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Single Top Quark at Future Hadron Colliders. Complete Signal and Background Study

A. S. Belyaev, E. E. Boos, L. V. Dudko

TL;DR

This work tackles the challenge of measuring single top production and the $Wtb$ coupling at hadron colliders by developing a complete Monte Carlo framework that couples CompHEP matrix elements to PYTHIA/JETSET, includes initial- and final-state radiation, jet fragmentation, and realistic detector effects. It explicitly incorporates the QCD fake background, performs a detailed comparison of signal and background kinematic properties, and devises a cascade of cuts that reduce backgrounds by large factors while preserving a significant fraction of the signal. The study finds that after optimized cuts the signal-to-background ratio reaches about $0.4$ at the Tevatron and ~1 at the LHC, with a post-cut lepton+jets signal rate around ${6.1}$ pb at the LHC, implying substantial event yields for $V_{tb}$ measurements. The results underscore the feasibility of early single-top measurements at the LHC, highlight the need for NLO refinements and precise PDFs/top-quark mass inputs, and provide a quantitative framework for background suppression and signal extraction in future collider analyses.

Abstract

We perform a detail theoretical study including decays and jet fragmentation of all the important modes of the single top quark production and all basic background processes at the upgraded Tevatron and LHC colliders. Special attention was paid to the complete tree level calculation of the QCD fake background which was not considered in the previous studies. Analysis of the various kinematical distributions for the signal and backgrounds allowed to work out a set of cuts for an efficient background suppression and extraction of the signal. It was shown that the signal to background ratio after optimized cuts could reach about 0.4 at the Tevatron and 1 at the LHC. The remaining after cuts rate of the signal at the LHC for the $lepton+jets $ signature is expected to be about 6.1 pb and will be enough to study the single top physics even during the LHC operation at a low luminosity.

Single Top Quark at Future Hadron Colliders. Complete Signal and Background Study

TL;DR

This work tackles the challenge of measuring single top production and the coupling at hadron colliders by developing a complete Monte Carlo framework that couples CompHEP matrix elements to PYTHIA/JETSET, includes initial- and final-state radiation, jet fragmentation, and realistic detector effects. It explicitly incorporates the QCD fake background, performs a detailed comparison of signal and background kinematic properties, and devises a cascade of cuts that reduce backgrounds by large factors while preserving a significant fraction of the signal. The study finds that after optimized cuts the signal-to-background ratio reaches about at the Tevatron and ~1 at the LHC, with a post-cut lepton+jets signal rate around pb at the LHC, implying substantial event yields for measurements. The results underscore the feasibility of early single-top measurements at the LHC, highlight the need for NLO refinements and precise PDFs/top-quark mass inputs, and provide a quantitative framework for background suppression and signal extraction in future collider analyses.

Abstract

We perform a detail theoretical study including decays and jet fragmentation of all the important modes of the single top quark production and all basic background processes at the upgraded Tevatron and LHC colliders. Special attention was paid to the complete tree level calculation of the QCD fake background which was not considered in the previous studies. Analysis of the various kinematical distributions for the signal and backgrounds allowed to work out a set of cuts for an efficient background suppression and extraction of the signal. It was shown that the signal to background ratio after optimized cuts could reach about 0.4 at the Tevatron and 1 at the LHC. The remaining after cuts rate of the signal at the LHC for the signature is expected to be about 6.1 pb and will be enough to study the single top physics even during the LHC operation at a low luminosity.

Paper Structure

This paper contains 6 sections, 5 equations, 7 figures, 5 tables.

Table of Contents

  1. Introduction
  2. MC simulation
  3. Signal
  4. Main backgrounds
  5. Signal and background kinematical properties
  6. Conclusions

Figures (7)

  • Figure 1: Diagrams for single top production
  • Figure 2: Diagrams for $Wb\bar{b}$ background
  • Figure 3: Distribution for $p_T$ of the second jet for $jjb\bar{b}$ process for exact calculation (solid line) and for splitting from $jb\bar{b}$ process (dashed line) at Tevatron.
  • Figure 4: Distributions for signal and background for the some most spectacular variables at Tevatron. Sketched histogram stands for signal.
  • Figure 5: Distributions for signal and background for the some most spectacular variables at LHC. Sketched histogram stands for signal.
  • ...and 2 more figures