Search for s-channel single top-quark production in pp collisions at 8 TeV with the CMS experiment at the LHC

M Merola

doi:10.1016/j.nuclphysbps.2015.10.066

Abstract

A search for single top-quark production in the s channel in proton-proton collisions at a centre-of-mass energy of s=8 TeV by the CMS detector at the LHC is presented. Leptonic decay modes of the top quark with an electron or muon in the final state are considered. The signal is extracted by performing a maximum-likelihood fit to the distribution of a multivariate discriminant defined using Boosted Decision Trees to separate the expected signal contribution from the background processes. Data collected in 2012, corresponding to an integrated luminosity of 19.3/fb, lead to an upper limit on the cross section times branching ratio of 11.5 pb at 95% confidence level.

Highlights

The top quark, discovered at the Tevatron proton antiproton collider in 1995 [1, 2], can be produced via strong interaction in association with the top anti-quark and via electroweak interaction as single top
The single top production in the s channel at the LHC is unfavoured with respect to the other two production modes, involving a quark and an anti-quark in the initial state (Figure 1)
The SM prediction at NNLL order for this process at the LHC and at 8 TeV is σtsh−ch. = 5.55 ± 0.08(scale) ± 0.21(PDF) pb [3]. The interest in this channel is focused on possible enhancement of its production due to new physics involving non-SM mediators, like W or charged Higgs boson [4]

Summary

Introduction

The top quark, discovered at the Tevatron proton antiproton collider in 1995 [1, 2], can be produced via strong interaction in association with the top anti-quark and via electroweak interaction as single top. Three are the different single top production modes, the t channel, the s channel and the tW production. The single top production in the s channel at the LHC is unfavoured with respect to the other two production modes, involving a quark and an anti-quark in the initial state (Figure 1). The SM prediction at NNLL (nextto-next-to-leading logarithmic) order for this process at the LHC and at 8 TeV is σtsh−ch. The interest in this channel is focused on possible enhancement of its production due to new physics involving non-SM mediators, like W or charged Higgs boson [4]. The study presented here [5] analyses 19.3 fb−1 of data collected by the C√MS detector [6] in 2012 at a centre-of-mass energy s=8 TeV

Event selection and multivariate analysis

Signal extraction and results