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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Hello Beni, Mark,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">The SiPMs are replaceable individually or as PCB units of 12 SiPMs (3 channels). If radiation damage is suspected on any single SiPM on a PCB, I recommend replacing
the PCB unit as the other SiPMs might be approaching their limits as well. It is also possible to anneal the SiPMs at elevated temperatures for a period of time (no bias applied) by placing the PCB unit in a temperature controlled oven.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">I believe we have a couple of spare PCBs with all 12 SiPMs installed and ready for installation. Also, fabricating and assembling new PCBs is not a problem (I
think we may have a few spare bare PCBs). The cost is dominated by the SiPMs at about $50 each; a PCB unit will cost less than $1k if we need to procure PCBs and SiPMs in limited quantities.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Best regards,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Fernando<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">From:</span></b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> Halld-pid <halld-pid-bounces@jlab.org>
<b>On Behalf Of </b>Mark Ito<br>
<b>Sent:</b> Thursday, June 25, 2020 11:52 AM<br>
<b>To:</b> halld-pid@jlab.org<br>
<b>Subject:</b> [Halld-pid] Start Counter Meeting Minutes, June 25, 2020<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p>Folks,<o:p></o:p></p>
<p>Please find the minutes <a href="https://halldweb.jlab.org/wiki/index.php/GlueX_Start_Counter_Meeting,_June_25,_2020#Minutes">
here</a> and below.<o:p></o:p></p>
<p> -- Mark<o:p></o:p></p>
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<h2><span lang="EN">GlueX Start Counter Meeting, June 25, 2020, <span class="mw-headline">
Minutes</span><o:p></o:p></span></h2>
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<p><span lang="EN">Present: Eugene Chudakov, Rupesh Dotel, Tolga Erbora, Mark Ito (chair), Simon Taylor, Beni Zihlmann
<o:p></o:p></span></p>
<p><span lang="EN">There is <a href="https://bluejeans.com/s/FNL0_/">a recording of this meeting</a> on the BlueJeans site. Use your JLab credentials to gain access.
<o:p></o:p></span></p>
<h3><span class="mw-headline"><span lang="EN">Review of minutes from the last meeting</span></span><span lang="EN"><o:p></o:p></span></h3>
<p><span lang="EN">We went over the <a href="https://halldweb.jlab.org/wiki/index.php/GlueX_Start_Counter_Meeting,_May_28,_2020#Minutes" title="GlueX Start Counter Meeting, May 28, 2020">
minutes from May 28</a>. <o:p></o:p></span></p>
<h4><span class="mw-headline"><span lang="EN">Time Resolution Studies</span></span><span lang="EN"><o:p></o:p></span></h4>
<p><span lang="EN">Rupesh showed plots of time resolution for all thirty counters for a run late in the last run period, run 71840. Find his plots
<a href="https://halldweb.jlab.org/wiki/images/1/19/SCmeeting_June25.pdf" title="SCmeeting June25.pdf">
here</a> (starting with slide 3). Recall that last time he showed evidence for worsening of the resolution as a function of time as the run progressed when using calibration constants obtained early in the run. This time constants were obtained for run 71840
and applied to the same run. For this run, results were not much different than those with the earlier-in-the-run constants. He also tried a run even later in the run, 71???, which slowed slightly better resolution. To see if there was anything special about
run 71840, he looked other runs in the same run-number neighborhood. Those were all roughly the same as for 71840.
<o:p></o:p></span></p>
<p><span lang="EN">Eugene asked about the source of the counter-to-counter variation in resolution, noting that the pattern repeats for all runs shown. Beni and Simon attribute that to the rate variation from counter-to-counter due to a slight tilt of the assembly
and the concentration of the rate at the nose of the counters where small variations in distance from the beam make a big difference in rate.
<o:p></o:p></span></p>
<h4><span class="mw-headline"><span lang="EN">Gain Calibration</span></span><span lang="EN"><o:p></o:p></span></h4>
<p><span lang="EN">After the last meeting Sean Dobbs reported via email that an initial SC gain calibration was done by Simon back in 2015, and that has been what we are using so far. Beni also pointed out that the Start Counter NIM paper had dE/dx plots both
before and after "corrections." Rupesh and Beni will look at some recent monitoring plots to see if they give an indication about the current adequacy of the calibration.
<o:p></o:p></span></p>
<h4><span class="mw-headline"><span lang="EN">Improving Speed of Performing Calibrations</span></span><span lang="EN"><o:p></o:p></span></h4>
<p><span lang="EN">Rupesh consulted Beni after the last meeting and found that he could reduce the number of files analyzed for a calibration pass from the full run (over 200 raw data files) to 25 and still get reliable results. That turns a month into a few
days. <o:p></o:p></span></p>
<h3><span class="mw-headline"><span lang="EN">SiPM Replacement?</span></span><span lang="EN"><o:p></o:p></span></h3>
<p><span lang="EN">Beni raised the issue of how we might approach replacement of the SiPMs if we conclude, either now or in the future, that radiation damage is too severe to continue to use the current units. We need to talk to Fernando about whether it would
be easier to replace the SiPM on the current boards or just make new boards with new SiPMs. We would have to research the availability of the current units. Also, we would need a plan to do the replacement mechanically including locating any necessary support
jigs or structures. <o:p></o:p></span></p>
<h3><span class="mw-headline"><span lang="EN">Preparations for the Upcoming Run</span></span><span lang="EN"><o:p></o:p></span></h3>
<p><span lang="EN">Beni proposes that we leave the start counter alone until after the Fourth of July. After turn-on, he wants to take dark-current measurements (non-sparsified raw mode data) before beam arrives in the Hall. He recalled for us that that attempt
before the previous run was mis-configured, DAQ-wise, and the resulting data unusable.
<o:p></o:p></span></p>
<h3><span class="mw-headline"><span lang="EN">Action Item Review</span></span><span lang="EN"><o:p></o:p></span></h3>
<ol start="1" type="1">
<li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l0 level1 lfo1">
<span lang="EN">Document calibration procedure (Rupesh)<o:p></o:p></span></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l0 level1 lfo1">
<span lang="EN">Reproduce Beni's dark current results. (Tolga)<o:p></o:p></span></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l0 level1 lfo1">
<span lang="EN">Check status of the gain calibrations using monitoring histograms. (Rupesh, Beni)<o:p></o:p></span></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l0 level1 lfo1">
<span lang="EN">Revisit Yi's study of SiPM annealing. (Mark, Beni)<o:p></o:p></span></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l0 level1 lfo1">
<span lang="EN">Ask about the current recommendation from SciComp on copying files to the local disk from cache before analyzing them. (Mark)<o:p></o:p></span></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l0 level1 lfo1">
<span lang="EN">Ask Fernando about strategy for SiPM replacement (Mark, Beni)<o:p></o:p></span></li></ol>
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