Search for Higgs boson decays into a $Z$ boson and a light hadronically decaying resonance in $pp$ collisions at $\sqrt{s}$=13 TeV with the ATLAS detector

Abstract

A search for decays of the Higgs boson into a $Z$ boson and a light resonance, with a mass of 0.5-3.5 GeV, is performed using the full 140 fb${}^{-1}$ dataset of 13 TeV proton-proton collisions recorded by the ATLAS detector during Run 2 of the LHC. Leptonic decays of the $Z$ boson and hadronic decays of the light resonance are considered. The resonance can be interpreted as a $J/\psi$ or ${\eta }_c$ meson, an axion-like particle, or a light pseudoscalar in two-Higgs-doublet models. Due to its low mass, it would be produced with high boost and reconstructed as a single small-radius jet of hadrons. A neural network is used to correct the Monte Carlo simulation of the background in a data-driven way. Two additional neural networks are used to distinguish signal from background. A binned profile-likelihood fit is performed on the final-state invariant mass distribution. No significant excess of events relative to the expected background is observed, and upper limits at 95% confidence level are set on the Higgs boson's branching fraction to a $Z$ boson and a light resonance. The exclusion limit is ~10% for the lower masses, and increases for higher masses. Upper limits on the effective coupling $C_{ZH}^{\text{eff}}/\Lambda$ of an axion-like particle to a Higgs boson and $Z$ boson are also set at 95% confidence level, and range from 0.9 to 2 TeV${}^{-1}$.

arXiv comment37 pages in total, author list starting page 20, 10 (sub)figures, 0 tables, published in Phys. Lett. B. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HDBS-2021-09/

References in corpus (52)

• Observation of a new particle in the search for the Standard Model Higgs boson with the ATLAS detector at the LHC
• Observation of a new boson at a mass of 125 GeV with the CMS experiment at the LHC
• The anti-k_t jet clustering algorithm
• An Introduction to PYTHIA 8.2
• FastJet user manual
• New Generation of Parton Distributions with Uncertainties from Global QCD Analysis
• Asymptotic formulae for likelihood-based tests of new physics
• A general framework for implementing NLO calculations in shower Monte Carlo programs: the POWHEG BOX
• A New Method for Combining NLO QCD with Shower Monte Carlo Algorithms
• Matching NLO QCD computations with Parton Shower simulations: the POWHEG method
• Theory and phenomenology of two-Higgs-doublet models
• Parton distributions for the LHC Run II
• Parton distributions with LHC data
• The ATLAS Simulation Infrastructure
• PDF4LHC recommendations for LHC Run II
• Event Generation with Sherpa 2.2
• Pileup subtraction using jet areas
• An NNLO subtraction formalism in hadron collisions and its application to Higgs boson production at the LHC
• The CP-conserving two-Higgs-doublet model: the approach to the decoupling limit
• High-precision QCD at hadron colliders: electroweak gauge boson rapidity distributions at NNLO
• Identifying Boosted Objects with N-subjettiness
• Performance of the ATLAS Trigger System in 2015
• Performance of pile-up mitigation techniques for jets in $pp$ collisions at $\sqrt{s}=8$ TeV using the ATLAS detector
• Electron and photon performance measurements with the ATLAS detector using the 2015-2017 LHC proton-proton collision data
• The Next-to-Minimal Supersymmetric extension of the Standard Model reviewed
• A portrait of the Higgs boson by the CMS experiment ten years after the discovery
• A detailed map of Higgs boson interactions by the ATLAS experiment ten years after the discovery
• Jet reconstruction and performance using particle flow with the ATLAS Detector
• Exotic Decays of the 125 GeV Higgs Boson
• Performance of electron and photon triggers in ATLAS during LHC Run 2
• Muon reconstruction and identification efficiency in ATLAS using the full Run 2 $pp$ collision data set at $\sqrt{s}=13$ TeV
• ATLAS data quality operations and performance for 2015-2018 data-taking
• Jet energy scale and resolution measured in proton-proton collisions at $\sqrt{s}=13$ TeV with the ATLAS detector
• Performance of the ATLAS muon triggers in Run 2
• MINLO: Multi-scale improved NLO
• Merging H/W/Z + 0 and 1 jet at NLO with no merging scale: a path to parton shower + NNLO matching
• Substructure of high-p_T Jets at the LHC
• Dark Matter through the Higgs portal
• Luminosity determination in $pp$ collisions at $\sqrt{s}=13$ TeV using the ATLAS detector at the LHC
• New Angles on Energy Correlation Functions
• NLO Higgs boson production plus one and two jets using the POWHEG BOX, MadGraph4 and MCFM
• Performance of the ATLAS Track Reconstruction Algorithms in Dense Environments in LHC Run 2
• The N2HDM under Theoretical and Experimental Scrutiny
• Probing the nature of the Higgs-like Boson via h -> VF decays
• The Minimal Supersymmetric Standard Model (MSSM)
• The Next-to-Minimal Two Higgs Doublet Model
• The quest for axions and other new light particles
• The ATLAS Inner Detector Trigger performance in pp collisions at 13 TeV during LHC Run 2
• Challenges for an axion explanation of the muon $g-2$ measurement
• ALP dark matter with non-periodic potentials: parametric resonance, halo formation and gravitational signatures
• Search for short- and long-lived axion-like particles in $H\to aa\to 4\gamma$ decays with the ATLAS experiment at the LHC
• Search for exotic decays of the Higgs boson to a pair of pseudoscalars in the $\mu \mu$bb and $\tau \tau$bb final states