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Prospects for studying the $WHγ$ process in $pp$ collisions at the LHC

Youpeng Wu, Jie Xiao, Andrew Michael Levin, Qiang Li

TL;DR

This study assesses the prospect of observing the rare triboson process WHgamma in proton-proton collisions at the LHC as a probe of the electroweak sector and possible new physics. Using a CMS-inspired Monte Carlo setup (MadGraph_aMC@NLO, Pythia, Delphes) and Higgs decays modeled via MadSpin, the analysis employs a Boosted Decision Tree (XGBoost) to optimize event selection for the final state with a lepton, missing energy, two b-jets, and a photon. The BDT achieves strong background rejection while preserving signal, enabling a projected significance of approximately 0.63 sigma at 440 fb^{-1} and 1.64 sigma at the HL-LHC (3000 fb^{-1}). The non-Higgs photon contribution dominates the signal over the Higgs-mediated component, and, despite challenging observability, the results motivate an experimental search to constrain this multiboson final state and test electroweak couplings. The work is supported by the National Natural Science Foundation of China.

Abstract

The Standard Model of particle physics, though remarkably successful, leaves open several major questions that continue to motivate searches for new phenomena. Multiboson interactions involving the Higgs boson are of special interest as probes of the electroweak Lagrangian where potential new physics may be hiding. In this work, we present a study of the simultaneous production of a W boson, a Higgs bosons and a photon in proton-proton collisions at the Large Hadron Collider. Monte Carlo simulation is performed to model both the signal and the background processes, and detector effects are included according to CMS specifications. Boosted decision trees are employed to optimize the event selection and enhance signal-background discrimination. We estimate that with an integrated luminosity of 440~$\rm fb^{-1}$, the expected significance for the $WHγ$ process is 0.63$σ$, projected to reach 1.64$σ$ at the High-Luminosity LHC (HL-LHC).

Prospects for studying the $WHγ$ process in $pp$ collisions at the LHC

TL;DR

This study assesses the prospect of observing the rare triboson process WHgamma in proton-proton collisions at the LHC as a probe of the electroweak sector and possible new physics. Using a CMS-inspired Monte Carlo setup (MadGraph_aMC@NLO, Pythia, Delphes) and Higgs decays modeled via MadSpin, the analysis employs a Boosted Decision Tree (XGBoost) to optimize event selection for the final state with a lepton, missing energy, two b-jets, and a photon. The BDT achieves strong background rejection while preserving signal, enabling a projected significance of approximately 0.63 sigma at 440 fb^{-1} and 1.64 sigma at the HL-LHC (3000 fb^{-1}). The non-Higgs photon contribution dominates the signal over the Higgs-mediated component, and, despite challenging observability, the results motivate an experimental search to constrain this multiboson final state and test electroweak couplings. The work is supported by the National Natural Science Foundation of China.

Abstract

The Standard Model of particle physics, though remarkably successful, leaves open several major questions that continue to motivate searches for new phenomena. Multiboson interactions involving the Higgs boson are of special interest as probes of the electroweak Lagrangian where potential new physics may be hiding. In this work, we present a study of the simultaneous production of a W boson, a Higgs bosons and a photon in proton-proton collisions at the Large Hadron Collider. Monte Carlo simulation is performed to model both the signal and the background processes, and detector effects are included according to CMS specifications. Boosted decision trees are employed to optimize the event selection and enhance signal-background discrimination. We estimate that with an integrated luminosity of 440~, the expected significance for the process is 0.63, projected to reach 1.64 at the High-Luminosity LHC (HL-LHC).
Paper Structure (4 sections, 6 figures, 3 tables)

This paper contains 4 sections, 6 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Event Reconstruction and Selection
  3. BDT Training and Result
  4. Summary

Figures (6)

  • Figure 1: Feynman diagram for $WH\gamma$ signal process. Left-above: Higgs radiation, Middle-above: QED process, Right-above: $H\to Z\gamma$ process; Left-bottom: W boson decay (leptonic), Right-bottom: quark radiation. And we consider W boson decay and quark radiation as non-Higgs process.
  • Figure 2: Photon energy distribution for WHG Higgs process at 13 TeV. The QED process is processed by photon radiation from b quark, while the EW+$\gamma$ process is processed by electroweak one-loop correction with photon radiation from Higgs boson.
  • Figure 3: Left: Photon transverse momentum distribution before selection. Right: Photon transverse momentum distribution after selection. In Luminosity of 440 $\rm fb^{-1}$.
  • Figure 4: Left: Feature importance of BDT training (top 10 variables). Right: ROC curve of BDT training (AUC = 0.790).
  • Figure 5: Left: Transverse W boson mass distribution without BDT cut. Right: Transverse W boson mass distribution with BDT cut.
  • ...and 1 more figures