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User name V. Sulkosky
Log entry time 10:48:40 on November 18, 2008
Entry number 249525
keyword=VDC T0's Versus Time (resubmission)My first attempt to submit this failed for some reason, though it did
email everyone.
With Chiranjib's help, we analyzed about two dozen runs to map out the
VDC T0 change versus time/run number. All these runs are from
production kinematics that we have taken with fifth pass beam. I have
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 November 17, runs: (3544-3611)
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.
Figure 1 is from the artistic talents of Chiranjib and shows the VDC T0
history for the three periods of time in question for each VDC plane.
Here is the brief summary:
1) In each period, the T0 appears reasonably stable to within a few ns.
2) Period I also contains the VDC gas problem that began around
run 3097. At run 3112, we lost beam for about 8 hours. During that
day shift the efficiency drop was walking across the U planes. I
assume this continued into the V planes while we were down. In either
case, the U planes were more sensitive than the V planes.
3) The only time the T0's showed any real drift was within the first
shift of production, then they hardened except for the when the gas
system shut down on the morning of November 9th. After the VDC
recovered the T0's were stable for the next two days.
4) All the main shifts occurred after we were down and had an access.
The shift between the first and second period was expected. It seems
that these shifts are correlated with us being down and in an access.
5) All indications point that the shift in the third period is a side
affect of something that was done to the timing which had unexpected
consequences.
A copy of this log entry has been emailed to: vasulk
VDC T0 Drift History
