Jet Substructure and the Search for Neutral Spin-One Resonances in Electroweak Boson Channels

TL;DR

The paper investigates the potential to discover neutral spin-1 Z' resonances decaying to electroweak bosons at the LHC by leveraging jet substructure, focusing on highly boosted hadronic decays of Zh and W+W−. It adopts the BDRS algorithm with large fat-jet radii to identify boosted boson jets, compares substructure-based tagging with traditional jet methods, and evaluates model-independent discovery reach across WW and Zh final states. The study finds significant improvements in sensitivity, particularly for a 3 TeV Z' with fb-scale cross sections, and demonstrates that the invisible Z decay mode can be a competitive discovery channel, especially when combined with muon-based b-tagging tactics. Together, these results illustrate the utility of jet substructure as a robust, scale-invariant tool for probing TeV-scale resonances in electroweak boson channels and guide future resonance searches at the LHC.

Abstract

Strongly coupled models at the TeV scale often predict one or more neutral spin-one resonances (Z') which have appreciable branching fractions to electroweak bosons, namely the Higgs and longitudinal W and Z. These resonances are usually believed to have multi-TeV mass due to electroweak precision constraints, placing them on the edge of LHC discovery reach. Searching for them is made particularly challenging because hadronically decaying electroweak bosons produced at such high energy will appear very similar to QCD jets. In this work we revisit the possibility of discovering these resonances at the LHC, taking advantage of recently developed jet substructure techniques. We make a systematic investigation of substructure performance for the identification of highly Lorentz-boosted electroweak bosons, which should also be applicable to more general new physics searches. We then estimate the model-independent Z' discovery reach for the most promising final-state channels, and find significant improvements compared to previous analyses. For modes involving the Higgs, we focus on a light Higgs decaying to b quarks. We further highlight several other novelties of these searches. In the case that vertex-based b-tagging becomes inefficient at high p_T, we explore the utility of a muon-based b-tag, or no b-tag at all. We also introduce the mode Z' -> Zh -> (invisible)(bb) as a competitive discovery channel.

Figures (12)

• Figure 1: Distributions of the (particle-level) reconstructed hadronic $W$ mass for 1 and 3 TeV $Z'\to WW \to (l\nu)(q\bar{q}')$. Displayed are the nominal BDRS procedure (solid black), traditional dijets (dashed blue), traditional monojets (dashed red), and combined dijet+monojet (solid purple).
• Figure 2: Slices of the showered leading-order double-differential cross section for $W$+jets $\to(l\nu)$+jets vs (particle-level) reconstructed $W$ mass, fixing the reconstructed $Z'$ mass at 1 and 3 TeV. Displayed are the nominal BDRS procedure (solid black), traditional dijets (dashed blue), traditional monojets (dashed red), and combined dijet+monojet (solid purple).
• Figure 3: Reconstructed $W$-jet (left) and $h$-jet (right) invariant mass distributions for $Z'$ masses of 1 TeV (black), 2 TeV (blue), and 3 TeV (red). The rescaled ECAL model of appendix \ref{['sec:detector']} has been applied.
• Figure 4: Reconstructed $Z'$ invariant masses for 1, 2, and 3 TeV in $WW \to (l\nu)(q\bar{q}')$.
• Figure 5: Discovery reach for $WW \to (l\nu)(q\bar{q}')$. The three symbols (diamond, box, circle) correspond to (30, 100, 300) fb$^{-1}$ of integrated luminosity. The $\times$ refers to the value that is required to achieve $S/B = 1$.