Massive lepton pair production in hadronic interactions and the quark model

Abstract

The experimental data on the production of μ +μ − and e + e − pairs in hadronic interactions are reviewed. The region above ∼ 3 GeV in lepton pair mass is considered, with continuum and resonance contributions being dealt with separately. The continuum is compared critically with the predictions of the naive Drell-Yan model of q q annihilation, and its limitations are discussed. To the extent that the simple model is applicable, quark distributions in hadrons can be extracted; these supplement information from other sources. Embellishments to the simplest Drell-Yan picture, and their degree of success in explaining the data, are considered. Higher order QCD processes may be the dominant mechanism, especially at large transverse momentum. Resonance production (of the ψ and γ families) differs from the continuum. Various mechanisms, differing at the level of which partons contribute, have been proposed. None of these on its own seems adequate, but a picture of what sort of mixture is required is emerging. The aim for the future is to check in more detail the higher order corrections to the Drell-Yan process for the continuum, and to test more stringently whether a mechanism involving subprocesses whose relative magnitudes are derived theoretically really does describe well all aspects of resonance production. This may then enable us to use lepton pair data to probe in greater detail the parton structure of hadrons, and to understand better the relevance of higher order QCD phenomena to hard scattering processes.