Search for the Higgs boson produced in association with a $W$ boson and decaying to four $b$-quarks via two spin-zero particles in $pp$ collisions at 13 TeV with the ATLAS detector

Abstract

This paper presents a dedicated search for exotic decays of the Higgs boson to a pair of new spin-zero particles, $H\to aa$, 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 $\sqrt{s}=13$ TeV recorded in 2015 by the ATLAS detector at the CERN Large Hadron Collider, corresponding to an integrated luminosity of 3.2 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 $pp\to WH$ times the branching ratio for the decay $H\to aa\to 4b$. The upper limit ranges from 6.2 pb for an $a$-boson mass $m_a=20$ GeV to 1.5 pb for $m_a=60$ GeV.

26 pages plus author list (43 pages total), 7 figures, 3 tables, final version published in EPJC, All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HIGG-2016-01/

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