Abstract

A search for single-top production, ep→etX, has been performed with the ZEUS detector at HERA using data corresponding to an integrated luminosity of 0.37 fb−1. No evidence for top production was found, consistent with the expectation from the Standard Model. Limits were computed for single-top production via flavour changing neutral current transitions involving a neutral electroweak vector boson, γ or Z. The result was combined with a previous ZEUS result yielding a total luminosity of 0.50 fb−1. A 95% credibility level upper limit of 0.13 pb was obtained for the cross section at the centre-of-mass energy of s=315 GeV.

Highlights

  • IntroductionPolicy Office. Supported by the Spanish Ministry of Education and Science through funds provided by CICYT. Supported by the Natural Sciences and Engineering Research Council of Canada (NSERC). Partially Supported by the German Federal Ministry for Education and Research (BMBF). Supported by RF Presidential grant N 4142.2010.2 for Leading Scientific Schools, by the Russian Ministry of Education and Science through its grant for Scientific

  • Technology (MEXT) and its grants for Scientific Research. Supported by the Korean Ministry of Education and Korea Science and Engineering Foundation. Supported by FNRS and its associated funds (IISN and FRIA) and by an Inter-University Attraction Poles Programme subsidised by the Belgian Federal SciencePolicy Office. Supported by the Spanish Ministry of Education and Science through funds provided by CICYT. Supported by the Natural Sciences and Engineering Research Council of Canada (NSERC). Partially Supported by the German Federal Ministry for Education and Research (BMBF). Supported by RF Presidential grant N 4142.2010.2 for Leading Scientific Schools, by the Russian Ministry of Education and Science through its grant for ScientificResearch on High Energy Physics and under contract No 02.740.11.0244

  • The present analysis extends the previously published ZEUS results [14] which used data from the HERA I running period,62 corresponding to a total integrated luminosity of 0.13 fb−1

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Summary

Introduction

Policy Office. Supported by the Spanish Ministry of Education and Science through funds provided by CICYT. Supported by the Natural Sciences and Engineering Research Council of Canada (NSERC). Partially Supported by the German Federal Ministry for Education and Research (BMBF). Supported by RF Presidential grant N 4142.2010.2 for Leading Scientific Schools, by the Russian Ministry of Education and Science through its grant for Scientific. Funded by Max Planck Institute for Physics, Munich, Germany. Senior Alexander von Humboldt Research Fellow at Hamburg University, Institute of Experimental Physics, Hamburg, Germany. 23 at Cracow University of Technology, Faculty of Physics, Mathemathics and Applied Computer Science, Poland. At Department of Physics, University of Bonn, Germany. The couplings tu V and tcV were investigated in e+e− interactions at LEP2 by searching for single-top production through the reactions e+e− → tu (+c.c.) and e+e− → tc (+c.c.) [10,11]. The same FCNC couplings could induce single-top production in ep collisions, ep → et X [12], in which the incoming lepton exchanges a γ or Z with an up quark in the proton, yielding a top quark in the final state, see Fig. 1. At Max Planck Institute for Physics, Munich, Germany, External Scientific Member. A combination of the results from the two running periods (total integrated luminosity 0.50 fb−1) has been performed

Theoretical framework
Experimental setup
Monte Carlo simulation
Event selection
Online selection
Offline selection
Selection of single-top candidates
Systematic uncertainties
Limits on FCNC
Limits on the cross section and κγ
Limits on the top anomalous branching ratios
Findings
Conclusions

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