Abstract
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, $H \rightarrow aa \rightarrow (b\bar{b})(b\bar{b})$, using proton-proton collision data collected by the ATLAS detector at the Large Hadron Collider at center-of-mass energy $\sqrt{s}=13$ TeV. This search focuses on the regime where the decay products are collimated and in the range $15 \leq m_a \leq 30$ 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 $20 \leq m_a \leq 60$ GeV. A novel strategy for the identification of the $a \rightarrow b\bar{b}$ 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 $H \rightarrow aa \rightarrow (b\bar{b})(b\bar{b})$, where the Higgs boson is produced in association with a $Z$ boson.
Highlights
The Higgs boson is a particle with a narrow natural width, and its branching fractions to new light particles can be sizable even if they interact weakly with it
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 → ðbb Þðbb Þ, using protonproton cpolffilffiision data collected by the ATLAS detector at the Large Hadron Collider at center-of-mass energy s 1⁄4 13 TeV
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 → ðbb Þðbb Þ, where the Higgs boson is produced in association with a Z boson
Summary
The Higgs boson is a particle with a narrow natural width, and its branching fractions to new light particles can be sizable even if they interact weakly with it. Several new weakly interacting light particles that would not be visible in inclusive searches can be probed by searching for “beyond the Standard Model” (BSM) Higgs boson decays at the LHC [1]. These new light particles are predicted in several BSM theories with extended Higgs sectors [2,3,4,5,6] that address open questions in high-energy physics.
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