Eur. Phys. J. A (2010) 45: 301-310
https://doi.org/10.1140/epja/i2010-11006-1

Regular Article - Theoretical Physics

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

¹ Dipartimento di Chimica e Fisica per l’Ingegneria e per i Materiali, Università di Brescia, I-25133, Brescia, Italy
² Istituto Nazionale di Fisica Nucleare, Sezione di Pavia, I-27100, Pavia, Italy

^* e-mail: bianconi@bs.infn.it

Received: 12 May 2010
Revised: 8 June 2010
Accepted: 18 June 2010
Published online: 30 July 2010

Abstract

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, q _T < 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 Monte Carlo generator where a standard cos(2) -asymmetry of the dilepton distribution is produced, thanks to a soft rescattering process between an active quark coming from a hadron and a spectator antidiquark coming from the other hadron. This produces cos(2) -asymmetries of the final hadron pair. Hadron and lepton asymmetries have the same size.