During Run 20, we experienced a problem with delivering power to two RDOs in Sector 13: both TPX RDO 3 (rows 41-48) and TPX RDO 6 (rows 65-72) were on a single power supply. Tonko indicated the possibility of restoring one of the two RDOs, and that it may be just as possible to restore either one. That made me wonder if one was a better choice to restore than the other.

I processed 2000 events from run 21029051, from before the problems supplying power to the two RDOs, in four configurations:

1. both RDOs enabled
2. RDO 3 manually disabled
3. RDO 6 manually disabled
4. both RDOs manually disabled

One can see that I successfully disabled these RDOs in these plots from Offline QA of the TPC hits:

[sidenotes: (1) I did not inform Sti of the dead rows, which should be done to help tracking cross the dead regions; (2) TPX RDOs 3-6 are the 5^th through 8^th RDOs in the TPC, and are labeled 5 and 8 in the below plots]



I then did track-by-track comparisons of Δ(q/p_T) vs. q*p_T for each of the three disabled scenarios against the reference of having both RDOs enable. These are shown below, using "profs" to obtain error bars that represent the spread in values (not the error on the mean).



These plots show that having RDO 6 absent causes more spread, or more alteration of the originally reconstructed momentum, than does having RDO 3 absent.

This makes sense in light of the track momentum resolution being dependent on both the track length as well as the number of hits on the track. The number of hits may be largely unaffected by having one or the other of these two RDOs disabled, but the length is more notably affected by the absence of RDO 6, arguing in favor of making an effort to re-enable RDO 6 over RDO 3.

A caveat to this finding is that if TPC hits on the outermost rows (TPC RDO 6) are less-well-calibrated than those in the middled (TPX RDO 3), then the presence or absence of the poorly calibrated hits can lead to alteration of the track momentum as well, in which case one is better off without the less-well-calibrated hits in tracking. There is some reason to believe this is a possibility as there are hints of non-zero, but small SpaceCharge in the east TPC where Sector 13 sits, and that would create more distortion at the outer TPC than the middle. But in hopes that the TPC is well-calibrated for the final production, I wouldn't rely on this argument.

-Gene