Search for decays of the Higgs boson into scalar particles decaying into four or six b quarks using pp collisions at √s = 13 TeV with the ATLAS detector

A search for exotic decays of the Higgs boson H into new scalar or pseudoscalar particles that subsequently decay into b-quarks is presented. The search considers ZH production with several decay scenarios for the Higgs boson; first to a pair of identical scalars, H → 2a → 4b, second to a pair of scalars with different masses (ma1 < ma2), either directly, H → a1a2 → 4b, or via a longer decay chain, H → a1a2 → 3a1 → 6b. The analysis uses proton-proton collision data at (Formula presented) ¼ 13 TeV collected with the ATLAS detector at the Large Hadron Collider, corresponding to an integrated luminosity of 140 fb−1. No significant excess above the Standard Model prediction is observed. The search sets upper limits at 95% confidence level on the ratio of the Higgs boson production cross section to the SM prediction times the branching ratio of Higgs bosons decaying into 4b or 6b, between 4% and 25% for σðZHÞ=σSMðZHÞ × BðH → 2a → 4bÞ, between 24% and 38% for σðZHÞ=σSMðZHÞ × BðH → a1a2 → 4bÞ, and between 10% and 20% for σðZHÞ=σSMðZHÞ × BðH → a1a2 → 3a1 → 6bÞ, depending on the masses of the scalar particles. © 2025 CERN, for the ATLAS Collaboration