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Folks,<br>
<br>
Find the minutes below and at<br>
<br>
<a class="moz-txt-link-freetext" href="https://halldweb.jlab.org/wiki/index.php/GlueX_Start_Counter_Meeting,_April_28,_2015">https://halldweb.jlab.org/wiki/index.php/GlueX_Start_Counter_Meeting,_April_28,_2015</a><br>
<br>
-- Mark<br>
__________________________________________<br>
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<span dir="auto">GlueX Start Counter Meeting, April 28, 2015</span><br>
<div id="bodyContent" class="mw-body-content"><span
class="mw-headline" id="Minutes">Minutes</span><br>
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lang="en">
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Present:
<br>
<ul>
<li> <b>FIU</b>: Werner Boeglin, Mahmoud Kamel</li>
<li> <b>JLab</b>: Mark Ito (chair), Eric Pooser, Beni
Zihlmann</li>
</ul>
<br>
<span class="mw-headline" id="News_from_the_Run">News from
the Run</span><br>
<ul>
<li> With a 200 nA beam on a 3×10<sup>-4</sup> radiator,
Eric reported see rates from 100 to 200 kHz in the
individual start counter sectors.</li>
<li> When beam started up last Friday, the scalers rate
distribution was symmetric, but recent log entries
show an asymmetry of 10 to 20% in the rates. The cause
is not understood at present. It is nothing like the
asymmetry we saw last Fall when the start counter was
tilted by about 6 degrees. Werner remarked that we
should expect some level of asymmetry in the raw
scalers rates.</li>
<li> Werner asked about whether thresholds in the
discriminators can be set on a channel-by-channel
basis. Eric told us that the boards accept different
thresholds, but our current software can only load a
single value for all channels on a board.</li>
<li> Bias voltages on the SiPMs are currently all set as
per Hamamatsu's recommendation, as tabulated by Nick
and Fernando. Recall the four SiPMs for a given sector
are all run from a common voltage channel.</li>
</ul>
<br>
<span class="mw-headline" id="Bias_Voltage_Scan">Bias
Voltage Scan</span><br>
<br>
We discussed a plan to scan bias voltages for the SiPMs.
This has never been done for the start counters, including
during fabrication and testing at FIU. The study would
tell us if we should pursue gain balancing among the
sectors. Eric reminded us that the gain should change by
about one percent per 10 mV change in bias voltage. We
decided on a plan to vary the voltages in the range of
-200 mV to +200 mV from nominal over the next few days,
changing setting after we accumulate a significant chunk
of data (a few hours of beam). Thus the gain should only
change in the range of -20% to 20% during this exercise.
<br>
<br>
<span class="mw-headline" id="Calibration">Calibration</span><br>
<br>
Calibration work is still in progress, both the time-walk
correction and propagation delay correction scheme are
evolving. Eric also mentioned that there will be some work
to incorporate the new calibration schemes in the PID
library.
<br>
<br>
<span class="mw-headline" id="Next_Meeting">Next Meeting</span><br>
<br>
We agreed to go to a two-week schedule, starting after the
collaboration meeting.
<br>
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