ATLAS Pixel Detector System Test

Abstract

On June 25th of 2007 the ATLAS collaboration lowered the pixel detector into place, however before this the detector had to be qualified through a series of tests. Prior to assembly, each individual piece of the detector and services chain passed a set of quality controls. This was followed by the construction and test of the whole pixel detector. This test of the full chain of services -including the voltage supplies, opto-boards, cooling, temperature monitoring, control software, and the pixel modules themselvesis referred to as the Pixel System Test. The System Test took place in an above-ground laboratory setting at CERN and consisted of two main parts. The first half of the test focused on one of the pixel detector’s endcaps. This endcap consists of 144 modules, making up roughly 10% of the total pixel detector. For the pixel endcap test, most of the 144 modules were operated simultaneously which required that the pixel endcap’s cooling system be functioning as well[1]. Additionally, four scintillators were added above and below the detector which trigged on cosmic muons. As a result, the pixel detector measured its first cosmic tracks during this test. After the cosmic test the pixel collaboration connected the entire pixel detector a few modules at a time. The cooling for the pixel detector could not be used in this setting, and to prevent overheating any componants only one chip was powered on at a time. This half of the system test is referred to as the connectivity test[3]. I. THE PIXEL DETECTOR The ATLAS pixel detector has a strict set of design requirements. First, due to its proximity to the beam pipe, it must be able to operate under a lifetime dose of radiation of at least 50 Mrad. Second, in order to perform B-tagging, the detector needs a high resolution in ηφ which translates into a requirement for a high granularity and low mass pixel detector. With its 80 million pixel channels in three concentric layers covering a total of 1.8m and mass of 0.10χ0, the ATLAS pixel detector achieves an impact resolution of 12μm. Finally, the high rate of bunch crossings and slow trigger latency mean that the pixel detector must store the hits from 100 beam crossings in each on chip buffer and distinguish which of those hits pertain to each bunch