IFT 94/23 TESTING THE WWγ COUPLING AT e + e − COLLIDERS ∗

The production of single photons plus missing energy at future ee colliders can provide a testing ground for non-standard WWγ couplings. We show that even with conservative estimates of systematic errors there is still considerable sensitivity to anomalous couplings. In spite of many experimental successes certain aspects of the standard model still await for direct tests. Among them is the non-abelian sector of the model and, in fact, a detailed investigation of gauge boson self-couplings will constitue one of the primary physics goals of the next linear colliders. The processes with production of gauge bosons in the final state at future colliders should provide such crucial tests of electroweak theory. In particular, they should allow to improve LEP bounds on non-Yang-Mills like triple gauge boson vertices. In this talk we suggest that the process ee → ννγ containing a single isolated photon and missing energy may be used to study the precise structure of the WWγ vertex. Such final states have been studied at PETRA and at LEP as a means of determining the number of light neutrini. At these energies though, not much sensitivity to anomalous WWγ form-factors should be expected, as s-channel processes mediated by virtual Z exchange also play an important role. However, at Next Linear Collider (NLC) energies ( √ s = 500 GeV), s channel contributions become less important and the bulk of the cross-section comes from t channel W exchange. The process ee → ννγ from the point of view ofWWγ studies has been considered earlier. The novel feature of our analysis, as we will show, is that it is possible to choose cuts which enhance the sensitivity of the observed cross-sections and differential distributions to the WWγ form-factor. The advantage of the process ee → ννγ over the most studied reaction ee → WW is that the latter, in spite of being a sensitive probe of non-standard WWγ and WWZ couplings, suffers from the drawback that there is no obvious way to disentangle the effects of WWγ and WWZ form-factors. Hence it is desirable to investigate other channels where such γ − Z interference effects are not present. The deviations of non-abelian vertices from the standard model couplings, as was shown by Hagiwara et al., can be parametrized by seven possible Lorentz and Presented at the Joint US-Polish Workshop ”Physics from Planck Scale to Electroweak Scale”, Warsaw, September 21-24, 1994 Supported in part by the Polish Committee for Scientific Research Grant 2 P302 095 05