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

TL;DR

This paper reports a search for long-lived particles decaying into multiple jets with displaced vertices in proton-proton collisions at 13 TeV, setting new limits on certain supersymmetric models and providing a method to extend these results.

Contribution

It introduces a search strategy for long-lived particles with displaced vertices and sets new exclusion limits for specific supersymmetric models at the LHC.

Findings

No events with two displaced vertices were observed.

Excluded cross sections above 0.3 fb for certain mass and decay length ranges.

Gluino and top squark masses below 2200 and 1400 GeV are excluded for specific decay lengths.

Abstract

Results are reported from a search for long-lived particles in proton-proton collisions at $\sqrt{s} =$ 13 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 fb$^{-1}$. This search uses benchmark signal models in which long-lived 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 models of $R$-parity violating supersymmetry in which the long-lived particles are neutralinos or gluinos decaying solely into multijet final states or top squarks decaying solely into dijet final states. For neutralino, gluino, or top squark masses between 800 and 2600 GeV and mean proper decay lengths between 1 and 40 mm, the analysis excludes cross sections above 0.3 fb at 95% confidence level. Gluino and top squark masses are excluded below 2200 and 1400 GeV, respectively, for mean proper decay lengths between 0.6 and 80 mm. A method is provided for extending the results to other models with pair-produced long-lived particles.