Search for massive long-lived particles decaying semileptonically at √s=13TeV

A search is performed for massive long-lived particles (LLPs) decaying semileptonically into a muon and two quarks. Two kinds of LLP production processes were considered. In the first, a Higgs-like boson with mass from 30 to 200\,GeV\!/ c² is produced by gluon fusion and decays into two LLPs. The analysis covers LLP mass values from 10\,GeV\!/ c² up to about one half the Higgs-like boson mass. The second LLP production mode is directly from quark interactions, with LLP masses from 10 to 90\,GeV\!/ c². The LLP lifetimes considered range from 5 to 200 ps. This study uses LHCb data collected from proton-proton collisions at s=13\,TeV, corresponding to an integrated luminosity of 5.4\,fb ^{- 1}. No evidence of these long-lived states has been observed, and upper limits on the production cross-section times branching ratio have been set for each model considered.