TOP-13-009
Search for the single-top production in the s channel at 8 TeV

Abstract

Search for the single-top production in $s$ channel in proton-proton collisions at a centre-of-mass energy of \sqrt{s} = 8 TeV by the CMS detector at the LHC is presented. The 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. The study on 19.3 fb−1 of data collected during 2012 leads to an upper limit on the cross section times branching ratio of 11.5 pb at 95% confidence level.

Public Document

The public document CMS-PAS-TOP-13-009 can be found here: link

Results

Upper limit

ul-sjort.png The observed and expected upper limits, the latter quoted as (SM signal, background-only), on the s-channel cross section using a Bayesian approach.

Cross section

xsection.png Single top-quark s-channel cross section measurement

xsectionFC.png Measured cross sections reported using the Feldman-Cousins unified approach to determine the correct 68% confidence interval in presence of a physical boundary (non negative cross section)

Figures

Figure Caption

BDT discriminant:

Data-simulation comparison for the distributions of the BDT discriminator in the 2-jets 2-tags sample , electron channel. The simulation is normalized to the combined (muons plus electrons) fit results. The smaller error bands include the background rates uncertainties only, the larger ones include the total systematic uncertainty, obtained summing in quadrature the individual contributions. pdf

Data-simulation comparison for the distributions of the BDT discriminator in the 3-jets 2-tags sample , electron channel. The simulation is normalized to the combined (muons plus electrons) fit results. The smaller error bands include the background rates uncertainties only, the larger ones include the total systematic uncertainty, obtained summing in quadrature the individual contributions. pdf

Data-simulation comparison for the distributions of the BDT discriminator in the 2-jets 2-tags sample , muon channel. The simulation is normalized to the combined (muons plus electrons) fit results. The smaller error bands include the background rates uncertainties only, the larger ones include the total systematic uncertainty, obtained summing in quadrature the individual contributions. pdf

Data-simulation comparison for the distributions of the BDT discriminator in the 3-jets 2-tags sample , muon channel. The simulation is normalized to the combined (muons plus electrons) fit results. The smaller error bands include the background rates uncertainties only, the larger ones include the total systematic uncertainty, obtained summing in quadrature the individual contributions. pdf

BDT input variables:

Data compared to the MC models for the transvers mass of W, one of the highest ranked variables in 2-jets 2-tags in the electron channel. The simulation is normalised to the muons plus electrons fit results. The smaller error bands include the background rates uncertainties only, the larger ones include all the systematic uncertainties. pdf

Data compared to the MC models for the ΔφTop, recoiled b jet aginst top , one of the highest ranked variables in 2-jets 2-tags in the electron channel. The simulation is normalised to the muons plus electrons fit results. The smaller error bands include the background rates uncertainties only, the larger ones include all the systematic uncertainties. pdf

Data compared to the MC models for the missing transvers energy, one of the highest ranked variables in 2-jets 2-tags in the electron channel. The simulation is normalised to the muons plus electrons fit results. The smaller error bands include the background rates uncertainties only, the larger ones include all the systematic uncertainties. pdf

Data compared to the MC models for the ηj(pseudorapidity of the jet which is not b tagged), one of the highest ranked variables in 3-jets 2-tags in the electron channel. The simulation is normalised to the muons plus electrons fit results. The smaller error bands include the background rates uncertainties only, the larger ones include all the systematic uncertainties. pdf

3J2T_HT_normTocombinedfit_errbands_EleStack.png Data compared to the MC models for the HT (scalar sum of pT of all jets) one of the highest ranked variables in 3-jets 2-tags in the electron channel. The simulation is normalised to the muons plus electrons fit results. The smaller error bands include the background rates uncertainties only, the larger ones include all the systematic uncertainties. pdf

Data compared to the MC models for the ΔRleading jet,second jet, one of the highest ranked variables in 3-jets 2-tags in the electron channel. The simulation is normalised to the muons plus electrons fit results. The smaller error bands include the background rates uncertainties only, the larger ones include all the systematic uncertainties. pdf

Data compared to the MC models for the vector sum of pT of the two b-tagged jets , one of the highest ranked variables in 2-jets 2-tags in the muon channel. The simulation is normalised to the muons plus electrons fit results. The smaller error bands include the background rates uncertainties only, the larger ones include all the systematic uncertainties. pdf

Data compared to the MC models for the top quark mass , one of the highest ranked variables in 2-jets 2-tags in the muon channel. The simulation is normalised to the muons plus electrons fit results. The smaller error bands include the background rates uncertainties only, the larger ones include all the systematic uncertainties. pdf

Data compared to the MC models for the transvers mass of W , one of the highest ranked variables in 2-jets 2-tags in the muon channel. The simulation is normalised to the muons plus electrons fit results. The smaller error bands include the background rates uncertainties only, the larger ones include all the systematic uncertainties. pdf

Data compared to the MC models for the transvers mass of W , one of the highest ranked variables in 3-jets 2-tags in the muon channel. The simulation is normalised to the muons plus electrons fit results. The smaller error bands include the background rates uncertainties only, the larger ones include all the systematic uncertainties. pdf

Data compared to the MC models for the cosθ*(cosine of the angle between the lepton and the recoil jet in top quark rest frame ) , one of the highest ranked variables in 3-jets 2-tags in the muon channel. The simulation is normalised to the muons plus electrons fit results. The smaller error bands include the background rates uncertainties only, the larger ones include all the systematic uncertainties. pdf

Data compared to the MC models for the invariant mass of the two b-tagged jets, one of the highest ranked variables in 3-jets 2-tags in the muon channel. The simulation is normalised to the muons plus electrons fit results. The smaller error bands include the background rates uncertainties only, the larger ones include all the systematic uncertainties. pdf

Tables

inputEle.png Input variables for BDT training in the 2-jets 2-tags sample, ranked by their importance, in the electron channel.

inputMu.png Input variables for BDT training in the 2-jets 2-tags sample, ranked by their importance, in the muon channel.

yield.png Event yield for the main processes in the 3-jets 2-tags and 2-jets 2-tags region. The
yields of the simulated samples are quoted after the likelihood maximization procedure for the common muons plus electrons fit. The uncertainty includes the statistical uncertainty on the simulation, the rate uncertainties and the b-tagging uncertainty.

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