  A search for long-lived particles (LLPs) produced in decays of standard model
(SM) Higgs bosons is presented. The data sample consists of 137 fb$^{-1}$ of
proton-proton collisions at $\sqrt{s} =$ 13 TeV, recorded at the LHC in
2016-2018. A novel technique is employed to reconstruct decays of LLPs in the
endcap muon detectors. The search is sensitive to a broad range of LLP decay
modes and to masses as low as a few GeV. No excess of events above the SM
background is observed. The most stringent limits to date on the branching
fraction of the Higgs boson to LLPs subsequently decaying to quarks and
$\tau^+\tau^-$ are found for proper decay lengths greater than 6, 20, and 40 m,
for LLP masses of 7, 15, and 40 GeV, respectively.
