Observation of events at very high Q2 in ep collisions at HERA

Measurements of ep scattering with squared 4—momentum transfer Q2 up to 35000 GeV2 are compared with the expectation of the standard deep-inelastic model of lepton—nucleon scattering (DIS). For Q2 > 15000 GeV2, Nobs = 12 neutral current candidate events are observed where the expectation is NDIS = 4.71 ± 0.76 events. In the same Q2 range, Nobs = 4 charged current candidates are observed where the expectation is NDIS = 1.77 ± 0.87 events. The probability P(N ≥ Nobs) that the DIS model signal N fluctuates to N ≥ Nobs in a random set of experiments is 6 × 10−3 for neutral current and 0.14 for charged current. The difference in the observed and expected number of Neutral Current events is mostly due to events at large masses $$M = \sqrt {xs}$$ in which the positron is backscattered at large y = Q2/M2.