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<pre wrap="">Dear Colleagues,
The minutes for last weeks Friday meeting are given below and can
also be found at:
<a class="moz-txt-link-freetext" href="http://www.jlab.org/primex/wiki/index.php/Weekly_Minutes_2009-11-13">http://www.jlab.org/primex/wiki/index.php/Weekly_Minutes_2009-11-13</a>
Best regards,
Dustin
Dustin McNulty
TJNAF CEBAF Center, Rm A102
12000 Jefferson Avenue
Newport News, VA 23606
Phone: (757) 269-5023
</pre>
<p align="left"><br>
<font size="6"><b>Weekly Meeting Minutes - November 13, 2009</b></font></p>
<p>Minutes by: Dustin McNulty</p>
<a
href="http://www.jlab.org/primex/wiki/index.php/PrimEx_Weekly_Meeting%2C_November_13%2C_2009">Meeting
Agenda</a>
<hr>
<p><b>Attending:</b> P. Ambrozewicz, M. Ito, D. Lawrence, D. McNulty,
V. Tarasov, A. Teymurazyan
<b>By phone:</b> R. Miskimen</p>
<p><b>
<h1>Summary of Meeting Discussions:</h1>
</b></p>
<p></p>
<h3><b>All.</b> Nominate secretary: (next secretary: Mark) </h3>
<h3><b>All.</b> Approval of last meeting's minutes: </h3>
Approved. You can find the previous meeting minutes <a
href="http://www.jlab.org/primex/wiki/index.php/Weekly_Minutes_2009-10-30">here</a>.
Only comments were about Aram's presentation of hadronic bkgd studies;
he showed a 1 to 1 signal to bkgd ratio for eta production integrated
over the full production angle range. Question for him was: What are
the reactions giving rise to the hadronic bkgd eta's? All we know is
that they are not from gamma+p-->eta+p.
<p></p>
<h3><b>All.</b> New Business: Itemized below</h3>
<u>1</u>: <a
href="http://www.jlab.org/primex/weekly_meetings/slides_2009_11/Study%20of%20properties%20beam%20line%20in%20Pair%20spectrometer_5.pdf">Review
of collimator size studies (Victor)</a>:
<ul>
He looked at the effect of 2 different collimator sizes: 3.4mm and
5.0mm diameter (this is for the active collimator)
</ul>
<ul>
The purpose of the study was to examine how the coll. size affects the
energy resolution of the pair spectrometer.
</ul>
<ul>
For the 3.4mm case, 1.49M gammas emerged from the collimator out of 10M
gammas incident.
</ul>
<ul>
For the 5.0mm case, 1.52M gammas emerged from the collimator out of 10M
gammas incident.
</ul>
<ul>
Victor showed plot of electron-arm's (from pair prod) Esigma
versus distance detected from beamline (at the pair spec detector
location). He determined Esigma by (Gaussian) fitting the distribution
of electron energies seen in a 10cm wide x bin.
</ul>
<ul>
His results seemed to indicate a general trend of worsening
resolution for greater distances from the beamline, although it was
noted that the statistical precision was quite low and that he should
include error bars on his points to see if some of the observed
fluctuations were real or not. Also, he should generate more stats.
</ul>
<ul>
Dustin commented that the 10cm bin size seemed an artificial
choice and that he should, if possible, use the actual bin size
proposed for the physical counters--since the results will likely
depend on this.
</ul>
<ul>
Dustin also noted that Victor should quote the photon beam
characteristics used in his Monte Carlo (spot size at radiator,
emittance properties, etc) since these may also impact the outcome.
</ul>
<u>2</u>: <a
href="http://www.jlab.org/primex/weekly_meetings/slides_2009_11/bggen-plots.pdf">Presentation
of hadronic bkgd studies for eta Primakoff experiment (Pawel)</a>:
<ul>
Pawel used BGgen with events generated between 6 and 12 GeV on 30cm
proton target (using Pythia).
</ul>
<ul>
Showed plot of number of clusters in FCal versus No. of clusters
per event (with no cuts). Aram noted that, for no cuts, the zero
cluster bin look surprisingly low.
</ul>
<ul>
Showed two cluster invariant mass distribution. This looked like
there was much less background in the vicinity of the eta mass (as
compared with Aram's study). It was also noted that the eta inv mass
hump was shifted by +50MeV. David thought this could have something to
do with how the reaction vertex was incorporated in the calculation.
</ul>
<ul>
Showed two cluster elasticity plot for all possible pair combinations.
</ul>
<ul>
Showed eta angular distribution using a 9GeV elasticity cut and
cutting around the eta inv mass hump. It was noted that these events
include the g+p->eta+p reaction.?
</ul>
<ul>
Conclusions are that more statistics are needed, but that in
general the background looks very low (compared with Aram). Aram
suggests that Pawel should generate events with energy closer to the
actual trigger conditions of the proposed experiment (which is
E>10.5GeV)--this will improve the efficiency of the Monte Carlo.
</ul>
<u>3</u>: <a
href="http://www.jlab.org/primex/weekly_meetings/slides_2009_11/A.Teymurazyan_bg_11_06_2009.pdf">Presentation
of hadronic bkgd studies for eta Primakoff experiment (Aram)</a>:
<ul>
BGgen of hadronic events using Pythia with the g+p->eta+p
reaction explicitly excluded. Aram analyzed 46M events between 10.2 and
11.7 GeV with only incoherent Bremsstrahlung on 30cm liquid proton
target, the solenoid was energized, and the full setup of the GlueX
detector simulation was employed.
</ul>
<ul>
Showed cluster distributions in FCal. In general his left-side
plots had limited or no cuts while the right-side plots had cuts. His
cuts were total energy in FCal (all cluster energies summed) > 9GeV,
2 or more clusters detected, 2 cluster elasticity between 0.9 and 1.1,
and inv mass between 490 and 650MeV.
</ul>
<ul>
His results for the background eta were the same as he presented
two weeks ago--Over the full production angle range, there is a 1 to 1
ratio of signal to noise (S2N). He also examined the S2N in the
Primakoff peak region (for 1 to 0.5 deg) and found that here the S@N
ratio is 1:8.
</ul>
<ul>
Aram noted that this work is very preliminary and needs to be checked
with more investigation.
</ul>
<ul>
A discussion started about the accuracy of Pythia, it was noted
that this program was brought by Elke from HERMES (where it was used
for 30GeV event generation) and modified/tuned to work for Hall D
energies and that it may not be very accurate in the 0 to 0.5 degree
region. However, it was also noted that it is just as likely to be
underestimating the background here as it is to be overestimating it.
</ul>
<ul>
It was suggested by Rory and Dustin that Aram try to eliminate the
inelastic bkgd events within his elasticity cut to give more accurate
results -- it looks like this smooth inelastic bkgd could be
significant. Also, the smooth background under the eta inv mass peak
could be eliminated in the same way (this bkgd looked even more
significant).
</ul>
<ul>
Aram will check his numbers for the S2N and perhaps present them in a
more audience friendly format per Mark's request.
</ul>
<ul>
Aram also said that he will classify the events in his study in terms
of the reaction mechanism.
</ul>
<ul>
Another suggestion was for Aram to put the signal and background
distributions on the same plot.
</ul>
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