The cathode read-out of the DELPHI hadron calorimeter

To improve the identification and separation of leptons in the hadron calorimeter of DELPHI, one of the four LEP experiments at CERN, the possibility of a direct read-out of the cathodes of the 20,000 limited streamer tubes was studied and successfully tested on a small scale. A larger scale test started in June 1994. This new system which is independent of the present pad read-out provides a “yes/no” information. The combination of both read-out systems makes it possible to use the hadron calorimeter as a track detector. The result of these tests show that the cathode read-out provides a better π/μ separation, and improved detection of neutral long lived particles, enhanced discrimination of two showers and a more precise hadron energy measurement. It was decided to equip the whole detector with the new read-out, starting during the 94/95 shutdown