[Clas12_rgb] problem (and fix) with FC for spring runs

silvia at jlab.org silvia at jlab.org
Thu Aug 27 04:49:58 EDT 2020


Dear all,
I ran the QA timelines on the spring cooked data, and noticed a strange
change in the normalized electron yields, corresponding to a change of
slope in the integrated charge, for the runs before/after 6400.
Digging more, I found that this is due to an issue with the latest update
before our cooking in CCDB: the attenuation (the "atten" parameter) for
the Faraday cup was set to "1" for the runs before 6400 (which marks the
start of the 10.2 GeV set) instead of the correct value (9.96025).
Therefore, the FC charge for the runs < 6400 is smaller than the actual
value by 9.96025, as atten is used as a scaling factor at the decoding
stage.
If you are currently using, or planning to use, the FC charge in your
analysis, make sure to account for this (something along the lines of "if
run <6400 fc = 9.96025*fc").
I have discussed the issue with Raffaella, she says that later on we can
se if this can be corrected in post-processing, redoing the trains or the
like.
But for the time being, please correct "by hand" in your analysis.
Apologies for the issue, I should have checked better before these infos
were uploaded in CCDB.
Best regards,
Silvia




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