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,text {fb}^text {-1} of 8,text {TeV} proton–proton collisions, and a search interval corresponding to 281 h 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 lesssim 1000,text {GeV} and a top squark with mass lesssim 525,text {GeV} are excluded, for lifetimes between 1 upmu s and 1000text {s}. These results are the most stringent constraints on stopped particles to date.
Highlights
Many extensions of the standard model (SM) predict the existence of new heavy long-lived particles [1,2,3,4,5,6]
These searches are complemented by those that target the fraction of such particles produced with sufficiently low kinetic energy (KE) that they come to rest in the detectors
Since these depositions might be difficult to differentiate from those of SM particles produced in pp collisions, they would be most observed at times between pp collisions
Summary
Many extensions of the standard model (SM) predict the existence of new heavy long-lived particles [1,2,3,4,5,6]. At the CERN LHC the two general-purpose detectors, ATLAS and CMS, have already set stringent limits on the existence of such particles with searches that exploit the anomalously large ionization and/or long time-of-flight that they would exhibit as they traverse the detectors [7,8]. These searches are complemented by those that target the fraction of such particles produced with sufficiently low kinetic energy (KE) that they come to rest in the detectors. The new analysis benefits from a fourfold integrated luminosity increase and uses data resulting from higher energy pp collisions compared to the previous CMS publication [14]
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