ATLAS collaboration (2857 authors)Aguilar-Saavedra, Juan AntonioAmor Dos Santos, Susana PatriciaAnjos, NunoAraque, Juan PedroCarvalho, JoãoCastro, Nuno FilipeConde Muiño, PatriciaDa Cunha Sargedas De Sousa, Mario JoseFiolhais, MiguelGalhardo, BrunoGomes, AgostinhoGonçalo, RicardoJorge, PedroLopes, LourencoMachado Miguens, JoanaMaio, AméliaManeira, JoséOleiro Seabra, Luis FilipeOnofre, AntónioPedro, RuteSantos, HelenaSaraiva, JoãoSilva, JoséTavares Delgado, AdemarVeloso, FilipeWolters, Helmut2019-02-042019-02-042016-11-05http://dx.doi.org/10.1140/epjc/s10052-016-4418-9http://hdl.handle.net/10400.26/27130This paper presents a dedicated search for exotic decays of the Higgs boson to a pair of new spin-zero particles, $H \rightarrow aa$ , where the particle a decays to b-quarks and has a mass in the range of 20–60 GeV. The search is performed in events where the Higgs boson is produced in association with a $W$ boson, giving rise to a signature of a lepton (electron or muon), missing transverse momentum, and multiple jets from b-quark decays. The analysis is based on the full dataset of pp collisions at $\sqrt{s} = 13\,\mathrm{{TeV}}$ recorded in 2015 by the ATLAS detector at the CERN Large Hadron Collider, corresponding to an integrated luminosity of 3.2 $\text{ fb }^{-1}$ . No significant excess of events above the Standard Model prediction is observed, and a $95\,\%$ confidence-level upper limit is derived for the product of the production cross section for $pp \rightarrow WH$ times the branching ratio for the decay $H \rightarrow aa \rightarrow 4b$ . The upper limit ranges from 6.2 pb for an a-boson mass $m_a = 20\,\mathrm{{GeV}}$ to 1.5 pb for $m_a = 60\,\mathrm{{GeV}}$ .engjournal article2019-02-04