W-D. Nowak - INFN
W-D. Nowak - INFN
W-D. Nowak - INFN
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Wolf-Dieter <strong>Nowak</strong>, Perspectives in Hadronic Physics, May 15, 2008 – p. 8<br />
Determination of Gluon Contribution to Nucleon Spin<br />
High-p t hadron pairs or single hadrons quasi-real photoprod.: 〈Q 2 〉 ≈ 0.1 GeV 2<br />
Sensitivity through γ ∗ g ‘direct’ hard scattering or ‘resolved-photon’ process<br />
left graphs: direct processes; right graphs: resolved-photon processes [COMPASS analysis]<br />
PGF<br />
R<br />
Extraction heavily relies on<br />
PYTHIA simulation (LO only !)<br />
0.3<br />
0.2<br />
0.1<br />
0<br />
QCDC<br />
*<br />
γ<br />
g→qq<br />
*<br />
γ<br />
q→qg<br />
*<br />
γ<br />
q→q<br />
Leading<br />
qq’→qq’<br />
qg→qg<br />
gg→gg<br />
low p<br />
T<br />
Processes:<br />
Hard scale µ 2 ≃ 3 GeV 2<br />
only ‘loosely’ correlated<br />
with x g (〈x g 〉 ≃ 0.1)<br />
COMPASS: Open-charm production (γ ∗ g → c¯c) and hadron pairs<br />
HERMES: Single high-p t hadrons. Pairs in old analysis (all Q 2 , 〈x g 〉 ≃ 0.17<br />
[PRL84 (2000) 2584] ∆g<br />
g = 0.41 ± 0.18 stat ± 0.03 sys−exp (±unknown sys−Model )<br />
RHIC: A LL in inclusive direct γ & π 0 production, inclusive jet production
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