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.

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: https://theses.gla.ac.uk/id/eprint/74053