Search for decays of stopped long-lived particles produced in proton-proton collisions at sqrt(s) = 8 TeV

TL;DR

This paper reports a search for long-lived particles that stop within the CMS detector and decay at delayed times, setting new limits on gluino and top squark production over a wide lifetime range.

Contribution

It introduces a novel search method for stopped long-lived particles using timing information, providing the most stringent constraints to date.

Findings

No significant excess observed over background.

Excluded gluino masses below 1000 GeV for certain lifetimes.

Excluded top squark masses below 525 GeV for certain lifetimes.

Abstract

A search has been performed for long-lived particles that could have come to rest within the CMS detector, using the time intervals between LHC beam crossings. The existence of such particles could be deduced from observation of their decays via energy deposits in the CMS calorimeter appearing at times that are well separated from any proton-proton collisions. Using a data set corresponding to an integrated luminosity of 18.6 inverse femtobarns of 8 TeV proton-proton collisions, and a search interval corresponding to 281 hours of trigger livetime, 10 events are observed, with a background prediction of 13.2 +3.6 -2.5 events. Limits are presented at 95% confidence level on gluino and top squark production, for over 13 orders of magnitude in the mean proper lifetime of the stopped particle. Assuming a cloud model of R-hadron interactions, a gluino with mass < 1000 GeV and a top squark with mass < 525 GeV are excluded, for lifetimes between 1 microsecond and 1000 s. These results are the most stringent constraints on stopped particles to date.