A QCD calculation of the transverse momentum distribution of Drell-Yan pairs including soft emission and non-abelian effects

Abstract

The well-known Parisi and Petronzio LLA result for the QCD transverse momentum distribution of Drell-Yan pairs at p T⪡ Q takes into account the non-singlet contribution only and totally neglects non-abelian effects due to the singlet contribution. The latter becomes substantial and sometimes dominant at pp and pp collider energies, and thus any comparison with data from these machines will require computation of its effects. We present a QCD Monte Carlo procedure which allows one to calculate the transverse momentum distribution with both non-singlet and singlet contributions included. At the same time it computes the evolution of parton density functions and the correlations between transverse and longitudinal distributions. Phase-space effects are duly taken into account. It is found that, at collider energies, the singlet contribution completely alters QCD predictions for dimuon transverse momenta giving at times 〈 p T〉 ∼ 4 times larger than the non-singlet contribution. Quantitative results are presented and a comparison with existing data is made, showing satisfactory agreement with the experimentally observed behaviours.