in any given event is the calorimetric missing transverse energy [@cite:cmsMETnote].

The missing transverse energy (MET) is reconstructed from calorimeter towers, which are reconstructed objects containing the sum of the signals from HCAL and ECAL cells at the same $(\eta,\phi)$ coordinates. The MET is calculated by taking the magnitude of the vector sum of the transverse energy contributions of towers,

$$\label{eq:met}
MET = \sqrt{(\sum_\mathrm{towers}E_i\sin\theta_i\cos\phi_i)^2 + (\sum_\mathrm{towers}E_i\sin\theta_i\sin\phi_i)^2}\quad,$$

where $E_i$ and $(\theta_i,\phi_i)$ are the energy and angle coordinates of each tower.

Multiple complications arise in the accurate measurement of MET. The energies of jets or leptons can be mismeasured due to detector miscalibration or shower fluctuations in the dead material of the detector. The MET in a collision event can also be affected by energy deposits in HCAL cells from non-collision sources. Without a separate identification of these sources the energy will be misassigned to the event of interest, inducing fake MET. Example sources include cosmic ray muons, detector noise, and beam halo.

This section explores the use of HCAL timing as a potential tool to identify sources of fake MET. The CMS design ensures that the phase of collision products relative to the LHC clock is fixed to high precision. The 