Eur. Phys. J. C (2007) 49: 967-971
https://doi.org/10.1140/epjc/s10052-006-0174-6

Regular Article - Theoretical Physics

The cos2φ asymmetry of Drell–Yan and J/ψ production in unpolarized pp̄ scattering

¹ Gruppo Collegato di Alessandria, Di.S.T.A., Universitá del Piemonte Orientale “A. Avogadro”, and INFN, 15100, Alessandria, Italy
² School of Physics, Peking University, Beijing, 100871, P.R. China
³ Departamento de Fisica, Universidad Técnica Federico Santa María, Casilla 110-V, Valparaíso, Chile

^* e-mail: barone@to.infn.it

Received: 25 July 2006
Revised: 31 October 2006
Published online: 19 December 2006

Abstract

We investigate the cos2φ azimuthal asymmetry in Drell–Yan and J/ψ production from unpolarized pp̄ scattering at GSI-HESR energies. The contribution to this asymmetry arising from the leading-twist Boer–Mulders function (x,k _T ²), which describes a correlation between the transverse momentum and the transverse spin of quarks in an unpolarized hadron, is explicitly evaluated, and predictions for the GSI-HESR kinematic regime are presented. We show that the cos2φ asymmetry is quite sizable both on the J/ψ peak and in the Drell–Yan continuum region. Therefore these processes may offer experimentally viable access to the Boer–Mulders function in the early unpolarized stage of GSI experiments.