Summary

A method to measure the efficiency in all chambers of the Inner Tracker is described. This method has been applied to real and simulated data. Possible sources of bias to the estimated efficiency numbers have been investigated and found to be small. The only problem not accounted completely for is the bias introduced by dead strips remaining after masking. It can be seen from the large efficiency deviation for chambers with a very large number of non working channels.

The measured average efficiencies for chambers which were not re-equipped during the shutdown in 2001 vary between 90% and 95%. For chambers equipped with the new version of Helix the efficiency is between 50% and 90%. These numbers are significantly below the expected efficiency of 95% (this low efficiency seriously affects the track reconstruction efficiency of the Inner Tracker system). In principle the hit efficiency of several chambers can be improved by adjusting GEM voltages. However this is limited by the required operational stability of those chambers.