Single W and Anomalous Single Top Production at HERA

TL;DR

This paper reports a comprehensive search for isolated leptons, W production, and anomalous single top production at HERA, finding results consistent with the Standard Model and setting limits on new physics scenarios.

Contribution

It provides the first combined analysis of H1 and ZEUS data on isolated leptons and sets new upper bounds on anomalous top quark production at HERA.

Findings

Observed events are consistent with SM predictions.

Measured W production cross sections agree with SM.

Set upper limit on anomalous top production cross section.

Abstract

The search for events containing isolated leptons (electrons or muons) and missing transverse momentum produced in e^{\pm}p collisions is performed individually and in a common phase space with the H1 and ZEUS detectors at HERA in the period 1994--2007. The presented H1+ZEUS data sample corresponds to an integrated luminosity of 0.97 fb^{-1}, and comprises the complete high energy data from the HERA programme. A total of 87 events are observed in the data, compared to a Standard Model prediction of 92.7 \pm 11.2. At large hadronic transverse momentum P_{T}^{X} > 25 GeV in the e^{+}p data, luminosity 0.58 fb^{-1}, 23 data events are observed compared to a SM prediction of 14.6 \pm 1.9. Production cross section measurements of events containing isolated leptons and missing transverse momentum and of single W production are performed by H1, where the measured cross sections are found to be in agreement with SM predictions. A complementary search by H1 for events containing an isolated tau lepton and missing P_{T} is also presented. A measurement of the W polarisation fractions is performed by H1, where the presented results are found to be in agreement with the SM. Finally, the H1 isolated lepton events are examined in the context of a search for anomalous single top production. In the absence of a clear signal, an upper limit on the anomalous top production cross section \sigma_{ep\to etX} < 0.16 pb is established at the 95% confidence level, corresponding to a limit an upper bound on the anomalous magnetic coupling \kappa_{tu\gamma} < 0.14.