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Search for single top quark production in ppbar collisions at sqrt(s)=1.96 TeV

D0 Collaboration, V Abazov

TL;DR

The paper reports a search for electroweak single top quark production in the s- and t-channels using neural-network–based signal-background discrimination with 230 pb^{-1} of DØ data at 1.96 TeV. No evidence for a signal is found, and Bayesian 95% C.L. upper limits are established: 6.4 pb for the s-channel and 5.0 pb for the t-channel, with expected limits close to these values. The analysis combines electron and muon channels, uses b-tagging to enrich signal, and leverages NN output shapes to exploit background differences. The results significantly improve previous limits and probe parameter spaces relevant to beyond-Standard-Model scenarios, such as a fourth quark generation or FCNC processes.

Abstract

We present a search for electroweak production of single top quarks in the s-channel and t-channel using neural networks for signal-background separation. We have analyzed 230 pb$^{-1}$ of data collected with the D0 detector at the Fermilab Tevatron Collider at a center-of-mass energy of 1.96 TeV and find no evidence for a single top quark signal. The resulting 95% confidence level upper limits on the single top quark production cross sections are 6.4 pb in the s-channel and 5.0 pb in the t-channel.

Search for single top quark production in ppbar collisions at sqrt(s)=1.96 TeV

TL;DR

The paper reports a search for electroweak single top quark production in the s- and t-channels using neural-network–based signal-background discrimination with 230 pb^{-1} of DØ data at 1.96 TeV. No evidence for a signal is found, and Bayesian 95% C.L. upper limits are established: 6.4 pb for the s-channel and 5.0 pb for the t-channel, with expected limits close to these values. The analysis combines electron and muon channels, uses b-tagging to enrich signal, and leverages NN output shapes to exploit background differences. The results significantly improve previous limits and probe parameter spaces relevant to beyond-Standard-Model scenarios, such as a fourth quark generation or FCNC processes.

Abstract

We present a search for electroweak production of single top quarks in the s-channel and t-channel using neural networks for signal-background separation. We have analyzed 230 pb of data collected with the D0 detector at the Fermilab Tevatron Collider at a center-of-mass energy of 1.96 TeV and find no evidence for a single top quark signal. The resulting 95% confidence level upper limits on the single top quark production cross sections are 6.4 pb in the s-channel and 5.0 pb in the t-channel.

Paper Structure

This paper contains 8 sections, 4 figures, 3 tables.

Table of Contents

  1. Introduction
  2. The DØ Detector
  3. Data Set and event selection
  4. Acceptances and Yields
  5. Neural Networks analysis
  6. Systematic uncertainties
  7. Cross section limits
  8. Conclusions

Figures (4)

  • Figure 1: Representative Feynman diagrams for electroweak top quark production at the Tevatron Collider. This figure shows (a) the $s$-channel and (b) the $t$-channel.
  • Figure 2: Comparison of signal, background, and data for the electron and muon channels combined, requiring at least one tag, for four representative neural network input variables. Shown are (a) the transverse momentum of the leading untagged jet, (b) the invariant mass of the reconstructed top quark using the leading tagged jet, (c) the invariant mass of the final state system, and (d) the pseudorapidity of the leading untagged jet multiplied by the charge of the lepton. Signals are multiplied by ten.
  • Figure 3: Comparison of signal, background, and data for the neural network outputs, for the electron and muon channels combined, requiring at least one tag. This figure shows (a) the $tb$-$t\bar{t}$ filter, (b) the $tqb$-$t\bar{t}$ filter, (c) the $tb$-$Wb\bar{b}$ filter, and (d) the $tqb$-$Wb\bar{b}$ filter. Signals are multiplied by ten.
  • Figure 4: The Bayesian posterior probability density as a function of the single top quark cross section for the $s$-channel and $t$-channel searches.