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Greetings,<br>
<br>
From what I see there are 2 things,<br>
<br>
1) cos\theta 0.9 is very forward, I do not even think we have good
events past cos\theta 0.8. Especially with a 3 prong trigger.<br>
<br>
2) The mapping I created does pull most distributions high in the
cos\theta > 0.67, but as I said to Zulkaida and g12 members, this
is a known effect. I do not think g11 nor g1c was actually all that
accurate in the forward direction. You, Volker, are the person who
put me onto the fact that CLAS might have a forward acceptance
issue, since your analysis of the gp->ppi0 with TAPS showed a
higher XSection in the forward direction, which also matched that of
GRAAL and LEPS. <br>
When I compare gp->ppi0 with g1c, yes g12 is higher in the
forward direction, but so is the rest of the world. Therefore unless
there are other measurements to coincide with g11's or g12's
measurement, I would not say that g11 is the "set in stone"
measurement.<br>
<br>
<span style="font-family: 'Helvetica Neue';" class=""></span>
<pre class="moz-signature" cols="72">BR
MK
----------------------------------------
Michael C. Kunkel, PhD
Forschungszentrum Jülich
Nuclear Physics Institute and Juelich Center for Hadron Physics
Experimental Hadron Structure (IKP-1)
<a class="moz-txt-link-abbreviated" href="http://www.fz-juelich.de/ikp">www.fz-juelich.de/ikp</a></pre>
<div class="moz-cite-prefix">On 7/26/15 8:00 PM, Volker Crede wrote:<br>
</div>
<blockquote cite="mid:FF91ED4F-7CC4-490C-BAF6-579364FA1DBF@fsu.edu"
type="cite">
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<div class="">Hi Everybody,</div>
<div class=""><br class="">
</div>
<div class="">I know that we are all working on finalizing various
g12 analyses. However, we found a serious issue with our <span
style="font-family: 'Helvetica Neue';" class="">γp </span><span
style="font-family: 'Lucida Grande';" class="">→</span><font
class="" face="Helvetica Neue"> pω cross section that
currently prevents us from moving on. We are somewhat stuck
and it may affect the whole run group. </font></div>
<div class=""><font class="" face="Helvetica Neue"><br class="">
</font></div>
<div class=""><font class="" face="Helvetica Neue">The attached
pictures show</font> the 3π invariant mass for the energy
range 1650 - 1700 MeV and for forward angles of the <span
style="font-family: 'Helvetica Neue';" class="">3</span>π
system. A nice <font class="" face="Helvetica Neue">ω peak is
visible and a massive hole on the right side of the peak. This
hole is not supposed to be there (unless somebody has a good
physics argument). The energy range is probably very low for
most of the g12 analyses. However, the hole will slowly move
to higher masses with increasing photon energy but it will not
disappear. The other two pictures show the same distribution
if one (1) uses events where only sectors 1, 3, 5 triggered or
alternatively, (2) only sectors 2, 4, 6 triggered. </font></div>
<div class=""><font class="" face="Helvetica Neue"><br class="">
</font></div>
<div class=""><font class="" face="Helvetica Neue">We assume the
effect is based on track inefficiencies, perhaps dead regions
in the drift chamber. In principle, Michael Kunkel’s "trigger
map" should account for this since his approach is based on
comparing two- and three-track events, i.e. it combines
trigger and track inefficiencies; the idea is good. </font><font
class="" face="Helvetica Neue">In our analysis however, this
trigger map leads to an overall disagreement with the g11 </font><span
style="font-family: 'Helvetica Neue';" class="">ω cross
section, whereas Zulkaida's current cross section is in fair
agreement with g11 but exhibits certain problematic regions,
e.g. the forward direction. These holes in the mass
distributions are not accounted for by the Monte Carlo
simulations and we assume the effect is not in the MC.</span></div>
<div class=""><br class="">
</div>
<div class=""><font class="" face="Helvetica Neue">We have a few
questions we would like some help with (and need to find an
answer for).</font></div>
<div class=""><font class="" face="Helvetica Neue"><br class="">
</font></div>
<div class=""><font class="" face="Helvetica Neue">1) Since it is
still possible that the problem is at our end, would anybody
be able to reproduce this problem for us? The effect is so big
that even a quick and dirty look at it, will probably work.</font></div>
<div class=""><font class="" face="Helvetica Neue"><br class="">
</font></div>
<div class=""><font class="" face="Helvetica Neue">2) We tried to
knock out dead TOF paddles as suggested in the analysis note.
The paddle numbers are available in the data. However in the
Monte Carlo, the numbers appear to be available only for the
proton and not for the pions. Has anybody else noticed this
issue? How do others knock out the paddles in the MC? Or is
this done automatically? </font><span style="font-family:
'Helvetica Neue';" class="">It is difficult to do this based
on measured angles since two particles with the same polar and
azimuthal angles, one produced at the beginning of the target
and one at the end, may hit different TOF paddles. The g12
target was very long.</span></div>
<div class=""><font class="" face="Helvetica Neue"><br class="">
</font></div>
<div class=""><font class="" face="Helvetica Neue">3) The Monte
Carlo “gpp" options given in the analysis note do not
reproduce the holes in the mass distributions. For this
reason, we do not know if dead wires are actually simulated
and to what extent. Can anybody comment on this?</font></div>
<div class=""><font class="" face="Helvetica Neue"><br class="">
</font></div>
<div class=""><font class="" face="Helvetica Neue">This problem
shows up in the </font><span style="font-family: 'Helvetica
Neue';" class="">γp </span><span style="font-family: 'Lucida
Grande';" class="">→</span><font class="" face="Helvetica
Neue"> pω channel but we are concerned that it may also affect
the two-pion channel we are analyzing, perhaps not as holes in
mass distributions but as general track inefficiencies in
certain regions of the drift chamber. In the latter case, it
would extremely difficult to notice. </font><font class=""
face="Helvetica Neue">If so, it can potentially affect any
reaction that uses Monte Carlo for the acceptance correction.
My understanding is that we partially use the p</font><span
style="font-family: 'Helvetica Neue';" class="">ω and the K</span>Λ
cross sections to make sure that the g12 MC, trigger, etc. is
working correctly.</div>
<div class=""><font class="" face="Helvetica Neue"><br class="">
</font></div>
<div class=""><font class="" face="Helvetica Neue">Best wishes,</font></div>
<div class=""><font class="" face="Helvetica Neue"><br class="">
</font></div>
<div class=""><font class="" face="Helvetica Neue"><span class="Apple-tab-span" style="white-space:pre"> </span>Volker</font></div>
<div class=""><br class="">
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