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Double longitudinal spin asymmetries in single hadron photoproduction at high p_T at COMPASS

Abstract : This thesis presents a new study aiming at constraining the gluon contribution {\Delta G} to the 1/2 nucleon spin. The collinear pQCD theoretical framework, on which it is based, deals with asymmetries calculated from cross-sections for single inclusive hadron in the regime of quasi-real photoproduction {Q^2 < 1 GeV^2} at high hadron transverse momentum {p_T > 1 GeV/c). These calculations are done up to Next-to-Leading order with a foreseen inclusion of Next-to-Leading logarithm threshold gluon resummation, only performed for the unpolarised cross-sections yet. This makes the asymmetries sensitive to the gluon polarisation not only through Photon Gluon Fusion {\gamma* g} but also through resolved {\gamma*}g processes such as qg or gg. The measurement of the asymmetries is performed for all the COMPASS data available from 2002 to 2011 with a polarised muon beam at 160-200 GeV scattered off a longitudinally polarised target of deuteron ( {_6LiD} for 2002-2006) or proton ({NH_3} for 2007 and 2011). The asymmetries are presented in bins of pT and of pseudorapidity {\eta_h(p_T \in[1,4]} with {\langlep_T^2\rangle = 3 (GeV/c)^2}, and {\eta_h \in [-0.1, 2.4]}. Since the resummation calculations are not completed yet for the polarised case, the measurements are only compared with theoretical calculations using different parameterisation sets of polarised Parton Distribution Functions with a large range of different {\Delta G}. This comparison is then used to evaluate the {\Delta G} of these measurements. Complementary to this analysis, a study of new tracking detectors, the pixelised Micromegas, is performed. After calibration, it shows promising efficiencies and time and spatial resolutions.
Keywords : Hadrons
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Contributor : Valerie Poyeton <>
Submitted on : Tuesday, December 8, 2015 - 4:51:04 PM
Last modification on : Monday, February 10, 2020 - 6:12:41 PM
Long-term archiving on: : Saturday, April 29, 2017 - 7:53:05 AM


  • HAL Id : tel-01237393, version 1



Maxime Levillain. Double longitudinal spin asymmetries in single hadron photoproduction at high p_T at COMPASS. Nuclear Experiment [nucl-ex]. Université Paris saclay, 2015. English. ⟨tel-01237393⟩



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