[Halld] Timing shifts last night

[Sean Dobbs]

Hi all,

It looks like the monitoring plots over last night were affected by a 2ns
shift of the RF time with respect to the rest of the detector.  This has
now been corrected, for more details see here:
https://logbooks.jlab.org/entry/3514776
Please take a look at this data and let me know if you see any more
problems.

We could probably use some extra online monitoring for this, and then if
the shift crew notices a shift (very clear due to the bifurcation in Delta
T_RF plots, since the shift is half the RF time), my best suggestion at the
moment is for the shift crew to contact an offline expert (I guess me at
the moment).  As seen, this really screws up the reconstruction, but it
happens rarely enough that I haven't figured out a method that is more than
50% effect (since the shifts could be +- 2 ns).

Cheers,
Sean
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