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Measuring collinear W emissions inside jets

Frank Krauss, Petar Petrov, Marek Schoenherr, Michael Spannowsky

TL;DR

The paper investigates collinear W boson emission inside jets at the LHC by implementing electroweak radiation in SHERPA's parton shower and developing both hadronic and leptonic W-tagging strategies in dijet events at 14 TeV. Hadronic reconstruction relies on jet substructure with mass-drop and microjet techniques, supplemented by jet-shape observables such as ellipticity and tau21 to distinguish W jets from QCD background. A binned likelihood framework with systematic uncertainties quantifies sensitivity to deviations in the W-emission rate, showing that hadronic methods can exclude large deviations (f=0 or f=2) under modest systematics, while jet shapes can probe smaller changes around f≈1.1, particularly when combined with robust leptonic tagging. Leptonic analysis offers strong background rejection and higher S/B, enabling precise tests of electroweak Sudakov effects and complementing hadronic approaches in measuring EW radiation inside jets.

Abstract

Single and multiple emission of electroweak gauge bosons and in particular of W bosons is discussed in the parton shower language. Algorithms and observables for the reconstruction of both leptonically and hadronically decaying W bosons inside light quark jets are compared, and they are applied to a study of how emission rates of W bosons in light-jet events at the LHC could be measured.

Measuring collinear W emissions inside jets

TL;DR

The paper investigates collinear W boson emission inside jets at the LHC by implementing electroweak radiation in SHERPA's parton shower and developing both hadronic and leptonic W-tagging strategies in dijet events at 14 TeV. Hadronic reconstruction relies on jet substructure with mass-drop and microjet techniques, supplemented by jet-shape observables such as ellipticity and tau21 to distinguish W jets from QCD background. A binned likelihood framework with systematic uncertainties quantifies sensitivity to deviations in the W-emission rate, showing that hadronic methods can exclude large deviations (f=0 or f=2) under modest systematics, while jet shapes can probe smaller changes around f≈1.1, particularly when combined with robust leptonic tagging. Leptonic analysis offers strong background rejection and higher S/B, enabling precise tests of electroweak Sudakov effects and complementing hadronic approaches in measuring EW radiation inside jets.

Abstract

Single and multiple emission of electroweak gauge bosons and in particular of W bosons is discussed in the parton shower language. Algorithms and observables for the reconstruction of both leptonically and hadronically decaying W bosons inside light quark jets are compared, and they are applied to a study of how emission rates of W bosons in light-jet events at the LHC could be measured.

Paper Structure

This paper contains 8 sections, 7 equations, 9 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Electroweak Shower and Event Generation
  3. W reconstruction in dijet events
  4. Hadronic Analysis
  5. Leptonic Analysis
  6. Measuring W boson emission rates
  7. Conclusion
  8. Ellipticity

Figures (9)

  • Figure 1: $W$ candidate mass distribution using method \ref{['mhard']} for $p_{T_J} > 500$ (left), $750$ (center) and $1000$ (right) GeV.
  • Figure 2: $W$ candidate mass distribution based on microjets $\iota_{2}$ and $\iota_{3}$ as described in method \ref{['mmed']} for $p_{T_J} > 500$ (left), $750$ (center) and $1000$ (right) GeV.
  • Figure 3: $W$ candidate mass distribution based on method \ref{['msoft']} for $p_{T_J} > 500$ (left), $750$ (center) and $1000$ (right) GeV.
  • Figure 4: Ellipticity $\hat{t}$ (top row) and $\tau_{21}$ (bottom row) distributions calculated using constituents of $W$ candidates identified with method \ref{['mhard']} for $p_{T_J} > 500$ (left), $750$ (center) and $1000$ (right) GeV.
  • Figure 5: Transverse mass of the leptonic $W$ candidate $m_\mathrm{T}$ for $p_{T_J} > 500$ (left), $750$ (center) and $1000$ (right).
  • ...and 4 more figures