental result but revealed a large disagreement with the GPD prediction for ALL .
It is but one of the goals of our proposal to test this prediction which could force a
modification of our understanding of the high-t photo-induced processes such as RCS,
pion photoproduction, and deuteron photo–disintegration. A measure of ALL and the
conclusions that can be drawn from the results would give insight into understanding
quark orbital angular momentum in the proton.
We request 742 hours of 90 nA at 4.4 GeV electron beam to measure the polarization observable ALL to a statistical accuracy better than 0.09. This measurement
will significantly increase our experimental confidence in the application of the GPD
approach to reactions induced by real photons which will play a major role in nucleon
structure physics at JLab.
Original languageAmerican English
TypeA Proposal to Jefferson Lab PAC 42
Media of outputJefferson Lab PAC 42
Number of pages62
StatePublished - 2 Jun 2014


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