Search for Higgs boson decays into a pair of pseudoscalar particles in the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>b</mml:mi><mml:mi>b</mml:mi><mml:mi>μ</mml:mi><mml:mi>μ</mml:mi></mml:math> final state with the ATLAS detector in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>p</mml:mi><mml:mi>p</mml:mi></mml:math> collisions at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msqrt><mml:mi>s</mml:mi></mml:msqrt><mml:mo>=</mml:mo><mml:mn>13</mml:mn><mml:mtext> </mml:mtext><mml:mtext> </mml:mtext><mml:mi>TeV</mml:mi></mml:math>

This paper presents a search for decays of the Higgs boson with a mass of 125 GeV into a pair of new pseudoscalar particles, $H\ensuremath{\rightarrow}aa$, where one $a$-boson decays into a $b$-quark pair and the other into a muon pair. The search uses $139\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of proton-proton collision data at a center-of-mass energy of $\sqrt{s}=13\text{ }\text{ }\mathrm{TeV}$ recorded between 2015 and 2018 by the ATLAS experiment at the LHC. A narrow dimuon resonance is searched for in the invariant mass spectrum between 16 GeV and 62 GeV. The largest excess of events above the Standard Model backgrounds is observed at a dimuon invariant mass of 52 GeV and corresponds to a local (global) significance of $3.3\ensuremath{\sigma}$ ($1.7\ensuremath{\sigma}$). Upper limits at 95% confidence level are placed on the branching ratio of the Higgs boson to the $bb\ensuremath{\mu}\ensuremath{\mu}$ final state, $\mathcal{B}(H\ensuremath{\rightarrow}aa\ensuremath{\rightarrow}bb\ensuremath{\mu}\ensuremath{\mu})$, and are in the range $0.2--4.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$, depending on the signal mass hypothesis.

Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.