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The t W- Mode of Single Top Production

Tim M. P. Tait

TL;DR

The paper investigates the tW- mode of single top production as a probe of the top quark's weak coupling, computing the inclusive rate with large logarithmic corrections resummed into the bottom PDF. It develops a subtraction framework to avoid double counting with on-shell t tbar production and collinear regions, and analyzes the resulting corrections, finding a modest net shift at the LHC. A LO 2->2 description plus ${\cal O}(1/\log (m_t^2/m_b^2))$ 2->3 corrections is matched within a coherent scheme. A comprehensive parton-level MC study at the LHC demonstrates that the tW- signal can be extracted from major backgrounds with realistic cuts and b-tagging, suggesting observability at relatively low luminosity and motivating further higher-order calculations to reduce theoretical uncertainties.

Abstract

The t W- mode of single top production is proposed as an important means to study the weak interactions of the top quark. While the rate of this mode is most likely too small to be observed at Run II of the Fermilab Tevatron, it is expected to be considerably larger at the CERN LHC. In this article the inclusive t W- rate is computed, including O(1 / log (m_t^2 / m_b^2)) corrections, and when combined with detailed Monte Carlo simulations including the top and W decay products, indicate that the t W- single top process may be extracted from the considerable t tbar and W+ W- j backgrounds at low luminosity runs of the LHC.

The t W- Mode of Single Top Production

TL;DR

The paper investigates the tW- mode of single top production as a probe of the top quark's weak coupling, computing the inclusive rate with large logarithmic corrections resummed into the bottom PDF. It develops a subtraction framework to avoid double counting with on-shell t tbar production and collinear regions, and analyzes the resulting corrections, finding a modest net shift at the LHC. A LO 2->2 description plus 2->3 corrections is matched within a coherent scheme. A comprehensive parton-level MC study at the LHC demonstrates that the tW- signal can be extracted from major backgrounds with realistic cuts and b-tagging, suggesting observability at relatively low luminosity and motivating further higher-order calculations to reduce theoretical uncertainties.

Abstract

The t W- mode of single top production is proposed as an important means to study the weak interactions of the top quark. While the rate of this mode is most likely too small to be observed at Run II of the Fermilab Tevatron, it is expected to be considerably larger at the CERN LHC. In this article the inclusive t W- rate is computed, including O(1 / log (m_t^2 / m_b^2)) corrections, and when combined with detailed Monte Carlo simulations including the top and W decay products, indicate that the t W- single top process may be extracted from the considerable t tbar and W+ W- j backgrounds at low luminosity runs of the LHC.

Paper Structure

This paper contains 8 sections, 10 equations, 4 figures, 3 tables.

Table of Contents

  1. Introduction
  2. The inclusive $t \, W^-~$ Rate
  3. Leading Order $2 \rightarrow 2$ Contributions
  4. ${\cal O}( 1 / \log m_t^2 / m_b^2 )$ $2 \rightarrow 3$ Corrections
  5. Extracting $t \, W^-~$ from the Background
  6. Conclusions
  7. Acknowledgements
  8. Helicity amplitudes for $b \, g \rightarrow t \, W^- \rightarrow b e^+ \nu_e \mu^- \bar{\nu_\mu}$

Figures (4)

  • Figure 1: The underlying picture for production of $t \, W^-~$ at a $p p$ or $p \bar{p}$ collider. The crossed circle on the bottom quark line anticipates the improvement of the perturbation series by resumming the $g \rightarrow b \, \bar{b}$ portion of the interaction into a $b$ parton density.
  • Figure 2: Feynman diagrams for the $t \, W^-$ mode of single top production after resumming large logarithms into a gluon PDF: $g \, b \rightarrow t \, W^-$.
  • Figure 3: Representative Feynman diagrams for corrections to the $t \, W^-$ mode of single top production corresponding to (a) large $\log$ corrections associated with the $b$ PDF, (b) LO $t \, \bar{t}$ production followed by the LO decay $\bar{t} \rightarrow W^- \, \bar{b}$, and (c) pure $\alpha_{S}$ corrections.
  • Figure 4: Illustrative Feynman diagram for the irreducible background, $W^+ \, W^- \, b~$ production, involving an off-shell top quark. The leptonic decay modes of the $W$ bosons are not indicated here.