Measuring the WWγ vertex in the process ep→γνX

We present a detailed analysis of the process ep→γνX as a means of studying the gauge structure of the WWγ vertex. We find that the differential cross section of high pT photons offers a sensitive measure of anomalous WWγ couplings. At HERA (√s=314 GeV), after several years of running, the WWγ vertex can be measured to δKγ≅-2.0+2.9 and δλγ≅-2.5+3.0 (95% C.L.) which offers an improvement over existing constraints from direct measurements using associated Wγ production in anti pp collisions but is less sensitive than the competing process at HERA, ep→eWX. For a higher energy ep collider, LEP-LHC (√s=1.3 TeV), the WWγ vertex can be measured to δKγ≅±0.4 and δλγ≅±0.1 at 95% C.L. which is more sensitive to λγ than the process e+e-→W+W- at the LEP200 e+e- collider and is comparable to the LEP200 sensitivity to κγ. These values are also roughly comparable to the competing process ep→eWX at LEPH-LHC and to what is expected from associated γW production at the LHC and SSC for κγ but they are about half as sensitive to λγ as the LHC and SSC. (orig.)