Search for Higgs boson decays into two new low-mass spin-0 particles in the 4$b$ channel with the ATLAS detector using $pp$ collisions at $\sqrt{s}=13$ TeV

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, $H\to aa\to (b\bar{b})(b\bar{b})$, 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 $15\le m_a\le 30$ 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 $20\le m_a\le 60$ GeV. A novel strategy for the identification of the $a\to b\bar{b}$ 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 $H\to aa\to (b\bar{b})(b\bar{b})$, where the Higgs boson is produced in association with a $Z$ boson.

40 pages in total, author list starting page 24, 10 figures, 2 table, published by Phys.Rev.D. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HDBS-2018-47/

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