Striking events with isolated charged leptons, large missing transverse
momentum and large transverse momentum of the hadronic final state (PTX) have
been observed at the electron proton collider HERA. In the full HERA-I data
sample corresponding to an integrated luminosity of about 130 invpb, the H1
experiment observes 10 events with isolated electrons or muons and with PTX >25
GeV. Only 2.9 pm 0.4 events are expected from Standard Model (SM) processes.
Six of these events have PTX >40 GeV, while 1.1 pm 0.2 events are expected. The
ZEUS experiment observes good agreement with the SM. However, in a preliminary
search ZEUS has found two events with a similar event topology, but tau-leptons
instead of electrons or muons in the final state . Only 0.12 pm 0.02 events are
expected from SM processes.
Moreover, six events with two or more electrons forming an invariant mass
bigger than 100 GeV have been observed by the H1 experiment. Three events have
two electrons and three events have three electrons, while only 0.25 events are
expected in each case. The ZEUS measurement is in agreement with the SM
expectation.Comment: talk given at 38th Recontres de Moriond Electroweak Interactions and
Unified Theories, Les Arc (France) 200