Leptoquark signal from global analysis

Data from HERA, LEP and the Tevatron as well as from low energy experiments are used to constrain the Yukawa couplings for scalar and vector leptoquarks in the Buchmüller–Rückl–Wyler effective model. In the limit of very high leptoquark masses constraints on the coupling to the mass ratio \(\lambda / M\) are derived using the contact-interaction approximation. For finite masses the coupling limits are studied as a function of the leptoquark mass. Some leptoquark models are found to describe the existing experimental data much better than the standard model. The increase in the global probability observed for models including \(S_1\) or \(\tilde{V}_{0}\) leptoquark production/exchange corresponds to an effect of more than \(3\sigma\). Assuming that a real leptoquark signal is observed, the allowed region in the \(\lambda\)–M plane is calculated. The leptoquark signal mostly results from the new data on the atomic parity violation in cesium, but is also supported by recent LEP2 measurements, unitarity violation in the CKM matrix and HERA high-\(Q^2\) results.