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<p>Folks,</p>
<p>Please find the minutes <a moz-do-not-send="true"
href="https://halldweb.jlab.org/wiki/index.php/GlueX_Start_Counter_Meeting,_June_25,_2020#Minutes">here</a>
and below.</p>
<p> -- Mark</p>
<p>
</p>
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<h2 id="firstHeading" class="firstHeading" lang="en"><span
dir="auto">GlueX Start Counter Meeting, June 25, 2020, </span><span
class="mw-headline" id="Minutes">Minutes</span></h2>
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lang="en">
<p>Present: Eugene Chudakov, Rupesh Dotel, Tolga Erbora,
Mark Ito (chair), Simon Taylor, Beni Zihlmann
</p>
<p>There is <a rel="nofollow" class="external text"
href="https://bluejeans.com/s/FNL0_/">a recording of
this meeting</a> on the BlueJeans site. Use your JLab
credentials to gain access.
</p>
<h3><span class="mw-headline"
id="Review_of_minutes_from_the_last_meeting">Review of
minutes from the last meeting</span></h3>
<p>We went over the <a
href="https://halldweb.jlab.org/wiki/index.php/GlueX_Start_Counter_Meeting,_May_28,_2020#Minutes"
title="GlueX Start Counter Meeting, May 28, 2020">minutes
from May 28</a>.
</p>
<h4><span class="mw-headline" id="Time_Resolution_Studies">Time
Resolution Studies</span></h4>
<p>Rupesh showed plots of time resolution for all thirty
counters for a run late in the last run period, run
71840. Find his plots <a
href="https://halldweb.jlab.org/wiki/images/1/19/SCmeeting_June25.pdf"
class="internal" title="SCmeeting June25.pdf">here</a>
(starting with slide 3). Recall that last time he showed
evidence for worsening of the resolution as a function
of time as the run progressed when using calibration
constants obtained early in the run. This time constants
were obtained for run 71840 and applied to the same run.
For this run, results were not much different than those
with the earlier-in-the-run constants. He also tried a
run even later in the run, 71???, which slowed slightly
better resolution. To see if there was anything special
about run 71840, he looked other runs in the same
run-number neighborhood. Those were all roughly the same
as for 71840.
</p>
<p>Eugene asked about the source of the counter-to-counter
variation in resolution, noting that the pattern repeats
for all runs shown. Beni and Simon attribute that to the
rate variation from counter-to-counter due to a slight
tilt of the assembly and the concentration of the rate
at the nose of the counters where small variations in
distance from the beam make a big difference in rate.
</p>
<h4><span class="mw-headline" id="Gain_Calibration">Gain
Calibration</span></h4>
<p>After the last meeting Sean Dobbs reported via email
that an initial SC gain calibration was done by Simon
back in 2015, and that has been what we are using so
far. Beni also pointed out that the Start Counter NIM
paper had dE/dx plots both before and after
"corrections." Rupesh and Beni will look at some recent
monitoring plots to see if they give an indication about
the current adequacy of the calibration.
</p>
<h4><span class="mw-headline"
id="Improving_Speed_of_Performing_Calibrations">Improving
Speed of Performing Calibrations</span></h4>
<p>Rupesh consulted Beni after the last meeting and found
that he could reduce the number of files analyzed for a
calibration pass from the full run (over 200 raw data
files) to 25 and still get reliable results. That turns
a month into a few days.
</p>
<h3><span class="mw-headline" id="SiPM_Replacement.3F">SiPM
Replacement?</span></h3>
<p>Beni raised the issue of how we might approach
replacement of the SiPMs if we conclude, either now or
in the future, that radiation damage is too severe to
continue to use the current units. We need to talk to
Fernando about whether it would be easier to replace the
SiPM on the current boards or just make new boards with
new SiPMs. We would have to research the availability of
the current units. Also, we would need a plan to do the
replacement mechanically including locating any
necessary support jigs or structures.
</p>
<h3><span class="mw-headline"
id="Preparations_for_the_Upcoming_Run">Preparations
for the Upcoming Run</span></h3>
<p>Beni proposes that we leave the start counter alone
until after the Fourth of July. After turn-on, he wants
to take dark-current measurements (non-sparsified raw
mode data) before beam arrives in the Hall. He recalled
for us that that attempt before the previous run was
mis-configured, DAQ-wise, and the resulting data
unusable.
</p>
<h3><span class="mw-headline" id="Action_Item_Review">Action
Item Review</span></h3>
<ol>
<li> Document calibration procedure (Rupesh)</li>
<li> Reproduce Beni's dark current results. (Tolga)</li>
<li> Check status of the gain calibrations using
monitoring histograms. (Rupesh, Beni)</li>
<li> Revisit Yi's study of SiPM annealing. (Mark, Beni)</li>
<li> Ask about the current recommendation from SciComp
on copying files to the local disk from cache before
analyzing them. (Mark)</li>
<li> Ask Fernando about strategy for SiPM replacement
(Mark, Beni)</li>
</ol>
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