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Multi-W Events at LHC from a Warped Extra Dimension with Custodial Symmetry

Christopher Dennis, Muge Karagoz Unel, Geraldine Servant, Jeff Tseng

TL;DR

The paper investigates the LHC prospects for discovering light Kaluza-Klein fermions predicted by warped extra-dimension models with custodial symmetry, focusing on pair-produced tilde b_R quarks that decay into tW and related channels to yield a unique 4W final state. It provides a detailed decay-width analysis for the four tilde b_R decay modes and proposes an event-selection strategy employing a leptonic W trigger and hadronic W reconstruction to distinguish the signal from dominant tt̄ and tt̄H backgrounds. Using CalcHEP and PYTHIA, the authors show sizable 4W+2b yields for m_tilde_b_R ~ 500 GeV and illustrate how additional custodians can boost the signal, with a characteristic dijet mass peak around the W mass. The study outlines further analysis directions, including leptonic signatures and full reconstruction to differentiate custodians, and emphasizes the need for more detailed detector studies to map the discovery potential at ATLAS or ILC.

Abstract

Randall-Sundrum models based on SU(2)_L * SU(2)_R with custodial symmetry are compelling frameworks for building alternative models of electroweak symmetry breaking. A particular feature of these models is the likely presence of light Kaluza-Klein fermions related to the right-handed top quark. These can be as light as a few hundred GeV and still compatible with EW precision constraints. In this article, we study the detectability of four-W final states at the LHC, which arise from the pair-production and tW decay of light Kaluza-Klein bottom quarks as well as light Kaluza-Klein quarks carrying electric charge 5/3.

Multi-W Events at LHC from a Warped Extra Dimension with Custodial Symmetry

TL;DR

The paper investigates the LHC prospects for discovering light Kaluza-Klein fermions predicted by warped extra-dimension models with custodial symmetry, focusing on pair-produced tilde b_R quarks that decay into tW and related channels to yield a unique 4W final state. It provides a detailed decay-width analysis for the four tilde b_R decay modes and proposes an event-selection strategy employing a leptonic W trigger and hadronic W reconstruction to distinguish the signal from dominant tt̄ and tt̄H backgrounds. Using CalcHEP and PYTHIA, the authors show sizable 4W+2b yields for m_tilde_b_R ~ 500 GeV and illustrate how additional custodians can boost the signal, with a characteristic dijet mass peak around the W mass. The study outlines further analysis directions, including leptonic signatures and full reconstruction to differentiate custodians, and emphasizes the need for more detailed detector studies to map the discovery potential at ATLAS or ILC.

Abstract

Randall-Sundrum models based on SU(2)_L * SU(2)_R with custodial symmetry are compelling frameworks for building alternative models of electroweak symmetry breaking. A particular feature of these models is the likely presence of light Kaluza-Klein fermions related to the right-handed top quark. These can be as light as a few hundred GeV and still compatible with EW precision constraints. In this article, we study the detectability of four-W final states at the LHC, which arise from the pair-production and tW decay of light Kaluza-Klein bottom quarks as well as light Kaluza-Klein quarks carrying electric charge 5/3.

Paper Structure

This paper contains 11 sections, 8 equations, 12 figures.

Table of Contents

  1. Introduction
  2. Model parameters
  3. $\tilde{b}_R \rightarrow t_R W^-$ decay
  4. $\tilde{b}_R \rightarrow t_L W^-$, $\tilde{b}_R \rightarrow b_L Z$ and $\tilde{b}_R \rightarrow b_L H$ decays
  5. Decay widths
  6. Preferred decays and event selection
  7. Backgrounds
  8. Signal and background simulation
  9. Trigger strategy and event reconstruction
  10. Further analysis directions
  11. Conclusion and future prospects

Figures (12)

  • Figure 1: Dominant channels for pair production of $\tilde{b}_R$.
  • Figure 2: The four decay channels of $\tilde{b}_R$.
  • Figure 3: Diagram leading to $W_R^{\pm}-W_L^{\pm}$ mixing.
  • Figure 4: Decay widths of $\tilde{b}_R$ as a function of its mass and corresponding branching ratios.
  • Figure 5: Pair production cross section for $\tilde{b}_R$ at the LHC. Only masses above the $t+W$ threshold are considered.
  • ...and 7 more figures