Search for decays of the Higgs boson into scalar particles decaying into four or six $b$-quarks using $pp$ collisions at $\sqrt{s}= 13\,\mathrm{TeV}$ with the ATLAS detector

TL;DR

This paper reports a search for exotic Higgs decays into multiple $b$-quark final states using 13 TeV proton-proton collision data from ATLAS, setting upper limits on such decay modes without observing significant excess.

Contribution

It introduces a search for Higgs decays into scalar particles decaying into four or six $b$-quarks, covering multiple decay scenarios and providing new upper limits on these rare processes.

Findings

No significant excess observed above the Standard Model prediction.

Upper limits set on Higgs decay branching ratios into 4b and 6b final states.

Limits vary between 4% and 38% depending on scalar masses and decay modes.

Abstract

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, $H\rightarrow 2a \rightarrow 4b$, second to a pair of scalars with different masses ($m_{a1}<m_{a2}$), either directly, $H\rightarrow a_1a_2 \rightarrow 4b$, or via a longer decay chain, $H \rightarrow a_1a_2 \rightarrow 3a_1 \rightarrow 6b$. The analysis uses proton-proton collision data at $\sqrt{s} = 13$ TeV collected with the ATLAS detector at the Large Hadron Collider, corresponding to an integrated luminosity of $140~\mathrm{fb}^{-1}$. 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 $\sigma(ZH)/\sigma_{\text{SM}}(ZH) \times \mathcal{B}$($H \rightarrow 2a \rightarrow 4b$), between 24% and 38% for $\sigma(ZH)/\sigma_{\text{SM}}(ZH) \times \mathcal{B}$($H \rightarrow a_1a_2 \rightarrow 4b$), and between 10% and 20% for $\sigma(ZH)/\sigma_{\text{SM}}(ZH) \times \mathcal{B}$($H \rightarrow a_1a_2 \rightarrow 3a_1 \rightarrow 6b$), depending on the masses of the scalar particles.