Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

NLO QCD corrections to W+ W- b anti-b production with leptonic decays in the light of top quark mass and asymmetry measurements

Gudrun Heinrich, Andreas Maier, Richard Nisius, Johannes Schlenk, Jan Winter

TL;DR

This work delivers a complete NLO QCD treatment of $pp$ and $p\bar p\to W^+W^-b\bar{b}$ with leptonic $W$ decays in the 5-flavour scheme, including non-resonant and singly resonant top contributions, while applying the complex-mass scheme for top quarks and preserving spin correlations in decays. By comparing full $WWb\bar{b}$ calculations to a narrow-width, factorized $t\bar{t}$ approach, it assesses non-factorizing effects and their impact on precision observables such as the $m_{lb}$ distribution used for top mass extraction, as well as on top-quark and leptonic asymmetries. The study finds a strong reduction of scale uncertainties at NLO (from ~30% to ~5% for the total cross section) but shows that non-factorizing contributions can significantly distort $m_{lb}$ and shift the inferred top mass by up to roughly 2 GeV when LO templates are used. It also provides quantified predictions for charge asymmetries, highlighting robust relations (e.g., $A^{C}_{ll}/A^{C}_{t\bar{t}}$) and their sensitivity to kinematic cuts and scale choices, thereby guiding precision top-quark measurements and asymmetry studies at the LHC and Tevatron.

Abstract

We present the NLO QCD corrections to the processes p p and p anti-p to W+ W- b anti-b including leptonic decays of the W bosons. Non-resonant contributions as well as diagrams with doubly resonant and singly resonant top quark propagators are fully taken into account. We employ the narrow width approximation to perform the decays of the W bosons; spin correlations are however preserved. We also calculate observables relevant for top quark mass measurements, and study the impact of kinematical requirements and different scale choices on t anti-t asymmetries.

NLO QCD corrections to W+ W- b anti-b production with leptonic decays in the light of top quark mass and asymmetry measurements

TL;DR

This work delivers a complete NLO QCD treatment of and with leptonic decays in the 5-flavour scheme, including non-resonant and singly resonant top contributions, while applying the complex-mass scheme for top quarks and preserving spin correlations in decays. By comparing full calculations to a narrow-width, factorized approach, it assesses non-factorizing effects and their impact on precision observables such as the distribution used for top mass extraction, as well as on top-quark and leptonic asymmetries. The study finds a strong reduction of scale uncertainties at NLO (from ~30% to ~5% for the total cross section) but shows that non-factorizing contributions can significantly distort and shift the inferred top mass by up to roughly 2 GeV when LO templates are used. It also provides quantified predictions for charge asymmetries, highlighting robust relations (e.g., ) and their sensitivity to kinematic cuts and scale choices, thereby guiding precision top-quark measurements and asymmetry studies at the LHC and Tevatron.

Abstract

We present the NLO QCD corrections to the processes p p and p anti-p to W+ W- b anti-b including leptonic decays of the W bosons. Non-resonant contributions as well as diagrams with doubly resonant and singly resonant top quark propagators are fully taken into account. We employ the narrow width approximation to perform the decays of the W bosons; spin correlations are however preserved. We also calculate observables relevant for top quark mass measurements, and study the impact of kinematical requirements and different scale choices on t anti-t asymmetries.

Paper Structure

This paper contains 12 sections, 15 equations, 14 figures.

Table of Contents

  1. Introduction
  2. Calculational framework and numerical results
  3. Treatment of top quarks
  4. General input parameters
  5. Numerical results for LHC collisions at $7\mathrm{\:TeV}$
  6. Phenomenological studies
  7. Top quark mass measurements
  8. Mass determination using the $m_{lb}\xspace$ observable
  9. Parton level $m_{lb}\xspace$ predictions at NLO
  10. Investigation of theoretical uncertainties in the $m_{t}\xspace$ measurement
  11. Top quark asymmetries
  12. Conclusions

Figures (14)

  • Figure 1: Representative tree-level Feynman diagrams for resonant (\ref{['sfig:res']}), singly resonant (\ref{['sfig:sres']}) and non-resonant (\ref{['sfig:nres']}) contributions.
  • Figure 2: Examples of one-loop Feynman diagrams contributing to the full calculation: a non-resonant diagram (\ref{['sfig:nresloop']}) and a non-factorizable virtual contribution (\ref{['sfig:nfacloop']}).
  • Figure 3: Scale variation of the LO and NLO cross sections in the full approach (\ref{['sfig:scale']}), ranging from $x=1/4$ to $x=16$ where $x=2\,\mu/\hat{H}_T$ and $\mu=\mu_{\textrm{\tiny R}}=\mu_{\textrm{\tiny F}}$. Transverse momentum distribution of the leading $b$ jet at LO and NLO in the full approach (\ref{['sfig:ptbmax']}). The bands were obtained by varying $\mu$ by a factor of two around the central scale $\hat{H}_T/2$.
  • Figure 4: Differential distributions of the $\upDelta R$ separation (\ref{['sfig:rll']}) and the relative azimuthal angle between the two charged leptons (\ref{['sfig:phi']}) in $W^+W^-b\bar{b}$ production at LO and NLO (in the full approach). The bands were obtained by varying the scales by a factor of two around the central scale $\hat{H}_T/2$.
  • Figure 5: Transverse momentum spectra of (\ref{['sfig:ptll']}) the charged lepton pair and (\ref{['sfig:ptbb']}) the $b\bar{b}$ system, i.e. the system consisting of the two leading $b$ jets, in $W^+W^-b\bar{b}$ production at LO and NLO (in the full approach). The bands were obtained by varying the scales by a factor of two around the central scale $\hat{H}_T/2$.
  • ...and 9 more figures