Search for exotic events at HERA


New physics at HERA could show up in the production of exotic high mass events with unusual signatures or also by deviations of the observed SM cross sections from the predictions. Our grous works on both aspects since several years. All analyses explore the region of highest Q2 .
            H1 has observed a few exotic events which are difficult to explain within the SM. There signature is:

One of the first events found (in '94) is shown below:

     Event with a high Pt muon and missing transverse momentum

 Within the standard model the only known process which leads to such a signature is W-production where the W decays into lepton and neutrino.
Indeed a fraction of the observed events are well compatible  with this expected process. There is however an excess  in cross section and some of the
events have kinematic properties which are very rare for W-production. The consistency with the SM prediction of the H1 observations is below 1%.
ZEUS has no excess in the electron and muon channels. They have however recently observed an exceess in the tau-channel.

                  A possible interpretation of theses events -apart from a still possible statistical fluctuation - could be top-production via flavour changing
neutral currents e.g.  u--> t  transitions. The analysis of this