Deeply virtual compton scattering off longitudinally polarised protons at HERMES

QC Physics

Mahon, David Francis ; Kaiser, Ralf

University:University of Glasgow

Department:School of Physics and Astronomy

关键词: Deeply virtual Compton scattering, Generalised parton distributions, nucleon structure, lepton nucleon scattering;   

Others  :  http://theses.gla.ac.uk/1924/1/2010mahonphd.pdf

来源: University of Glasgow

【 摘 要 】

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 modelswhich aim to provide a better understanding of GPDs.