Search for b hadron decays to long-lived particles in the CMS endcap muon detectors

A search for long-lived particles originating from the decay of b hadrons produced in proton-proton collisions with a center-of-mass energy of 13 TeV at the LHC is presented. The analysis is performed on a data set recorded in 2018, corresponding to an integrated luminosity of 41.6 fb${}^{-1}$. Interactions of the long-lived particles in the CMS endcap muon system would create hadronic or electromagnetic showers, producing clusters of detector hits. Selected events contain at least one such high-multiplicity cluster in the muon endcaps and require the presence of a displaced muon. The most stringent upper limits to date on the branching fraction $\mathcal{B}$(B $\to$ K$\mathrm{\Phi }$), where the long-lived particle $\mathrm{\Phi }$ decays to a pair of hadrons, are obtained for $\mathrm{\Phi }$ masses of 0.3$-$3.0 GeV and $\mathrm{\Phi }$ mean proper decay lengths in the range of 1$-$500 cm.