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<p>Folks,</p>
<p>Please find the minutes below and <a moz-do-not-send="true"
href="https://halldweb.jlab.org/wiki/index.php/GlueX_TOF_Meeting,_July_18,_2018#Minutes">here</a>.</p>
<p> -- Mark</p>
<p>_____________________</p>
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<h2 id="firstHeading" class="firstHeading" lang="en"><span
dir="auto">GlueX TOF Meeting Minutes, July 18, 2018</span></h2>
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lang="en">
<p>Present:
</p>
<ul>
<li> <b> FSU: </b> Sean Dobbs, Sasha Ostrovidov</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/mDCze/">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_June_6_meeting">Review
of minutes from the June 6 meeting</span></h3>
<p>We reviewed the <a
href="https://halldweb.jlab.org/wiki/index.php/GlueX_TOF_Meeting,_June_6,_2018#Minutes"
title="GlueX TOF Meeting, June 6, 2018">minutes</a>
without comment.
</p>
<h3><span class="mw-headline" id="Calibration_Status">Calibration
Status</span></h3>
<p>Beni reported that the constants for 2018 have been put
into the CCDB. There is a small difference from previous
constants in that a small shift in the TOF vs. RF time
seems have occurred. Sean thought that it might be due
to changes in the tracking code.
</p>
<h3><span class="mw-headline"
id="Study_of_amplified_base_performance">Study of
amplified base performance</span></h3>
<p>Beni reviewed <a rel="nofollow" class="external text"
href="https://halldweb.jlab.org/talks/2018/specialtof.pdf">his upcoming
GlueX note</a> looking at the time resolution we
obtained with the amplified base during the last run.
For all the details please see his note.
</p>
<p>The set-up has
</p>
<ul>
<li> a test paddle, with the left end having a standard
tube/base and the right end having the base with
built-in amplification.</li>
<li> paddle 21, of the existing front horizontal array,
directly behind and parallel to the test paddle</li>
<li> paddle 14, of the existing rear vertical array</li>
</ul>
<p>He used three methods to get at the time resolution.
</p>
<ol>
<li> Using coincidences between the test paddle and
paddle 14, measure the width of the end-to-end time
difference in the test paddle (given a hit in paddle
14) and the width of the time difference in paddle 14,
given a hit in the test paddle). Also do the same
exercise for paddle 21 and paddle 14.</li>
<li> Use coincidences between the test paddle and paddle
21. Since true coincidences are the same difference
from the left PMT of the test paddle and the left PMT
of paddle 21, the difference in time of these two
channels shows a peak. Likewise for the right PMTs of
the two paddles.</li>
<li> Using coincidences between the test paddle and
paddle 14, he looks at the time difference between,
say, the right PMT of the test paddle and the top PMT
of paddle 14. Since true coincidences come from the
small area of intersection between the two crossed
paddles, the time distribution shows a clear peak.
These distributions are obtained for the other
combinations as well, namely for right-test vs.
bottom-14, left-test vs. top-14 and left-test vs.
bottom 14. The same four distributions are obtains for
paddle 21 vs. paddle 14.</li>
</ol>
<p>The results from each of these, vis-a-vis the
resolution of the amplified base PMT are not completely
clear, though likely worse than a standard tube by a
significant factor (30%-100% depending on the method).
Sasha pointed out that since paddle 14 is significantly
closer to the amplified base PMT than the standard base
PMT, it has an advantage in since it should have more
photoelectrons on average. Beni is going to repeat the
study using vertical paddle 30, which is equidistant
from the beam line as paddle 14 on the opposite side.
</p>
<h3><span class="mw-headline" id="Geometry_.26_Alignment">Geometry
& Alignment</span></h3>
<p>Sean proposed a parametrization scheme for small
corrections to the TOF geometry. He showed a <a
rel="nofollow" class="external text"
href="https://halldweb.jlab.org/wiki/images/7/77/Sdobbs_TOF_June2018.pdf">diagram</a>
of the current geometry and the proposed upgraded
geometry to guide the discussion. The proposal is to
have three global translation corrections and one global
rotation (about z). Also to have two inter-counter
spacing parameters, one for the front array and one for
the back. Beni remarked that there is probably no need
for these corrections since the TOF is never used for
precise geometrical information, but we agreed that even
if the parameters exist, we are not forced to use them.
Sean is willing to do the coding to provide the
adjustment mechanism in any case.
</p>
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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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