a single muon is identified by the CMS muon stations. The beam events were taken with a single circulating 450 proton bunch on September 18, 2008. All events from this sample are included in the plots regardless of trigger source, which could be beam pickup, coincidence of scintillator or forward calorimeter energy deposits, or any of several muon triggers. The beam sample thus includes beam halo and beam-gas events as well as cosmic ray muons and accidental overlaps with calorimeter noise events. In all cases, the physical MET value would be zero, so a net migration of events from high MET to low MET is expected when comparing the unfiltered and time-filtered MET distributions.

Figure \[fig:bkgdMETplots\] also shows the fraction of events that survive a minimum MET criterion as a function of the threshold value. This was done for both the time-filtered and unfiltered distributions for each background type. Figure \[fig:bkgdMETplots\], therefore, indicates that a reduction by a factor of 5–10 in the rate of events with fake MET can be achieved with time filtering for all three sources of background studied. This rejection factor is consistent with the ratio of the filter window width to the width of the 