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<p>Friends,</p>
<p>Please find the minutes below and at</p>
<p>
<a class="moz-txt-link-freetext" href="https://halldweb.jlab.org/wiki/index.php/GlueX_TOF_Meeting,_March_28,_2018#Minutes">https://halldweb.jlab.org/wiki/index.php/GlueX_TOF_Meeting,_March_28,_2018#Minutes</a>
.</p>
<p> -- Mark</p>
<p>_______________</p>
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<h2 id="firstHeading" class="firstHeading" lang="en"><span
dir="auto">GlueX TOF Meeting, March 28, 2018, </span><span
class="mw-headline" id="Minutes">Minutes</span></h2>
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<p>Present:
</p>
<ul>
<li> <b> FSU: </b> Sasha Ostrovidov</li>
<li> <b> JLab: </b> Thomas Britton, Eugene Chudakov,
Mark Ito (chair), Simon Taylor, Beni Zihlmann</li>
</ul>
<p>There is a <a rel="nofollow" class="external text"
href="https://bluejeans.com/s/zCEdu/">recording of
this meeting</a> on the BlueJeans site. Use your JLab
credentials.
</p>
<h3><span class="mw-headline"
id="Changing_the_Hit_Factory">Changing the Hit Factory</span></h3>
<p>Beni has changed the TOF hit reconstruction code to use
the FADC integral for the time-walk correction in the
case that the amplitude is set to zero. Recall that this
can happen when the voltage is above threshold at the
beginning of the FADC read-out window. The ratio used is
a hard-wired 0.2 (amplitude/integral). He analyzed a
file both before and after this change and sees an
increase in TOF efficiency. See <a rel="nofollow"
class="external text"
href="https://logbooks.jlab.org/entry/3547610">logbook
entry 3547610</a> for plots that demonstrate the
improvement. It can be greater than 10% in certain
regions of the detector.
</p>
<p>The timing resolution appears to be a bit worse with
the change, but a quantitative assessment is still in
progress. Part of this may come from an apparent shift
in the timing calibration constants. This is not
expected and not understood.
</p>
<h3><span class="mw-headline"
id="Review_of_minutes_from_the_March_14_meeting">Review
of minutes from the March 14 meeting</span></h3>
<p>We went over the <a
href="https://halldweb.jlab.org/wiki/index.php/GlueX_TOF_Meeting,_March_14,_2018#Minutes"
title="GlueX TOF Meeting, March 14, 2018">minutes</a>.
</p>
<h4><span class="mw-headline"
id="High_Rates_and_Missed_Pulses">High Rates and
Missed Pulses</span></h4>
<p>There was further discussion of the presentation Beni
made at the last meeting on losses at high rates.
</p>
<ul>
<li> There were "missing channels" where FADC read-out
was completely apparently absent from the event for
channels were a pulse was expected. This was a bug.
Those pulses are indeed there in the data.</li>
<li> The FADC read-out thresholds have been raised for
the TOF from 110 counts to 160. This should improve
efficiency. The level was chosen to be a bit below
that of the discriminatory threshold (thus on the TDC
side, note that the signal split is 50-50).</li>
<li> The feature of the firmware where "peak=0" is
reported is allegedly fundamental in the algorithm and
not easy to change.</li>
<li> We need to explore schemes where full waveform
read-out is done, either selectively, or for every
event, because of lost information at high rates.</li>
<li> Beni found out that there is an intrinsic dead-time
in the discriminator of 20 to 25 ns, independent of
input pulse width. This was chosen to match the
dead-time of the F1-TDC. Since we are using CAEN TDCs
in the TOF, this limits our double pulse separation
capability. As a result, a discriminator width of 20
ns is used universally in GlueX.</li>
</ul>
<h4><span class="mw-headline"
id="Amplifier-in-the-Base_Tests">Amplifier-in-the-Base
Tests</span></h4>
<p>We need to study how to deal with the significant
baseline shift incurred by the AC coupling of the
amplifier-in-the-base scheme.
</p>
<h3><span class="mw-headline" id="PMT_testing">PMT testing</span></h3>
<p>In order to look the apparently poor quantum efficiency
he was seeing for some PMTs with an LED light source,
Sasha set up a test with an Americium source. With this
set all PMTs give roughly similar and acceptable
efficiency. The cause of the problem with the LED set-up
is still under investigation.
</p>
<p>Beni asked about gains. The new tubes have gains in the
range of 4 to 6×10<sup>6</sup>.
</p>
<h3><span class="mw-headline" id="Action_Item_Recap">Action
Item Recap</span></h3>
<ul>
<li> Add items to the list of tests to perform with the
remaining run time during Spring 2018:
<ol>
<li> Test the effect of the raised FADC read-out
threshold.</li>
<li> Look with a scope at the discriminator input
for the amplifier-in-the-base channel.</li>
</ol>
</li>
<li> Initiate process of shipping tested PMTs back to
JLab from FSU.</li>
</ul>
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