Accompanied dileptons as a probe of an effective quark-lepton contact interaction at e+e− colliders

Abstract An effective quark-lepton contact interaction, possibly a low-energy remnant of deeply virtual heavy exotic exchanges, gives rise to characteristic spherical events in e + e − collisions, with an unlike-sign dilepton pair accompanied by distant jet activity and no missing energy, due to e + e − → / + / − + q q . The helicity amplitudes for this process, where the new hypothetical interaction interferes with the standard γ + Z 0 exchanges are calculated by spinor-product techniques. The system of leptons and jets produced does not exhibit any particular structures, as would be the case with similar events due to Higgs particles, leptoquarks or extra neutral currents. Our accompanied dilepton signal events are separable by appropriate cuts from a background due to heavy-quark production and their angular distribution is flatter than expected from the standard γ + Z 0 contributions.