Polarisation transfer in proton Compton scattering at high momentum transfer

Hamilton, David Jonathan (2004) Polarisation transfer in proton Compton scattering at high momentum transfer. PhD thesis, University of Glasgow.

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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 (gamma,gamma'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'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 different 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 predictions. 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.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: High energy physics
Date of Award: 2004
Depositing User: Enlighten Team
Unique ID: glathesis:2004-74053
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 23 Sep 2019 15:33
Last Modified: 23 Sep 2019 15:33
URI: http://theses.gla.ac.uk/id/eprint/74053

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