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<p>Folks,</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_14,_2018#Minutes">https://halldweb.jlab.org/wiki/index.php/GlueX_TOF_Meeting,_March_14,_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 14, 2018, </span><span
class="mw-headline" id="Minutes">Minutes</span></h2>
<div id="bodyContent" class="mw-body-content">
<div id="mw-content-text" dir="ltr" class="mw-content-ltr"
lang="en">
<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/5iWhS/">recording of
this meeting</a> on the BlueJeans site. Use your JLab
credentials.
</p>
<h3><span class="mw-headline"
id="Review_of_minutes_from_the_January_31_meeting">Review
of minutes from the January 31 meeting</span></h3>
<p>We went over the <a
href="https://halldweb.jlab.org/wiki/index.php/GlueX_TOF_Meeting,_January_31,_2018#Minutes"
title="GlueX TOF Meeting, January 31, 2018">minutes</a>
without significant comment.
</p>
<h3><span class="mw-headline" id="Calibration_Status">Calibration
Status</span></h3>
<p>As reported last time, Beni has done a preliminary
calibration of 2018 data using early runs and has found
timing constants very close to those obtained in Sprint
2017. A complete calibration of all of the Spring 2018
data will have to to done at some point, but is not the
highest priority now (the run is officially still in
progress).
</p>
<h3><span class="mw-headline"
id="Amplified_Base_Prototype">Amplified Base Prototype</span></h3>
<p>Beni has been studying data take this year with the
amplifier-on-board PMT base mounted on a spare TOF
counter in the Hall.
</p>
<h4><span class="mw-headline" id="Resolution">Resolution</span></h4>
<p>He sees that the resolution of the test paddle (one end
with the amplifier-on-board the other end standard) is
about 20% worse than reference paddle 21 from the TOF
proper. This is one of the counters with the highest
rate.
</p>
<h4><span class="mw-headline" id="Going_Back_to_Basics">Going
Back to Basics</span></h4>
<p>He showed several <a rel="nofollow" class="external
text"
href="https://logbooks.jlab.org/files/2018/03/3544404/outputfile.pdf">plots
of recent raw waveform data</a> from <a
rel="nofollow" class="external text"
href="https://logbooks.jlab.org/entry/3544404">Logbook
Entry 3544404</a>. Each page potentially shows four
waveforms: the two ends of the test paddle and the two
ends of the reference paddle. A missing waveform
indicates that there was no waveform data for that end.
</p>
<p>His conclusions (exclamations marks his):
</p>
<ol>
<li> Algorithm is not adequate (due to high rates)!</li>
<li> Pulse_Peak zero as error flag causes TOF walk
correction to fail!</li>
</ol>
<p>From the discussion:
</p>
<ul>
<li> The pulses from the amplifier-on-board channel show
a significant baseline shift of about 20 ADC counts.</li>
<li> The results of the firmware summary data is also
read-out along with the waveform data making
comparison possible.</li>
<li> If the first few samples in the window are above
baseline, the the algorithm gets confused, often
reporting a leading edge at sample 1.</li>
<li> Also, in this case the peak amplitude is reported
as 0 (peak=0). Since the current walk algorithm works
on the peak amplitude, the hit, including TDC
information, is discarded (no walk correction
possible). This alone may account for the low
efficiency of the TOF in the high rate counters, an
effect that Beni identified months ago.</li>
<li> The algorithm is capable of identifying two or more
pulses in the raw read-out window, though some of the
results disagree what you can see by eye.</li>
<li> The minimum time difference for double pulse
separation by the algorithm is much less than that you
can see by eye, including cases where the first pulse
returns nearly to baseline.</li>
</ul>
<p>Bottom line is a large efficiency hit (30-50%) for high
rate counters at nominal photon flux due to the way the
firmware treats the raw data. In the limit of zero rate,
it seems to do fine, so the TOF rates are exposing the
problem.
</p>
<p>Amelioration strategies:
</p>
<ul>
<li> Fall back to using the integral for the time-walk
correction in cases where the amplitude is reported as
0.</li>
<li> Read out the waveform data and analyze timing and
amplitude offline for regular data taking:
<ol>
<li> with channel no sparsification (all channels
every event)</li>
<li> with channel sparsification (all channels above
threshold)</li>
<li> for selected channels, event-by-event (channels
which look problematic for the algorithm e. g.
peak=0)</li>
</ol>
</li>
<li> Change to firmware to not use amplitude=0 as a flag
for pedestal sensing problems.</li>
<li> More sophisticated peak finding algorithm in the
firmware.</li>
</ul>
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-- </div>
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<pre class="moz-signature" cols="72">Mark Ito, <a class="moz-txt-link-abbreviated" href="mailto:marki@jlab.org">marki@jlab.org</a>, (757)269-5295
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