Determination of the gluon polarization at RHIC and COMPASS
DSM/DAPNIA/SPhN, CEA-Saclay, Orme des merisiers, 91191, Gif-sur-Yvette, France
* e-mail: email@example.com
Accepted: 18 March 2007
Published online: 6 July 2007
The most recent determinations of the gluon polarization in the nucleon, , obtained at RHIC and COMPASS experiments, are reviewed. The former accesses the gluon polarization mainly through the production of neutral pions (PHENIX) or jets (STAR) in polarized proton collisions. The latter uses the photon-gluon fusion in polarized lepton-nucleon scattering, tagged either by open charm or high-pT hadrons production. All the results are in good agreement, and favour values of ΔG roughly between 0 and 0.5 at a few (GeV/c)2 , thus in contradiction with what could be derived from the Ellis-Jaffe sum rule and the axial anomaly. Much stronger constraints will be obtained in a near future by both programs, helping us to clarify the role of gluons in the nucleon spin.
PACS: 13.60.Hb Total and inclusive cross sections (including deep-inelastic processes) – / 13.88.+e Polarization in interactions and scattering – / 14.20.Dh Protons and neutrons – / 21.10.Hw Spin, parity, and isobaric spin –
© Società Italiana di Fisica and Springer-Verlag, 2007