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Measurement of the p anti-p to t anti-t Production Cross Section and the Top Quark Mass at sqrt{s}=1.96 TeV in the All-Hadronic Decay Mode

CDF Collaboration, T. Aaltonen

TL;DR

This study measures the ttbar production cross section and the top quark mass in the all-hadronic decay channel using 1.02 fb^-1 of p-pbar data collected with the CDF II detector at the Tevatron. A neural-network based kinematic selection plus secondary-vertex b tagging dramatically enhances signal purity in a challenging six-to-eight jet final state and a data-driven background estimate is employed. The analysis reports a ttbar cross section of 8.3 pb and a top mass of 174.0 GeV/c^2, with uncertainties that are competitive with other channels and consistent with standard model predictions. The methods and results provide an important cross-check of top quark properties and demonstrate the viability of all-hadronic ttbar measurements in a high background environment.

Abstract

We report the measurements of the t anti-t production cross section and of the top quark mass using 1.02 fb^-1 of p anti-p data collected with the CDFII detector at the Fermilab Tevatron. We select events with six or more jets on which a number of kinematical requirements are imposed by means of a neural network algorithm. At least one of these jets must be identified as initiated by a b-quark candidate by the reconstruction of a secondary vertex. The cross section is measured to be sigma_{tt}=8.3+-1.0(stat.)+2.0-1.5(syst.)+-0.5(lumi.) pb, which is consistent with the standard model prediction. The top quark mass of 174.0+-2.2(stat.)+-4.8(syst.) GeV/c^2 is derived from a likelihood fit incorporating reconstructed mass distributions representative of signal and background.

Measurement of the p anti-p to t anti-t Production Cross Section and the Top Quark Mass at sqrt{s}=1.96 TeV in the All-Hadronic Decay Mode

TL;DR

This study measures the ttbar production cross section and the top quark mass in the all-hadronic decay channel using 1.02 fb^-1 of p-pbar data collected with the CDF II detector at the Tevatron. A neural-network based kinematic selection plus secondary-vertex b tagging dramatically enhances signal purity in a challenging six-to-eight jet final state and a data-driven background estimate is employed. The analysis reports a ttbar cross section of 8.3 pb and a top mass of 174.0 GeV/c^2, with uncertainties that are competitive with other channels and consistent with standard model predictions. The methods and results provide an important cross-check of top quark properties and demonstrate the viability of all-hadronic ttbar measurements in a high background environment.

Abstract

We report the measurements of the t anti-t production cross section and of the top quark mass using 1.02 fb^-1 of p anti-p data collected with the CDFII detector at the Fermilab Tevatron. We select events with six or more jets on which a number of kinematical requirements are imposed by means of a neural network algorithm. At least one of these jets must be identified as initiated by a b-quark candidate by the reconstruction of a secondary vertex. The cross section is measured to be sigma_{tt}=8.3+-1.0(stat.)+2.0-1.5(syst.)+-0.5(lumi.) pb, which is consistent with the standard model prediction. The top quark mass of 174.0+-2.2(stat.)+-4.8(syst.) GeV/c^2 is derived from a likelihood fit incorporating reconstructed mass distributions representative of signal and background.

Paper Structure

This paper contains 19 sections, 14 equations, 22 figures, 6 tables.

Table of Contents

  1. Introduction
  2. The CDF II Detector
  3. Multijet Event Selection
  4. Multijet Trigger
  5. Preselection and Topology Requirements
  6. Neural-Network-based Kinematical Selection
  7. Tagging $b$ quarks in the Multijet Sample
  8. Background Estimate
  9. Optimization of the kinematical selection and its efficiency
  10. Cross Section Measurement
  11. Mass reconstruction
  12. Kinematical fitter
  13. Likelihood fit
  14. The Likelihood Function
  15. Verification and Calibration of the Method
  16. ...and 4 more sections

Figures (22)

  • Figure 1: $\sum E_T$ (top) and $\sum_3 E_T$ (bottom) distributions in QCD multijet (solid histogram) and $\hbox{$t\bar{t}$}$ Monte Carlo (dashed histogram) events with $6\le N_{\rm jets}\le 8$. All histograms are normalized to unity.
  • Figure 2: Aplanarity (top) and centrality (bottom) distributions in QCD multijet (solid histogram) and $\hbox{$t\bar{t}$}$ Monte Carlo (dashed histogram) events with $6\le N_{\rm jets}\le 8$. All histograms are normalized to unity.
  • Figure 3: $M_{2j}^{min}$ (top) and $M_{2j}^{max}$ (bottom) distributions in QCD multijet (solid histogram) and $\hbox{$t\bar{t}$}$ Monte Carlo (dashed histogram) events with $6\le N_{\rm jets}\le 8$. All histograms are normalized to unity.
  • Figure 4: $M_{3j}^{min}$ (top) and $M_{3j}^{max}$ (bottom) distributions in QCD multijet (solid histogram) and $\hbox{$t\bar{t}$}$ Monte Carlo (dashed histogram) events with $6\le N_{\rm jets}\le 8$. All histograms are normalized to unity.
  • Figure 5: Kinematical distributions in QCD multijet (solid histogram) and $\hbox{$t\bar{t}$}$ Monte Carlo (dashed histogram) events with $6\le N_{\rm jets}\le 8$. From top: $E_T^{\star, 1}$, $E_T^{\star, 2}$ and $\langle E_T^\star\rangle$. All histograms are normalized to unity.
  • ...and 17 more figures