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Complete Calculations of Wb\bar b and Wb\bar b + jet Production at Tevatron and LHC: Probing Anomalous Wtb Couplings in Single Top Production

Edward Boos, Lev Dudko, Thorsten Ohl

TL;DR

This work presents a complete tree-level analysis of $pp(\bar p)\to Wb\bar b$ and $Wb\bar b+\text{jet}$ to probe anomalous $Wtb$ couplings at the Tevatron and LHC. By analyzing Feynman-diagram singularities, the authors identify sensitive observables and devise optimized cuts that dramatically suppress backgrounds while preserving the single-top signal; they implement the calculation in CompHEP and include known NLO corrections to single-top production. They study two magnetic form factors, $F_2^L$ and $F_2^R$, within an effective Lagrangian, and derive 2σ exclusion contours for both Tevatron and LHC, showing the LHC can improve sensitivity by a factor of 2–3 over the upgraded Tevatron, especially when both final states and asymmetries are used. Systematic uncertainties significantly affect the exact bounds, highlighting the importance of precise control of systematics and double $b$-tagging; the results are contrasted with future high-energy $\gamma e$ colliders, and the potential for combining with CLEO constraints is discussed. Overall, the study provides a framework and quantitative expectations for directly probing the $Wtb$ vertex at hadron colliders.

Abstract

We present the results of a complete tree level calculation of the processes pp(\bar p) -> Wb\bar b and Wb\bar b + jet that includes the single top signal and all irreducible backgrounds simultaneously. In order to probe the structure of the Wtb coupling with the highest possible accuracy and to look for possible deviations from standard model predictions, we identify sensitive observables and propose an optimal set of cuts which minimizes the background compared to the signal. At the LHC, the single top and the single anti-top rates are different and the corresponding asymmetry yields additional information. The analysis shows that the sensitivity for anomalous couplings will be improved at the LHC by a factor of 2--3 compared to the expectations for the first measurements at the upgraded Tevatron. Still, the bounds on anomalous couplings obtained at hadron colliders will remain 2--8 times larger than those from high energy gamma-e colliders, which will, however, not be available for some time. All basic calculations have been carried out using the computer package CompHEP. The known NLO corrections to the single top rate have been taken into account.

Complete Calculations of Wb\bar b and Wb\bar b + jet Production at Tevatron and LHC: Probing Anomalous Wtb Couplings in Single Top Production

TL;DR

This work presents a complete tree-level analysis of and to probe anomalous couplings at the Tevatron and LHC. By analyzing Feynman-diagram singularities, the authors identify sensitive observables and devise optimized cuts that dramatically suppress backgrounds while preserving the single-top signal; they implement the calculation in CompHEP and include known NLO corrections to single-top production. They study two magnetic form factors, and , within an effective Lagrangian, and derive 2σ exclusion contours for both Tevatron and LHC, showing the LHC can improve sensitivity by a factor of 2–3 over the upgraded Tevatron, especially when both final states and asymmetries are used. Systematic uncertainties significantly affect the exact bounds, highlighting the importance of precise control of systematics and double -tagging; the results are contrasted with future high-energy colliders, and the potential for combining with CLEO constraints is discussed. Overall, the study provides a framework and quantitative expectations for directly probing the vertex at hadron colliders.

Abstract

We present the results of a complete tree level calculation of the processes pp(\bar p) -> Wb\bar b and Wb\bar b + jet that includes the single top signal and all irreducible backgrounds simultaneously. In order to probe the structure of the Wtb coupling with the highest possible accuracy and to look for possible deviations from standard model predictions, we identify sensitive observables and propose an optimal set of cuts which minimizes the background compared to the signal. At the LHC, the single top and the single anti-top rates are different and the corresponding asymmetry yields additional information. The analysis shows that the sensitivity for anomalous couplings will be improved at the LHC by a factor of 2--3 compared to the expectations for the first measurements at the upgraded Tevatron. Still, the bounds on anomalous couplings obtained at hadron colliders will remain 2--8 times larger than those from high energy gamma-e colliders, which will, however, not be available for some time. All basic calculations have been carried out using the computer package CompHEP. The known NLO corrections to the single top rate have been taken into account.

Paper Structure

This paper contains 6 sections, 6 equations, 10 figures, 4 tables.

Table of Contents

  1. Introduction
  2. The Basic Processes
  3. Anomalous $Wtb$ Couplings
  4. Sensitive Variables, Background Suppression and the Structure of Singularities in Feynman Diagrams
  5. Distributions and numerical results
  6. Conclusions

Figures (10)

  • Figure 1: Feynman diagrams for the process $u\bar{d}\to b\bar{b}W$.
  • Figure 2: Feynman diagrams for the process $u\bar{d}\to gb\bar{b}W$.
  • Figure 3: Distributions for invariant masses and transverse momenta for the process $p\bar{p}\to b\bar{b}W$ at Tevatron using the soft cuts in (\ref{['eq:soft-cuts@TeV']}).
  • Figure 4: Distributions for invariant masses and transverse momenta for the process $p\bar{p}\to b\bar{b}W$ at LHC using the soft cuts in (\ref{['eq:soft-cuts@LHC']}).
  • Figure 5: Distributions for invariant masses and transverse momenta for the process $pp\to jb\bar{b}W$ at Tevatron using the soft cuts in (\ref{['eq:soft-cuts@TeV']}).
  • ...and 5 more figures