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Title Polarisation Transfer in Proton Compton Scattering at High Momentum Transfer
Authors David Hamilton
JLAB number JLAB-PHY-04-330
LANL number (None)
Other number DOE/ER/40150-5046
Document Type(s) (Thesis) 
Supported by U.S. Naval Research: No
Supported by Jefferson Lab LDRD Funding: No
A PHD thesis
Advisor(s) :
(University of Glasgow)
Publication Abstract: The Jefferson Lab Hall A experiment E99-114 comprised a series of measurements to explore proton Compton scattering at high momentum transfer. For the first time, the polarisation transfer observables in the p (~ 0 ~ p) reaction were measured in the GeV energy range, where it is believed that quark-gluon degrees of freedom begin to dominate. The experiment utilised a circularly polarised photon beam incident on a liquid hydrogen target, with the scattered photon and recoil proton detected in a lead-glass calorimeter and a magnetic spectrometer, respectively. A high efficiency proton polarimeter located at the spectrometer focal plane was used to extract the beam helicity asymmetry, from which the polarisation transfer components (K LL and K LT ) at a centre-of-mass energy squared s = 6:9 GeV 2 and momentum transfer t = 4:0 GeV 2 were determined. This analysis involved modelling the precession of the proton spin in the magnetic optics of the spectrometer, as well as calibration of the polarimeter analysing power via the p (~e; e 0 ~p) reaction. The real power of this polarisation measurement lies in the fact that the two reaction mechanisms assumed to contribute in this kinematic domain - the leading twist pQCD approach and the handbag factorisation - give drastically di erent predictions for K LL at wide angles. The results, K LT = 0:111 0:078 (stat) 0:04 (syst) ; K LL = 0:677 0:083 (stat) 0:04 (syst), indicate unambiguous agreement with the handbag mechanism and disagreement with the pQCD pre- dictions. Furthermore, in terms of the non-perturbative structure of the proton the results highlight the importance of states with non-zero quark orbital angular momentum.
Experiment Numbers: other
Group: Hall A
Document: pdf
Accepted Manuscript:
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