Search for long-lived particles in pp colision events with delayed trackless jets at sqrt(s) = 13 TeV

A search for long-lived particles decaying in the outer regions of the CMS silicon tracker or in the calorimeters is presented. The data sample consists of $138~\mathrm{fb}^{-1}$ of proton-proton collisions at $\sqrt{s} = 13~\mathrm{TeV}$, recorded at the LHC in 2016--2018. A novel technique, using trackless and delayed jet information combined in a deep neural network discriminator, is employed to identify decays of long-lived particles. The results are interpreted in a simplified model of chargino-neutralino production, where the neutralino is the next-to-lightest supersymmetric particle, is long-lived, and decays to a gravitino and either a Higgs or $\mathrm{Z}$ boson. This search is most sensitive to neutralino proper decay lengths of $\approx$1 $\mathrm{m}$, for which neutralino masses from up to 1180 $\mathrm{GeV}$ are excluded at $95\%$ confidence level.