Performance of an artificially aged module of the DELPHI HPC calorimeter

The readout proportional chambers of the HPC electromagnetic calorimeter in the DELPHI experiment are affected by large ageing. In order to study the calorimeter long-term behaviour, one HPC module was extracted from DELPHI in 1992 and was brought to a test area where it was artificially aged during a period of two years; an ageing level exceeding that expected for the HPC at the end of the LEP era was reached. During this period the performance of the module was periodically tested by means of dedicated beam tests whose results are discussed in this paper. These show that ageing has no significant effects on the response linearity and on the energy resolution for electromagnetic showers, once the analog response loss is compensated for by increasing the chamber gain through the anode voltage.