A new technique for charge dependent corrections to the time response of the drift tubes of the ATLAS experiment

Monitored Drift Tubes (MDT), filled with a mixture of Ar : CO₂ at 3 bar pressure, are used as tracking devices for the ATLAS muon spectrometer at the Large Hadron Collider. The MDT chamber tested is equipped with the final version of front-end electronics, which provides information about the collected charge through a Wilkinson ADC. We present an analysis of the signal and timing characteristics, and of charge-dependent time response of the MDTs. A new method to improve the spatial resolution of MDT chambers using the ADC information to correct the time response was developed. The procedure is based solely on the data from the MDT chamber itself. The improvement with respect to previous methods is achieved thanks to an indirect derivation of the slope of the induced anode signal. This requires an accurate determination of the response function of the ADC. Response function which is obtained by injection pulse of known charge in the integrator circuit. The method is validated with a simulation of the tube response with the Garfield program.