SHARC Coordinate System
This is a brief explanation of the SHARC coordinate system. If this confuses you (which is will if you're anything like me) or you notice a mistake, please tell me (Phil Adsley: e-mail pa541 at york.ac.uk or padsley at gmail) and I'll be very happy to try to help. Many thanks to Greg and Christian for trying, a number of times, to explain this to me in the first place. I hope that I haven't messed it up too much... Apologies for the drawings, I hope they're ok for the moment, I will change them for something done on computers and all fancy and clear when I have time.
If you're in Vancouver, the best thing to do is to find Gemma's models of SHARC which reside currently in the TIGRESS counting room. These show the general directions and the detector positions so that you can orientate yourself. They're also much clearer than this description...
The SHARC coordinate system works in the same way to the TIGRESS coordinate system. θ = 0 is downstream, φ = 0 is north ('beam' left, that is, left according to the beam as it travels through the chamber) and z = 0 is at the target position. On TIGRESS, the number of the detectors increases with φ as you move from φ = 0 to φ = 2π. The 'first' detector in each ring is the first one that you 'hit' as you move around from φ = 0 and each time you 'hit' a new detector in that ring, you increase you count by one. This is summarised in the diagram below (Figure 1).
SHARC works in the same way. We start at φ = 0 and start counting the numbers of detectors and brackets when we 'hit' them moving around from φ = 0. So, as can be seen in the figure below, the first bracket that we hit it BRACKET 1 and it is the one on the UPPER and NORTH side of the beam, above the target mechanism. The first box detector hit is the one above the beam; UBx1 and DBx1 are thus the detectors above the beam. Bx2s are on the south side; beam right. Bx3s are below the beam. Bx4s are on the north side by the target mechanism and are beam left. CDs are labelled according to the bracket which they sit above.