Search for s channel single top quark production in pp collisions at sqrt(s) = 7 and 8 TeV

TL;DR

This paper reports a search for single top quark production in the s channel at the LHC using CMS data at 7 and 8 TeV, employing multivariate analysis to set limits on the production rate.

Contribution

It introduces a novel analysis using boosted decision trees to distinguish s-channel single top events from background in proton-proton collisions.

Findings

Measured cross sections: 7.1 +/- 8.1 pb at 7 TeV and 13.4 +/- 7.3 pb at 8 TeV

Signal significance of 2.5 standard deviations

Upper limit on production rate is 4.7 times the standard model expectation

Abstract

A search is presented for single top quark production in the s channel in proton-proton collisions with the CMS detector at the CERN LHC in decay modes of the top quark containing a muon or an electron in the final state. The signal is extracted through a maximum-likelihood fit to the distribution of a multivariate discriminant defined using boosted decision trees to separate the expected signal contribution from background processes. The analysis uses data collected at centre-of-mass energies of 7 and 8 TeV and corresponding to integrated luminosities of 5.1 and 19.7 inverse femtobarns, respectively. The measured cross sections of 7.1 +/- 8.1 pb (at 7 TeV) and 13.4 +/- 7.3 pb (at 8 TeV) result in a best fit value of 2.0 +/- 0.9 for the combined ratio of the measured and expected values. The signal significance is 2.5 standard deviations, and the upper limit on the rate relative to the standard model expectation is 4.7 at 95% confidence level.