GlueX TOF Meeting, July 18, 2018
GlueX Time-of-Flight Meeting
Wednesday, July 18, 2018
10:00 am EDT
JLab: CEBAF Center, Room F226
BlueJeans Meeting number is 350 531 998
- Review of minutes from the June 6 meeting
- Calibration Status
- Study of amplified base (Beni)
- Geometry & Alignment (Sean)
- Upgrade Plan
- NIM Paper (Paul)
- Action Item Recap
Talks can be deposited in the directory
/group/halld/www/halldweb/html/talks/2018 on the JLab CUE. This directory is accessible from the web at https://halldweb.jlab.org/talks/2018/ .
- FSU: Sean Dobbs, Sasha Ostrovidov
- JLab: Thomas Britton, Mark Ito (chair), Simon Taylor, Beni Zihlmann
There is a recording of this meeting on the BlueJeans site. Use your JLab credentials.
Review of minutes from the June 6 meeting
We reviewed the minutes without comment.
Beni reported that the constants for 2018 have been put into the CCDB. There is a small difference from previous constants in that a small shift in the TOF vs. RF time seems have occurred. Sean thought that it might be due to changes in the tracking code.
Study of amplified base performance
Beni reviewed his upcoming GlueX note looking at the time resolution we obtained with the amplified base during the last run. For all the details please see his note.
The set-up has
- a test paddle, with the left end having a standard tube/base and the right end having the base with built-in amplification.
- paddle 21, of the existing front horizontal array, directly behind and parallel to the test paddle
- paddle 14, of the existing rear vertical array
He used three methods to get at the time resolution.
- Using coincidences between the test paddle and paddle 14, measure the width of the end-to-end time difference in the test paddle (given a hit in paddle 14) and the width of the time difference in paddle 14, given a hit in the test paddle). Also do the same exercise for paddle 21 and paddle 14.
- Use coincidences between the test paddle and paddle 21. Since true coincidences are the same difference from the left PMT of the test paddle and the left PMT of paddle 21, the difference in time of these two channels shows a peak. Likewise for the right PMTs of the two paddles.
- Using coincidences between the test paddle and paddle 14, he looks at the time difference between, say, the right PMT of the test paddle and the top PMT of paddle 14. Since true coincidences come from the small area of intersection between the two crossed paddles, the time distribution shows a clear peak. These distributions are obtained for the other combinations as well, namely for right-test vs. bottom-14, left-test vs. top-14 and left-test vs. bottom 14. The same four distributions are obtains for paddle 21 vs. paddle 14.
The results from each of these, vis-a-vis the resolution of the amplified base PMT are not completely clear, though likely worse than a standard tube by a significant factor (30%-100% depending on the method). Sasha pointed out that since paddle 14 is significantly closer to the amplified base PMT than the standard base PMT, it has an advantage in since it should have more photoelectrons on average. Beni is going to repeat the study using vertical paddle 30, which is equidistant from the beam line as paddle 14 on the opposite side.
Geometry & Alignment
Sean proposed a parametrization scheme for small corrections to the TOF geometry. He showed a diagram of the current geometry and the proposed upgraded geometry to guide the discussion. The proposal is to have three global translation corrections and one global rotation (about z). Also to have two inter-counter spacing parameters, one for the front array and one for the back. Beni remarked that there is probably no need for these corrections since the TOF is never used for precise geometrical information, but we agreed that even if the parameters exist, we are not forced to use them. Sean is willing to do the coding to provide the adjustment mechanism in any case.