arXiv:hep-ph/0310197·v2·High Energy Physics — Phenomenology
QCD Hard Scattering and the Sign of the Spin Asymmetry A_LL^pi
Barbara Jager🇩🇪 · Stefan Kretzer🇺🇸 · Marco Stratmann🇩🇪 · Werner Vogelsang🇺🇸
Abstract
Recent preliminary PHENIX data are consistent with a negative and sizable longitudinal double-spin asymmetry A_LL^pi for pi^0 production at moderate transverse momentum p_perp \simeq 1 - 4 GeV and central rapidity. By means of a systematic investigation of the relevant degrees of freedom we show that the perturbative QCD framework at leading power in p_perp produces at best a very small negative asymmetry in this kinematic range.
Comments: 4 pages, 3 figures, final version published in PRL (only minor changes; note: title changed in published version)