four time samples considered in the reconstruction of an HCAL measurement. The fake MET production for all three samples is due predominantly to a small number of high energy measurements, against which the filter is most effective.

The filter can be tuned to enhance further the background rejection performance. More sophisticated algorithms could be employed to filter clusters of cells with mixed in-time and out-of-time signals if the members of the cluster share common characteristics that identify them as background. For instance, beam halo muons may create a cluster of deposits in consecutive cells along $\eta$ for the same $\phi$, most of which will be out-of-time. This pattern, once identified, could allow the removal of nominally in-time background as well.

Impact on physics processes
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To estimate the impact of this technique on signals that have not yet been produced in the CMS detector, studies have been performed on two simulated processes, one that contains MET at the event generator level and a second that does not. An interesting example of the first case is the real MET induced by the hypothetical weakly-interacting supersymmetric (SUSY) [@cite:susy] particle called the neutralino. By applying an ill-chosen time filter, one may underestimate the 