Search for the Higgs boson produced in association with a vector boson and decaying into two spin-zero particles in the $H \rightarrow aa \rightarrow 4b$ channel in $pp$ collisions at $\sqrt{s} = 13$ TeV with the ATLAS detector

Understand

A search for exotic decays of the Higgs boson into a pair of spin-zero particles, $H \rightarrow aa$, where the $a$-boson decays into $b$-quarks promptly or with a mean proper lifetime $c\tau_a$ up to 6 mm and has a mass in the range of $20-60$ GeV, is presented.

• The search is performed in events where the Higgs boson is produced in association with a $W$ or $Z$ boson, giving rise to a signature of one or two charged leptons (electrons or muons) and multiple jets from $b$-quark decays.
• The analysis is based on the dataset of proton-proton collisions at $\sqrt{s} = 13$ TeV recorded in 2015 and 2016 by the ATLAS detector at the CERN Large Hadron Collider, corresponding to an integrated luminosity of 36.1 fb$^{-1}$.
• No significant excess of events above the Standard Model background prediction is observed, and 95% confidence-level upper limits are derived for the production cross-sections for $pp \rightarrow WH$, $ZH$ and their combination, times the branching ratio of the decay chain $H \rightarrow aa \rightarrow 4b$.