Drift Chamber (DC) Calibration

Calibration of the drift chamber involved finding the drift velocity of electrons in the drift chamber gas as well as the set of time pedestals for each of the 1632 drift chamber wires. This was done following the procedure as detailed in Reference (26).

To find the accurate time pedestal for each of the 1632 drift chamber wires, an iterative technique was used. Beginning with a reasonably guessed drift velocity, an initial estimate was obtained after several iterations of the drift time pedestals. Subsequently, the $\chi ^2$ of the fitted tracks was calculated corresponding to several drift velocities above and below the estimated one, and the drift velocity corresponding to the minimum $\chi ^2$, and therefore the best fit, was selected as the effective velocity of the drift electrons in the drift chamber. Next, a final set of 1632 time pedestals were calculated by repeating this iteration process with this new drift velocity. Since run conditions such as the exact composition of the drift chamber gas etc. were subject to slight variations from one running period to another, the drift chamber calibration was done using the same technique as described below for each of the running periods listed in Table 3.1.