Building a Stereo-angle into strip-sensors for the ATLAS-Upgrade Inner-Tracker Endcaps

The Strips Endcap detector for the ATLAS Upgrade needs several sensor shapes, each of which is approximately a wedge shape like the current SCT. For the Endcap to use a stave-like approach as proposed for the barrel, care is needed to design the shapes to avoid clashes and minimise gaps between them. This note gives the basic formulae for one way of building up a petal. It allows for a stereo-angle to be built into the wafer, and takes into account the maximum usable wafer size.