[Halld-pid] Time-of-Flight Meeting Minutes, November 29, 2016

[Mark Ito]

Folks,

Please find the minutes below and at 
https://halldweb.jlab.org/wiki/index.php/GlueX_TOF_Meeting,_November_29,_2016#Minutes 
.

   -- Mark

__________________________


    GlueX TOF Meeting, November 29, 2016, Minutes

Present:

  * *FSU*: Sasha Ostrovidov
  * *JLab*: Thomas Britton, Brad Cannon, Eugene Chudakov, Mark Ito
    (chair), Simon Taylor, Beni Zihlmann


      Review of minutes from the previous meeting

We reviewed the [[GlueX TOF Meeting, November 15, 2016#Minutes|minutes 
of the November 15 meeting.

  * The four ADC channels that were dead actually had a problem with the
    DAC that sets the baseline. These channels seem to have a bit
    missing (or stuck) such that the baseline finding algorithm gets
    confused. The apparent lack of hits was due to a wildly mis-set
    baseline value. Beni figured this out and set the baseline values by
    hand.
  * Beni tried to reverse the INL correction of the Spring data but
    realized that the function that makes the correction is not
    invertible. He has abandoned that effort. He did notice that some of
    the channels have INL profiles quite different from what he has seen
    before.
  * Beni reports that the HV scan software is working with ROOT 6 now.
  * Sasha reports that he fixed the Lecroy 1440 mainframe at FSU. He
    will not need a replacement from JLab.
  * We will likely send the new PMTs to FSU for testing. The property
    and shipping procedure is not onerous.


      PMT bases with Amplifiers

  * Beni is collecting information to pass on to Vladimir Popov for his
    design.
  * We need to make a decision about whether to re-use the voltage
    divider chain on in the bases, introducing the possibility of a
    mezzanine board, or re-adjust the voltages to optimize for lower HV
    operation. Beni will think about doing a test with the laser to
    measure the degradation in time resolution with lower voltage.


      Efficiency Study

Beni went through his wiki page 
<https://halldweb.jlab.org/wiki/index.php/TOF_Efficiencies> describing a 
study of TOF efficiency using charged particles. See his page for 
details and plots.

  * Beni concludes that using tracking to measure efficiency is tricky.
  * The effect if high rates is two-fold: it causes more accidentals,
    artificially increasing efficiency, and can reduce the gain of tube,
    causing a real loss of efficiency due to low pulse amplitude.
  * There is a marked dependence of the method on the momentum of the
    charged tracks. At 3 GeV/c, efficiency is measured to be acceptably
    high in the bulk of the TOF.
  * At the extreme edges of the array there is a marked reduction of
    efficiency. Simon thought that this is likely due to tracks which
    are projected to the TOF but actually encounter the BCAL on the way.
    Beni will investigate.


      TOF Time Resolution for Charged Tracks

Brad presented slides describing his study 
<https://halldweb.jlab.org/talks/2016/TOF%20PMT%20Study.pdf>. He looked 
at the resolution of the difference between the corrected TOF time 
(corrected for charged track propagation time) and the RF time. He sees 
significant degradation of resolution as the number of TOF hits used to 
construct a TOF point is reduced. See his slides for details.


      Cosmics test at FSU

Sasha went through his wiki page 
<http://hadron.physics.fsu.edu/%7Eostrov/tof/20161129/> describing a 
recent timing measurement he did with his test set-up using 1200 V and 
1500 V on the PMTs. The at 1500 V he sees 161 ps and that degrades to 
187 ps at 1200 V, a 16% increase. No walk corrections were applied; 
these may have a significant effect on the comparison. He also showed a 
similar, though not identical, measurement from 2009 that gave 124 ps 
for the same quantity. He plans to repeats this measurement using a 
constant-fraction discriminator.

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