Abstract

A search for single top production (e+e−→tc̄) via flavour changing neutral currents (FCNC) was performed using the data taken by the DELPHI detector at LEP2. The data analyzed have been accumulated at center-of-mass energies ranging from 189 to 208 GeV. Limits at 95% confidence level were obtained on the anomalous coupling parameters κγ and κZ.

Highlights

  • Flavour changing neutral currents (FCNC) are highly suppressed in the Standard Model (SM) due to the Glashow–Iliopoulos–Maiani (GIM) mechanism [1]

  • Luminosity collected by DELPHI and used in this analysis for each center-of-mass energy

  • The number of data events and expected background from the SM processes passing the likelihood ratio selection are shown in Table 2 for all center-of-mass energies, together with the signal efficiencies convoluted with the W hadronic branching ratio

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Summary

Introduction

Flavour changing neutral currents (FCNC) are highly suppressed in the Standard Model (SM) due to the Glashow–Iliopoulos–Maiani (GIM) mechanism [1]. In the approach which gives the most conservative limits on the couplings, the interference term, which depends on gi and zi , gives a negative contribution to the cross-section of the process e+e− → tc. This corresponds to the requirement [6]: g1z1 + g2z2 = −1. The existence of anomalous top couplings to gauge bosons allows the top to decay through t → cγ and t → cZ in addition to the dominant decay mode t → bW This effect was taken into account in the evaluation of results. Luminosity collected by DELPHI and used in this analysis for each center-of-mass energy (see text for details)

The DELPHI data and simulated samples
Hadronic channel
Semileptonic channel
Systematic errors and limit derivation
Findings
Summary

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