Tests of full-scale Pixel HPD prototype

The performance of prototype Hybrid Photo-Diodes (HPDs) with 80 mm diameter is evaluated, anticipating their usage in the RICH detectors of the LHCb experiment at CERN. Data from LED scan are used to estimate the magnitude of demagnification from cross- focusing. The photoelectron yields and Cherenkov angle resolutions obtained from these HPDs when used as part of a RICH detector installed in a test beam have been measured. The results agree with the expectations from simulations. The response of these tubes to charged particles is also reported.