Log entry time 14:05:38 on February 21, 2011

Entry number 221313

This entry is a followup to: 221289

We can ignore detector signal cable tempcos for our CM signals, but not the PMT gain tempco's since they are of order 1%/C. Since most electronics achieve tempcos of 0.1%/C or better, the PMTs are usually the least stable element in the system. Our PMTs are buffered from drafts being buried inside the detector modules, but we still expect to see a phase-shifted remnant of the multi-hour cycling of the air handling system SAW showed in

https://hallcweb.jlab.org/hclog/1102_archive/110219061553.html

In Figure 4 of the attached reference I grabbed online, they measured a gain tempco of about -.7%/C at temperature, but exhibiting a range of personalities. Our results may vary due to different materials and preparation. The lumis derive no gain from their dynodes, so their tempcos could be quite different.

In Juliette's MD7 yield vs time plot I see a total variation of +-0.7% which is good performance if we still have those +-2C temperature variations every 2 hours. One reason we're having this discussion is that not so long ago the temperature variations in the hall were only +-1C. (The other reason of course is that Juliette got game.) The PMT tempco is one reason the CM yield measurements vs QTOR current or beam current should be done quickly, and why repeated measurements are needed to estimate random errors.

Figure 1