Test beam measurement of the detection efficiency of ATLAS Pixel production modules

Beam tests of ATLAS Pixel Detector production modules were performed with a pion beam at the SPS H8 test beam facility. Several of the modules had been previously irradiated with protons to a fluence of 2 * 10**15 p/cm2, corresponding to 10**15 neq/cm2. This note presents measurements of detection efficiency performed in 2004 on one not irradiated and seven irradiated modules. The efficiency was studied as a function of the operating bias voltage and for different incidence angles. The unirradiated module has an extremely good detection efficiency. A value of 99.9 % was measured at normal incidence. Irradiated detectors have an average efficiency of 97.8 % at the standard operating bias voltage of 600 V. The timing uniformity across the different types of pixel cells (standard, long and ganged pixels) and between the sixteen front-end readout chips was also studied and found to be better than 2 ns. The effects of hit duplication on the detection efficiency, the spatial resolution and the pixel occupancy were also studied.