Azimuthal asymmetries in exclusive four-particle “Drell-Yan” events

I study hard collisions between unpolarized protons and antiprotons where a lepton-antilepton pair is detected in coincidence with a final proton-antiproton pair, and no more particles are produced, in the regime 10 GeV2 ≪ s ≪ 1000 GeV2 , M > 4 GeV, qT < 3 GeV/c. The present work is centered on azimuthal asymmetries. Because of momentum conservation, a Boer-Mulders term in the momentum distribution of a quark implies a balancing effect in the momentum distribution of some spectators. This produces azimuthal asymmetries of the final hadrons. To analyze this, I have organized a parton-level MonteCarlo generator where a standard cos(2φ)-asymmetry of the dilepton distribution is produced, thanks to a soft rescattering process between an active quark coming from a hadron and a spectator anti-diquark coming from the other hadron. This produces cos(2φ)-asymmetries of the final hadron pair. Hadron and lepton asymmetries have the same size.