Search for long-lived particles using out-of-time trackless jets in proton-proton collisions at √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 search is based on a data sample of proton-proton collisions at root s = 13TeV recorded with the CMS detector at the LHC in 2016-2018, corresponding to an integrated luminosity of 138 fb(-1). A novel technique, using nearly trackless and out-of-time 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 Z boson. This search is most sensitive to neutralino proper decay lengths of approximately 0.5 m, for which masses up to 1.18TeV are excluded at 95% confidence level. The current search is the best result to date in the mass range from the kinematic limit imposed by the Higgs boson mass up to 1.8TeV.

Automated summary

This study presents a search for long-lived particles decaying in the outer regions of the CMS silicon tracker or in the calorimeters. The search is conducted using a novel technique that combines trackless and out-of-time jet information in a deep neural network discriminator. The results provide insights into the decay lengths and mass ranges of neutralino particles.