the timing filter was then applied to two datasets: beam background data collected during LHC beam commissioning in September 2008 and cosmic ray muon and CMS detector noise background data collected in October and November 2008, during the month-long data-taking exercise known as the Cosmic Run At Four Tesla (CRAFT) [@cite:CRAFTGeneral]. For each event, the MET was calculated twice for comparison. One calculation of MET used all energy deposits (referred to as “unfiltered”), while the second did not include energy deposits with a measured time outside the window (referred to as “time-filtered”). The unfiltered measurements include energy depositions in bunch crossings other than the triggered one, as a consequence of the triggering and reconstruction algorithms used during these periods.

The comparison between the unfiltered MET and the time-filtered MET for HCAL-triggered events, cosmic ray events, and beam events is shown in Fig. \[fig:bkgdMETplots\]. The HCAL-triggered events were collected using a Level-1 trigger in which a single calorimetric tower energy exceeds a 5 threshold. Therefore, this sample includes photo-detector and other instrumental noise events [@cite:anomevents]. Events with a Level-1 muon trigger were removed from the sample. The cosmic ray muon events were collected during CRAFT with a Level-1 trigger in which 