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<p>PID'lers,</p>
<p>Please find the minutes below and at
<a class="moz-txt-link-freetext" href="https://halldweb.jlab.org/wiki/index.php/GlueX_Start_Counter_Meeting_September_21,_2017#Minutes">https://halldweb.jlab.org/wiki/index.php/GlueX_Start_Counter_Meeting_September_21,_2017#Minutes</a>
.</p>
<p> - Mark</p>
<p>_____________</p>
<p>
</p>
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<h2 id="firstHeading" class="firstHeading" lang="en"><span
dir="auto">GlueX Start Counter Meeting September 21, 2017,
</span><span class="mw-headline" id="Minutes">Minutes</span></h2>
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lang="en">
<p>Present:
</p>
<ul>
<li> <b> FIU </b>: Werner Boeglin, Mahmoud Kamel</li>
<li> <b> FSU </b>: Sean Dobbs</li>
<li> <b> JLab </b>: Thomas Britton, Mark Ito (chair),
Simon Taylor, Beni Zihlmann</li>
</ul>
<p>There is a <a rel="nofollow" class="external text"
href="https://bluejeans.com/s/FU0KH/%E2%80%8E">recording
of this meeting</a> on the <a rel="nofollow"
class="external text"
href="https://jlab.bluejeans.com/">BlueJeans site</a>.
Use your JLab credentials to authenticate.
</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,_August_24,_2017#Minutes"
title="GlueX Start Counter Meeting, August 24, 2017">minutes
from August 24</a>.
</p>
<ul>
<li> Thomas suspects that here may be a clocking problem
with the start counter in <b> HDvis </b> that needs
to be looked at. Mahmoud expressed interest in playing
with HDvis with an event source. Thomas will send him
email with instructions.</li>
<li> Werner recently sent some final plots to Eric
Pooser for the <b> NIM paper.</b> The FIU folks want
to get together one more time before general release,
but Werner thinks they are pretty close now.</li>
</ul>
<h3><span class="mw-headline"
id="Calibration_and_Efficiency">Calibration and
Efficiency</span></h3>
<p>Mahmoud brought us up-to-date on his efficiency
analysis. Please see <a rel="nofollow" class="external
text"
href="https://halldweb.jlab.org/talks/2017/Analysis_Meeting_9_20_2017.pdf">his
slides</a> for the plots and details.
</p>
<p>He has changed the procedure to use the RF signal as a
time reference for the start counter hits in his
efficiency calculation, cutting the resulting time
difference to decide whether a counter is hit or not. He
is correcting for the target z position of the event
vertex, the time-of-flight from the target to the start
counters, light propagation in the counters and
z-position of the hit in the counters. The time
difference has the expected prominent peak at zero, but
with not insignificant (few percent) nearest-neighbor RF
bucket peaks and smaller next-to-nearest-neighbor peaks
as well. Interpretation of these peaks as accidental
background gives a artificially low efficiency after
subtraction. There were several suggestions about things
to try.
</p>
<ul>
<li> Beni advised avoiding RF times that were chosen
based on the start counter.</li>
<li> Beni provided guidance on which RF factory product
should be used.</li>
<li> Mark suggested selecting events where the event
vertex is well defined, either those with multiple
tracks or those with tracks that go transverse to the
beamline. That may give events with better RF bucket
choices.</li>
<li> Mark mentioned calculating efficiency treating the
neighboring peaks as signal and getting the accidental
correction from RF peaks far away from zero where the
time distribution looks flat (just to see what you
get).</li>
</ul>
<h3><span class="mw-headline"
id="Separating_tracking_contribution_to_resolution_in_mcsmear">Separating
tracking contribution to resolution in mcsmear</span></h3>
<p>Sean led us through his <a
href="https://halldweb.jlab.org/wiki/index.php/SC_mcsmear_resolutions"
title="SC mcsmear resolutions">wiki page</a> where he
studies, in simulated data, the dependence of the
measured start counter timing resolution on the amount
of start counter time smearing input to mcsmear. Roughly
speaking, he measures something about 10% broader than
the smearing we put in. This is likely due to the
contribution to the resolution from tracking that is
intrinsic to the measurement.
</p>
<p>Sean uses an empirical linear function to capture this
effect, on a counter-by-counter basis. We all agreed
that this should be implemented into mcsmear at some
point. Sean also pointed out that there may be an even
bigger effect to include, that of the dependence of time
resolution on the z-position of the hit in the start
counter.
</p>
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