Extraction of Polarised Quark Distributions of the Nucleon from Deep Inelastic Scattering at the HERMES Experiment

This thesis reports on the measurement of polarised quark <br>distributions of the nucleon from deep inelastic polarised <br>positron-proton scattering in the HERMES experiment at DESY. <br> <br>The first part of this thesis describes the achievement and <br>measurement of longitudinal positron polarisation in the HERA <br>storage ring, using Compton scattering of polarised laser light. <br>Emphasis is laid on the setup and performance of the laser <br>optical system of the so-called 'Longitudinal Polarimeter'. <br> <br>In the second part of this thesis, polarised quark distributions <br>for up-, down-, and sea-quarks are extracted from the analysis <br>of semi inclusive cross section asymmetries in deep inelastic <br>scattering. The data cover a kinematic range of <br>0.023 < x < 0.6 and 1.0 GeV^2 < Q^2 < 10 GeV^2. Polarised quark <br>distributions are extracted as a function of Bjorken-x for the <br>up-, down-, and sea-flavours, as well as for the valence up-, <br>valence down-, and sea-flavours. The polarisation of the <br>up-quarks was determined to be positive in the entire kinematic <br>range and increases up to a value of approximately 0.5 for large <br>values of x. Similarly, the down-quarks show negative polarisation, <br>whereas the sea-quarks carry no significant polarisation in the <br>measured range. Furthermore, the first and second moments of the <br>extracted polarised quark distributions are determined and <br>compared to existing analyses of world data on inclusive <br>polarised deep inelastic scattering and to QCD lattice <br>calculations. The extracted moments are consistent with the <br>analyses of the inclusive scattering data assuming SU(3) flavour <br>symmetry for the polarised quark distributions in the nucleon, <br>whereas there is a clear discrepancy to the results of the <br>lattice QCD calculations.

Author dc:creator

• Beckmann, Marc

Contributors dc:contributor

• Königsmann, Kay

• polarisierte Quarkdichteverteilungen
• polarisierte Lepton-Nukleon-Streuung
• deep inelastic scattering
• polarised quark distribution
• nucleon

Repository record source_url

https://freidok.uni-freiburg.de/data/77

OAI identifier oai:identifier

oai:freidok.uni-freiburg.de:77