Search for single top quarks in the tau+jets channel using 4.8 fb$^{-1}$ of $p\bar{p}$ collision data

TL;DR

This paper reports the first direct search for single top quark production in the tau+jets channel using 4.8 fb$^{-1}$ of data, employing multivariate techniques to discriminate signal from background and setting limits on the cross section.

Contribution

It introduces the first direct search for single top quarks in the tau+jets channel and combines results with other channels for improved sensitivity.

Findings

Observed data is consistent with background plus signal expectations.

Set an upper limit on the single top quark cross section at 95% C.L.

Achieved the most precise measurement of the combined cross section to date.

Abstract

We present the first direct search for single top quark production using tau leptons. The search is based on 4.8 fb$^{-1}$ of integrated luminosity collected in $p\bar{p}$ collisions at $\sqrt{s}$=1.96 TeV with the D0 detector at the Fermilab Tevatron Collider. We select events with a final state including an isolated tau lepton, missing transverse energy, two or three jets, one or two of them $b$ tagged. We use a multivariate technique to discriminate signal from background. The number of events observed in data in this final state is consistent with the signal plus background expectation. We set in the tau+jets channel an upper limit on the single top quark cross section of \TauLimObs pb at the 95% C.L. This measurement allows a gain of 4% in expected sensitivity for the observation of single top production when combining it with electron+jets and muon+jets channels already published by the D0 collaboration with 2.3 fb$^{-1}$ of data. We measure a combined cross section of $\SuperCombineXSall$ pb, which is the most precise measurement to date.