Isolated Leptons and Single Top at HERA

The search for events containing isolated leptons and missing transverse momentum produced in ep collisions is performed individually and in a common phase space with the H1 and ZEUS detectors at HERA. The combined H1 and ZEUS data sample corresponds to an integrated luminosity of 0.98 fb^-1 and comprises the complete high energy data from the HERA programme. A total of 81 events are observed in the data, compared to a Standard Model prediction of 87.8 \pm 11.0, which is dominated by single W production. At large hadronic transverse momentum P_T^X > 25 GeV in the e+p data, integrated luminosity 0.58 fb^-1, 23 data events are observed compared to a SM prediction of 14.0 \pm 1.9. The total single W production cross section is measured as 1.06 \pm 0.16 (stat.) \pm 0.07 (sys.) in agreement with a SM expectation of 1.26 \pm 0.19. The isolated lepton events are examined in the context of a search for anomalous single top production, where the hadronic decays of the W are additionally considered. Although several top-like candidates are present in the H1 data no clear signal is observed and an upper limit on the anomalous single top production cross section of < 0.25 pb is established at the 95% confidence level. This limit corresponds to an upper bound on the anomalous magnetic coupling of < 0.18 assuming a top mass of 175 GeV.

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