Double-spin asymmetries for small-Q_T Drell-Yan pair production in transversely polarized p\bar{p} collisions

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  • 29 December 2007
Abstract
We discuss the Drell-Yan process at a measured transverse-momentum Q_T of the produced lepton pair in collisions of transversely polarized protons and antiprotons, to be observed at the proposed spin experiments at GSI. The large logarithmic contributions from multiple soft gluon emission, accompanying the Drell-Yan mechanism at small Q_T, are resummed to all orders in QCD perturbation theory up to next-to-leading logarithmic accuracy. Numerical evaluation of the cross sections shows that the resummation totally redistributes the Q_T spectrum of the lepton pair. We find that these effects of the soft gluon resummation to the polarized and unpolarized cross sections largely cancel in the corresponding spin asymmetry \aqt, although the important corrections remain, making \aqt almost constant in the small Q_T region. This constant behavior in turn allows us to use analytic saddle-point evaluation of the relevant resummation formula in the limit Q_T \to 0, not only to obtain quantitative estimate of \aqt, but also to clarify why the spin asymmetry in the p\bar{p} collisions at GSI is rather insensitive to the higher-order QCD corrections.

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