The calorimeter is capable of a very precise measurement of the time of the energy deposit with a resolution in the nanosecond range. Since the dimensions of the calorimeter are in orders of meters it is possible to use the time information to calculate the velocity of the traversing muon.
The candidate velocity is then calculated through a weighted linear regression fit using the position of each cell along the fitted line and the cell time. The cell time is in addition corrected for the distance of the cell center from the line. The weight is calculated using the prescription explained in [18].
Even though the velocity of a candidate seems like a good identification tool it should only be used with care: An event with a prompt muon and opposing it some very low energy deposit might result in a muon candidate with a velocity close to the speed of light because the low energy deposit might not contribute enough to the linear regression line fit.
Figure 6.9 shows a histogram of the velocity for all positively identified muon candidates, the histogram is restricted to ( ) but only of the candidates have a velocity outside the shown region. The mean value of the distribution is at which is very close to the speed of light indicating that indeed the observed signal stems from highly energetic particles traversing the detector.