Measuring the WWγ vertex in single W production at ep colliders

Abstract A detailed analysis of single W production in ep collisions via ep→eW ± X is presented by using helicity amplitudes for general WWγ couplings. Analytic expressions are given for the γ q→W ± q′ helicity amplitudes which describe ep→eWX in the Weizsacker-Williams approximation and provide a semiquantitative understanding of the results obtained with the full matrix elements. Possibilities to test the gauge theory structure of the WWγ vertex at HERA (√ s =314 GeV) and at an ep collider in the LEP tunnel (√ s ≈1.4 TeV) are explored. It is found that at HERA the WWγ vertex can be measured with 30–50% accuracy after a few years of running.