[Halld-pid] Time-of-Flight Meeting Mintutes, July 18, 2018

[Mark Ito]

Folks,

Please find the minutes below and here 
<https://halldweb.jlab.org/wiki/index.php/GlueX_TOF_Meeting,_July_18,_2018#Minutes>.

   -- Mark

_____________________


    GlueX TOF Meeting Minutes, July 18, 2018

Present:

  * *FSU: * Sean Dobbs, Sasha Ostrovidov
  * *JLab: * Thomas Britton, Mark Ito (chair), Simon Taylor, Beni Zihlmann

There is a recording of this meeting <https://bluejeans.com/s/mDCze/> on 
the BlueJeans site. Use your JLab credentials.


      Review of minutes from the June 6 meeting

We reviewed the minutes 
<https://halldweb.jlab.org/wiki/index.php/GlueX_TOF_Meeting,_June_6,_2018#Minutes> 
without comment.


      Calibration Status

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 
<https://halldweb.jlab.org/talks/2018/specialtof.pdf> 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.

 1. 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.
 2. 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.
 3. 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 
<https://halldweb.jlab.org/wiki/images/7/77/Sdobbs_TOF_June2018.pdf> 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.

Retrieved from 
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  * This page was last modified on 18 July 2018, at 14:28.

-- 
Mark Ito, marki at jlab.org, (757)269-5295

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