ATLAS Collab.
Search for Higgs boson decays into two new low-mass spin-0 particles in the 4b channel with the ATLAS detector using pp collisions at √s=13 TeV
This paper describes a search for beyond the Standard Model decays of the Higgs boson into a pair of new spin-0 particles subsequently decaying into b-quark pairs, H→aa→(bb)(bb), using proton-proton collision data collected by the ATLAS detector at the Large Hadron Collider at center-of-mass energy √s=13 TeV. This search focuses on the regime where the decay products are collimated and in the range 15≤ma≤30 GeV and is complementary to a previous search in the same final state targeting the regime where the decay products are well separated and in the range 20≤ma≤60 GeV. A novel strategy for the identification of the a→bb decays is deployed to enhance the efficiency for topologies with small separation angles. The search is performed with 36 fb−1 of integrated luminosity collected in 2015 and 2016 and sets upper limits on the production cross-section of H→aa→(bb)(bb), where the Higgs boson is produced in association with a Z boson.