Function Time to Distance Conversion

Drift time to distance can be well described by the formula


Where c0 is the half width of the drift chamber cell (0.5cm for GEn), v is the constant drift velocity at low drift times (on the order of 5x10^-5 m/ns), and t0 is a global TDC offset.

c2 is a constant that describes the "transition region" in the drift time spectrum where the drift time to distance conversion changes from a constant velocity at low drift times to an asymptotic approach to a constant drift distance (the half cell width).

Calibration

Attached is a script that calculates these values from a replay. This replay requires that there be no cuts in drift time done (so drift.min and drift.max in db_B.dc.dat should be set to very low and high values). This is required to remove the large background contributions. Also, tracking should be disabled for this type of run so it does not become overwhelmed with the large number of drift chamber hits.

This script should not be run blindly and will not run without adding in parameters such as the ROOT file path, number of drift planes, etc. There is a number of defined values that are required and can be found in a mwdc_defs.h header. (See BigBite Analysis Scripts for a copy)

The output to stdout is identical to that required in db_B.dc.dat using the THaVDCFuncTTDConv class.