Quality tests of the LHCb muon chambers at the LNF production site

The performance demanded for the Level-0 trigger of LHCb imposes very stringent requirements on the quality of the muon chambers. These chambers must pass a series of tests before being mounted in the experimental setup. The six tests adopted for the quality control of the chambers produced at the Laboratori Nazionali di Frascati (LNF) are described. After the wires are wound and glued on a cathode panel, the wire pitch is measured by two digital cameras with a precision of about 20 pm. The mechanical tension of the wire is deduced from its mechanical resonance frequency measured by an automated system based on a digital electrostatic method. The wire tension is obtained with a precision of about 1%. Once all elements are assembled, the gas tightness of a chamber is verified by monitoring the decrease rate of an over-pressure applied to it. After a suitable high-voltage conditioning, the dark current is recorded and the gas gain uniformity of the chamber is measured using a collimated Cs-137 source which can be moved over the chamber surface. Finally, the detector is fully equipped with the front-end electronics, and its detection efficiency is tested with cosmic rays.