Search for triple Higgs boson production in the $ 6b$ final state using $ pp$ collisions at $ \sqrt{s}=13\text{}\text{}\mathrm{TeV}$ with the ATLAS detector

A search for the production of three Higgs bosons ($ HHH$) in the $ b\overline{b}b\overline{b}b\overline{b}$ final state is presented. The search uses $ 126\text{}\text{}{\mathrm{fb}}^{-1}$ of proton-proton collision data at $ \sqrt{s}=13\text{}\text{}\mathrm{TeV}$ collected with the ATLAS detector at the Large Hadron Collider. The analysis targets both nonresonant and resonant production of $ HHH$. The resonant interpretations primarily consider a cascade decay topology of $ X\to SH\to HHH$ with masses of the new scalars $ X$ and $ S$ up to 1.5 and 1 TeV, respectively. In addition to scenarios where $ S$ is off-shell, the nonresonant interpretation includes a search for Standard Model $ HHH$ production, with limits on the trilinear and quartic Higgs self-coupling set. No evidence for $ HHH$ production is observed. An upper limit of 59 fb is set, at the 95% confidence level, on the cross section for Standard Model $ HHH$ production.