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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,_April_2,_2020#Minutes">here</a>
and below.</p>
<p> -- Mark</p>
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<h2 id="firstHeading" class="firstHeading" lang="en"><span
dir="auto">GlueX Start Counter Meeting, April 2, 2020, </span><span
class="mw-headline" id="Minutes">Minutes</span></h2>
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lang="en">
<p>Present: Rupesh Dotel, Tolga Erbora, Mark Ito, Simon
Taylor, Beni Zihlmann
</p>
<p>There is <a rel="nofollow" class="external text"
href="https://bluejeans.com/s/5BYw8/">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_minutes_from_the_last_meeting">Review
minutes from the last meeting</span></h3>
<p>We went over <a
href="https://halldweb.jlab.org/wiki/index.php/GlueX_Start_Counter_Meeting,_March_5,_2020#Minutes"
title="GlueX Start Counter Meeting, March 5, 2020">the
minutes from March 5</a> without significant comment.
</p>
<h3><span class="mw-headline"
id="Calibration_and_Efficiency">Calibration and
Efficiency</span></h3>
<p>Rupesh showed counter-by-counter time resolution for
the start counter after the propagation-time
calibration. See <a
href="https://halldweb.jlab.org/wiki/images/f/f5/April2_2020_SC.pdf"
class="internal" title="April2 2020 SC.pdf">his slides</a>
for the plots. At Sean's suggestion he tried applying
constants obtained from run 71724 to data from run 71724
itself to see if there was a significant improvement
over resolution using constants obtained from run 71003.
Only slight improvement was visible.
</p>
<p>The constants from run 71724 have been entered into the
default CCDB variation for all of the
Fall-2019/Spring-2020 run. Rupesh is looking at
calibrating a few more runs dispersed throughout the run
and applying them appropriately to smaller time periods
of the run.
</p>
<h3><span class="mw-headline" id="Dark_Rate_Studies">Dark
Rate Studies</span></h3>
<p>Beni showed the results from dark rate runs. See the
plot below. The y-axis is the ratio of the area of a
Gaussian fitted to the pedestal distribution, but using
only the low side of the distribution, to the area of
the entire pedestal distribution, as he described in a <a
rel="nofollow" class="external text"
href="https://halldweb.jlab.org/doc-private/DocDB/ShowDocument?docid=4138">GlueX
Doc from last year</a>. The x-axis is accumulated
coincidences from the pair spectrometer as a proxy for
beam photon flux. Significant increase in dark current
is seen.
</p>
<div class="thumb tright">
<div class="thumbinner" style="width:600px;"><a
href="https://halldweb.jlab.org/wiki/index.php/File:Sc_dr_ped.gif"
class="image"><img alt=""
src="https://halldweb.jlab.org/wiki/images/f/f9/Sc_dr_ped.gif"
class="thumbimage" width="598" height="374"></a>
<div class="thumbcaption">Development of the Start
Counter SiPM Dark rate over the PrimEx and Fall 19
run period. This is based on the pedestal data
reported by the F250 firmware running in raw mode,
unsparsified with no beam, taken with a random
trigger.</div>
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<p>Tolga has started reviewing Beni's code and will try to
reproduce these results.
</p>
<h3><span class="mw-headline" id="Action_Item_Review">Action
Item Review</span></h3>
<ol>
<li> Obtained calibrations for sub-periods of the recent
run. (Rupesh)</li>
<li> Reproduce Beni's dark current results. (Tolga)</li>
</ol>
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