PURSUING INTERPRETATIONS OF THE HERA LARGE-Q(2) DATA

We explore interpretations of the anomaly observed by H1 and ZEUS at H ERA in deep-inelastic e(+)p scattering at very large Q(2), in terms of possible physics beyond the Standard Model. Since the present data co uld be compatible with either a continuum or a resonant solution, we d iscuss both the possibilities of new effective interactions and the pr oduction of a narrow state of mass M similar to 200 GeV with leptoquar k couplings. We compare these models with the measured Q(2) distributi ons: for the contact terms, constraints from LEP 2 and the Tevatron al low only a few choices of helicity and flavour structure that could ro ughly fit the HERA data. The data are instead quite consistent with th e Q(2) distribution expected from a leptoquark state. We study the pro duction cross sections of such a particle at the Tevatron and at HERA, the latter in the cases where it is produced from either a valence or a sea quark. The absence of a signal at the Tevatron disfavours the L ikelihood that any such leptoquark decays only into e(+)q. We then foc us on the possibility that the leptoquark is a squark with R-violating couplings. In view of the present experimental limits on such couplin gs, the most likely production channels are e(+)d --> (C) over tilde(L ) or perhaps e(+)d --> (t) over tilde, with e(+)s --> (t) over tilde a more marginal possibility. We point out that the (C) over tilde(L) co uld have competing branching ratios for R-conserving and R-violating d ecay channels, whereas (t) over tilde decays would be more likely to b e dominated by one or the other. Possible tests of our preferred model include the absence both of analogous events in e(-)p collisions and of charged current events, and the presence of detectable cascade deca ys whose kinematical signatures we discuss. This model could also make an observable contribution to K --> pi<(nu)over bar>nu and/or neutrin oless beta beta decay. We also discuss the possible implications for t he Tevatron and for e(+)e(-) --> (q) over bar q and neutralinos at LEP 2. (C) 1997 Elsevier Science B.V.