Deeply virtual compton scattering off longitudinally polarised protons at HERMES

Mahon, David Francis (2010) Deeply virtual compton scattering off longitudinally polarised protons at HERMES. PhD thesis, University of Glasgow.

Abstract

This thesis details the simultaneous extraction of three polarisation-dependent asymmetries in the distribution of real photons from the e p → e p γ interaction and its indistisguishable deeply virtual Compton scattering and Bethe-Heitler processes at the HERMES fixed-target experiment at Desy. The data analysed were taken using a longitudinally polarised 27.57 GeV positron beam incident on a longitudinally polarised hydrogen gas target. The extracted asymmetries include two single-spin asymmetries A_UL and A_LU which depend on the polarisation of the target and beam respectively, averaged over all other polarisation states. The double-spin asymmetry A_LL dependent on the product of the beam and target polarisations is extracted for the first time.
The asymmetry amplitudes extracted relate to combinations of Generalised Parton Distributions (GPDs), predominantly H and Htilde. The extracted amplitudes will be presented across the HERMES kinematic range alongside theoretical predictions from a GPD model based on double distributions.
Large sin phi and cos(0phi) amplitudes are observed for A_UL and A_LL respectively, with an unexpectedly large sin(2phi) amplitude for A_UL . The results for the A_UL and A_LL asymmetries are broadly compatible with theory predictions, and the extracted A_LU amplitudes are compatible with HERMES results extracted from a significantly larger data set.
It is foreseen that these results will form input to future global data-based GPD models
which aim to provide a better understanding of GPDs.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Deeply virtual Compton scattering, Generalised parton distributions, nucleon structure, lepton nucleon scattering
• Subjects: Q Science > QC Physics
• Colleges/Schools: College of Science and Engineering > School of Physics and Astronomy
• Supervisor's Name: Kaiser, Prof. Ralf
• Date of Award: 2010
• Depositing User: Mr David F Mahon
• Unique ID: glathesis:2010-1924
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 22 Jun 2010
• Last Modified: 10 Dec 2012 13:48
• URI: https://theses.gla.ac.uk/id/eprint/1924