Search for single top quark production in pbar p collisions at sqrt{s}=1.96 TeV in the missing transverse energy plus jets topology

TL;DR

This paper reports a search for single top quark production in proton-antiproton collisions at 1.96 TeV, using the CDF II detector, and finds an excess consistent with the standard model prediction.

Contribution

It introduces a novel analysis method using neural networks and b-jet identification to detect single top quark production in a challenging missing energy plus jets topology.

Findings

Observed an excess of events consistent with single top production

Measured cross section of 4.9 pb with uncertainties

Results agree with standard model predictions

Abstract

We report a search for single top quark production with the CDF II detector using 2.1 fb-1 of integrated luminosity of pbar p collisions at sqrt{s}=1.96 TeV. The data selected consist of events characterized by large energy imbalance in the transverse plane and hadronic jets, and no identified electrons and muons, so the sample is enriched in W -> tau nu decays. In order to suppress backgrounds, additional kinematic and topological requirements are imposed through a neural network, and at least one of the jets must be identified as a b-quark jet. We measure an excess of signal-like events in agreement with the standard model prediction, but inconsistent with a model without single top quark production by 2.1 standard deviations (sigma), with a median expected sensitivity of 1.4 sigma. Assuming a top quark mass of 175 GeV/c2 and ascribing the excess to single top quark production, the cross section is measured to be 4.9+2.5-2.2(stat+syst)pb, consistent with measurements performed in independent datasets and with the standard model prediction.