The CLAS Cerenkov Detector

Nomenclature

There are at least four different numbering schemes for the PMTs in the Cerenkov detector. This is because the people who wrote the software for the readout did not communicate with the people who designed and built the detector. It would be very painful to resolve the different numbering schemes at this point, so we will instead document all of them here.

Construction scheme: Each of the sidewalls of the Cerenkov was constructed individually. The sidewalls themselves are identical; the two different sides are denoted "A" and "B" before any of the hardware is put on. Each sidewall has eighteen PMTs. Each PMT is labelled with its sector number, PMT number, and side (for example, CCS3 13B is sector 3, PMT 13B). There are two other schemes that are variations of this scheme, in which "A" and "B" become "L" and "R" (left and right) respectively, or "Lo Fi" and "Hi Fi" respectively. "Fi" is a misspelling of "phi", which denotes the azimuthal angle that the sidewall sits at.
Software scheme: In this scheme, the different phototubes are numbered so that as the number increases, the angle that the segment sits at increases monotonically. This means that each PMT is given a number from 1 to 36, and the sides alternate as the number increases.

Comparing the above schemes:

Construction scheme	Software scheme
CCS1 1A	CCS1 1
CCS1 1B	CCS1 2
...	...
CCS1 18A	CCS1 35
CCS1 18B	CCS1 36