Search for long-lived particles with displaced vertices in multijet events in proton-proton collisions at $\sqrt{s}=13~\mathrm{TeV}$

Results are reported from a search for long-lived exotic particles in proton-proton collision events at a center-of-mass energy of $\sqrt{s}=13~\mathrm{TeV}$ delivered by the CERN LHC and collected by the CMS experiment. The data sample, which was recorded during 2015 and 2016, corresponds to an integrated luminosity of $38.5~\mathrm{fb}^{-1}$. This search uses benchmark signal models in which long-lived exotic particles are pair produced and each decays into two or more quarks, leading to a signal with multiple jets and two displaced vertices composed of many tracks. No events with two well-separated high-track-multiplicity vertices are observed. Upper limits are placed on the pair production cross section as a function of mass and lifetime of the long-lived particle. For masses between 800 and $2600~\mathrm{GeV}$ and mean proper decay lengths between 1 and $40~\mathrm{mm}$, the analysis excludes cross sections above $0.3~\mathrm{fb}$ at $95\%$ confidence level. In models of $R$-parity violating supersymmetry in which the long-lived particles are gluinos decaying into multijet final states or top squarks decaying into dijet final states, gluino and top squark masses are excluded below $2200~\mathrm{GeV}$ and $1400~\mathrm{GeV}$, respectively, for mean proper decay lengths between 0.6 and $80~\mathrm{mm}$. The results are also applicable to other models in which pair-produced long-lived particles decay into final states with multiple tracks.