Left HRS VDC T0 Drifts

For the fifth pass production data, we can split the runs into three periods:

Period I:   November 8 to November 11,  runs: (3036-3203) 
Period II:  November 12 to November 13, runs: (3304-3323) 
Period III: November 16 to present,     runs: (3528-present) 

During Period I, the T3 delay at the BigBite Weldment was set to 60 ns.
There is a short period of time, when the delay was 76 ns (runs 3117-3124).
None of these runs are production.

For Period II, all the T3 delay was removed and the T1 delay was changed
to move the coincidence peak into the middle of the window.

Period III began after the 2.5 day down due to the CHL problem. As far as we
know, there were no timing changes between Period II and III, however, re-timing
was set up for the BigBite triggers.

See Halog entry for further details on this figure:

Study of VDC T0 Drift in HALOG

The First Period Up Close

The next figure shows Period I including runs at the beginning of this production
period and also all the runs when the gas system shut down on November 9, 2008. From
this analysis, the affected runs are 3106 through 3112. The U1 and U2 planes are defintely
more problematic than the V1 and V2 planes. Prior to the gas problem, there is clear evidence
that the T0's were drifting to smaller values by a few ns over a period of a day or so.

Starting with run 3125, after the VDC's had recovered, the time offsets appear to stabilize until
we stopped production on the morning of November 11th.