The Drell-Yan process

The Drell-Yan process is an electromagnetic effect in which a quark and antiquark from a pair of interacting hadrons annihilate to give a lepton pair. A brief description of hadron structure and the parton model is given to provide a necessary background. Then the general features of lepton pair production are described and the Drell-Yan formalism is set up. Experimental techniques are described next; these are rather simple since it is only necessary to detect the leptons emitted from hadron interactions. Predictions and tests of the basic model show that, in general, it works well. The anomalous features are the overall cross-section level (high by a factor of 2) and the unexpectedly large mean transverse momenta. Quantum chromodynamics (QCD) offers the explanation of these anomalies, and measurements of dilepton production provide important quantitative tests of QCD. Such measurements have also been used to determine nucleon structure functions and, for the first time, meson structure functions.