Search for decays of stopped exotic long-lived particles produced in proton-proton collisions at $\sqrt{s}=$ 13 TeV

TL;DR

This paper reports a search for long-lived exotic particles that stop in the CMS detector and decay during quiet periods, setting new limits on their properties based on data from 2015-2016 at 13 TeV.

Contribution

First LHC search for stopped LLPs decaying into muons, with improved limits on hadronic decays, covering lifetimes from 100 ns to 10 days.

Findings

Set the most stringent limits on hadronically decaying stopped LLPs.

First LHC limits on LLP decays to muons.

Analyzed 38.6-39.0 fb$^{-1}$ of data from 2015-2016.

Abstract

A search is presented for the decays of heavy exotic long-lived particles (LLPs) that are produced in proton-proton collisions at a center-of-mass energy of 13 TeV at the CERN LHC and come to rest in the CMS detector. Their decays would be visible during periods of time well separated from proton-proton collisions. Two decay scenarios of stopped LLPs are explored: a hadronic decay detected in the calorimeter and a decay into muons detected in the muon system. The calorimeter (muon) search covers a period of sensitivity totaling 721 (744) hours in 38.6 (39.0) fb$^{-1}$ of data collected by the CMS detector in 2015 and 2016. The results are interpreted in several scenarios that predict LLPs. Production cross section limits are set as a function of the mean proper lifetime and the mass of the LLPs, for lifetimes between 100 ns and 10 days. These are the most stringent limits to date on the mass of hadronically decaying stopped LLPs, and this is the first search at the LHC for stopped LLPs that decay to muons.