Low thrust inclusive lepton events at PETRA

In a search for new quark flavors, an excess of low thrust hadronic events containing isolated muons has been found by MARK-J and JADE at c.m.s. energies greater than 46.3 GeV. Combining all four experiments at PETRA one finds 14 events with thrust less than 0.8 and the cosine of the angle between the muon direction and the thrust axis less than 0.7. The prediction based on lower energy measurements is 2.5 events. There is no satisfactory explanation for these unusual events. A corresponding signal has not been seen in hadronic events with electrons