Alignment of the ALEPH silicon vertex detector

The ALEPH silicon vertex detector consists of 96 silicon wafers, arranged in two concentric cylinders around the Large Electron-Position Collider (LEP) interaction joint. Each wafer is read out in two perpendicular directions, with a resolution of approximately 10 mu m in each. The authors describe the techniques used to align the wafers to the accuracy needed to exploit this resolution. The alignment starts with an optical measurement of the relative wafer positions. The wafers are then positioned with data from e/sup +/e/sup -/ collisions, using several redundant constraint techniques. The final vertex detector alignment is then propagated back to realign the outer tracking devices. These techniques were used to align the detectors currently operating in ALEPH with estimated errors of 3(+)3 mu m in the R- phi direction, and 8(+) mu m in the Z direction (statistical (+) systematic errors).<>