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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,_July_2,_2015#Minutes">https://halldweb.jlab.org/wiki/index.php/GlueX_Start_Counter_Meeting,_July_2,_2015#Minutes</a><br>
<br>
-- Mark<br>
_________________________________________<br>
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<span dir="auto">GlueX Start Counter Meeting, July 2, 2015</span><span
class="mw-headline" id="Minutes">, Minutes</span><br>
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<br>
Present:
<br>
<ul>
<li> <b>FIU</b>: Werner Boeglin</li>
<li> <b>JLab</b>: Mahmoud Kamel, Mark Ito (chair), Eric
Pooser, Simon Taylor, Beni Zihlmann</li>
</ul>
<br>
<span class="mw-headline" id="Calibrations">Calibrations</span><br>
<ul>
<li> There are two methods for measuring the light
propagation delay:
<ol>
<li> Take events with two hits in different start
counters and measure their time difference and
compare it to the difference in light propagation
distance. Eric has a new fitting procedure: first
cut the data into slices in z, fit each of those
and use the results to fit as a function of z. He
gets 11 cm/ns in the straight section, 16 cm/ns at
the bend, and 20 cm/ns in the nose. On the bench
at FIU he measured 19 cm/ns in the nose (method 2,
below).</li>
<li> At FIU delays were measured as a function of
position along the counters at fixed locations.
Eric has redone the fitting procedure, using a
method similar to that of method 1, automating
several steps which were done by hand before.</li>
</ol>
</li>
<li> To compare the two methods calibration constants
were generated for both. These have been put into a
private CCDB and the PID library was modified to
access the constants. Right now there is a problem
with the beam-data-generated constants. Eric is
looking into this now.</li>
<li> When Eric looks at start counter time corrected for
light propagation (using Simon's 15 cm/ns), for
particle time-of-flight, and for time of interaction
in target he gets widths of around 300 ps over most of
the start counter, consistent with our design goal.</li>
<li> We discussed a scheme where we simply measure time
delay as a function of position directly to get a
correction function or correction table to be
interpolated and applied, without explicit reference
to nose, bend, or straight. Although this is different
way of parametrizing the correction, Eric pointed out
that the framework for analyzing the data is the same
and is already developed.</li>
<li> From the FIU measurements there were measurable
differences in the propagation between paddles. At
present we do not have enough statistics to do a
paddle-by-paddle calibration using beam data.</li>
<li> Time-walk corrections have been revisited using the
fitting procedure he described for the propagation
delay. The parameters he gets are stable and uniform
counter-to-counter. The constants are in CCDB now.</li>
<li> Attenuation length measurement suffers from low
statistics, not enough even to do an
all-counters-together measurement. For now we will use
data from the bench data measured at FIU.</li>
</ul>
<br>
<span class="mw-headline" id="Plots_to_Show_at_Reviews">Plots
to Show at Reviews</span><br>
<br>
We discussed some possibilities for plots illustrative of
the status of the calibration. We settled on a
representative histogram of start counter time vs. RF
time, corrected for time-of-flight, light propagation in
scintillator, and the position of the interaction in the
target. Also a plot showing the resolution, obtained from
the aforementioned histogram, as a function of position in
the start counter.
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