  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.
