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Measurement of the ttbar production cross section in pp collisions at sqrt(s) = 8 TeV in dilepton final states containing one tau lepton

CMS Collaboration

TL;DR

This CMS study measures the ttbar production cross section in pp collisions at sqrt(s)=8 TeV using dilepton final states with one electron or muon and one hadronically decaying tau, based on 19.6 fb^-1 of data. The analysis relies on data-driven estimates for misidentified tau backgrounds, a hadronic tau reconstruction (tau_h) via the hadron-plus-strips method, and a kinematic reconstruction (KINb) to study top-quark related observables. The per-channel results are 255 pb and 258 pb, with a BLUE combination of 257 pb, all consistent with NNLO SM predictions within uncertainties. The result validates the tau_h dilepton channel as a precise probe of ttbar production and a background constraint for charged Higgs searches, contributing to the broader program of top-quark physics at the LHC.

Abstract

The top-quark pair production cross section is measured in final states with one electron or muon and one hadronically decaying tau lepton from the process ttbar to (l nu[l]) (tau nu[tau]) bbbar, where l = e, mu. The data sample corresponds to an integrated luminosity of 19.6 inverse femtobarns collected with the CMS detector in proton-proton collisions at sqrt(s) = 8 TeV. The measured cross section sigma[ttbar] = 257 +/- 3 (stat) +/- 24 (syst) +/- 7 (lumi) pb, assuming a top-quark mass of 172.5 GeV, is consistent with the standard model prediction.

Measurement of the ttbar production cross section in pp collisions at sqrt(s) = 8 TeV in dilepton final states containing one tau lepton

TL;DR

This CMS study measures the ttbar production cross section in pp collisions at sqrt(s)=8 TeV using dilepton final states with one electron or muon and one hadronically decaying tau, based on 19.6 fb^-1 of data. The analysis relies on data-driven estimates for misidentified tau backgrounds, a hadronic tau reconstruction (tau_h) via the hadron-plus-strips method, and a kinematic reconstruction (KINb) to study top-quark related observables. The per-channel results are 255 pb and 258 pb, with a BLUE combination of 257 pb, all consistent with NNLO SM predictions within uncertainties. The result validates the tau_h dilepton channel as a precise probe of ttbar production and a background constraint for charged Higgs searches, contributing to the broader program of top-quark physics at the LHC.

Abstract

The top-quark pair production cross section is measured in final states with one electron or muon and one hadronically decaying tau lepton from the process ttbar to (l nu[l]) (tau nu[tau]) bbbar, where l = e, mu. The data sample corresponds to an integrated luminosity of 19.6 inverse femtobarns collected with the CMS detector in proton-proton collisions at sqrt(s) = 8 TeV. The measured cross section sigma[ttbar] = 257 +/- 3 (stat) +/- 24 (syst) +/- 7 (lumi) pb, assuming a top-quark mass of 172.5 GeV, is consistent with the standard model prediction.

Paper Structure

This paper contains 9 sections, 4 equations, 3 figures, 2 tables.

Table of Contents

  1. Introduction
  2. The CMS detector
  3. Data and simulation samples
  4. Event selection
  5. Background estimate
  6. Systematic uncertainties
  7. Cross section measurement
  8. Summary
  9. The CMS Collaboration

Figures (3)

  • Figure 1: The ${b}$-tagged jet multiplicity after the full event selection. The simulated contributions are normalised to the SM predicted values. The hatched area shows the total uncertainty.
  • Figure 2: Distribution of the $\tau_\mathrm{h}\xspace$$p_{\mathrm{T}}$ (top) and $E_{\mathrm{T}}^{\text{miss}}$ (bottom) after the full event selection, for the $\mathrm{e}\tau_\mathrm{h}\xspace$ and $\mu\tau_\mathrm{h}\xspace$ channels combined. The simulated contributions are normalised to the SM predicted values. The hatched area shows the total uncertainty. The last bins include the overflow events.
  • Figure 3: (top) Minimum invariant mass reconstructed by pairing the $\tau_\mathrm{h}\xspace$ with either a b-tagged jet or with the highest $p_{\mathrm{T}}$ non b-tagged jet, as described in the text. (bottom) Distribution of the reconstructed top-quark mass $m_\text{top}$ for the $\ell\tau_\mathrm{h}\xspace$ candidate events after the full event selection. Data (points) are compared with the sum of signal and background yields, for the $\mathrm{e}\tau_\mathrm{h}\xspace$ and $\mu\tau_\mathrm{h}\xspace$ channels combined. The simulated contributions are normalised to the SM predicted values. The hatched area shows the total uncertainty. The last bins include the overflow events.