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

TL;DR

This paper reports a search for exotic Higgs decays into pairs of low-mass spin-0 particles decaying into b-quark pairs, using ATLAS data at 13 TeV, employing a novel identification method for collimated decay products.

Contribution

Introduces a new strategy for identifying collimated $a ightarrow bar{b}$ decays in Higgs to four b-quark final states at the LHC.

Findings

Sets upper limits on the cross-section for $H ightarrow aa ightarrow (bar{b})(bar{b})$

Focuses on the low-mass regime $15 ext{ to } 30$ GeV for the new particles

Employs a novel identification technique for collimated decay products

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.