Difference of times of flight
Coinciding hits in a horizontal module and a vertical module
have been selected (as an example, North-South-24 and Up-Down-24
are shown below), and difference of time-of-flight for two planes
has been fitted. Time-of-flight for both planes was determined
from left-right half-sum of TDC times, and position is calculated
from half-difference. Three cuts on hit position were applied:
6cm (i.e., nominal intersection of 2 modules at their nominal
geographical location), 10cm (to accomodate for gaps/misalignment),
and 30cm. The best sigma of tTOF difference is 212 ps
which translates into about 150 ps per plane.
Time difference of 2 hits in the same event
This is a study of the idea to use 2 hits from the same
event to calibrate relative timing offsets of TOF modules
relative to each other. Here, tTOF of 2 hits
in modules NS20 and NS24 is compared. While mean value of
their relative time shift is only 63 ps (after cosmic calibration),
the RMS of the distribution is over 1.6 ns which may not
provide enough precision to do timing offset calibration.
Perhaps, extra cuts on tracks are needed to improve the width.
