<div dir="ltr">Hi Seamus,<div>I saw excess a pi0 production in Geant4 at low photon momentum. I attached one of the talks I gave in a collaboration meeting, see slides 9 and 12. Anyway, we saw a disagreement with the isospin symmetry assumption for meson (pi0) production when compared with Geant4 but could not explain the reason. Also, I looked at some meson production data analysis results (see slide 17, plot on the right) but we did not see any large deviation from isospin assumption. I have not looked into this for some time now. </div><div>In Hall D generator we are using isospin assumption to approximate for the deuterium, which is just the sum of meson production from proton and neutron. In the Wiser generator, the meson production is just the sum/2 from proton and neutron.</div><div><br></div><div>Regards!</div><div><br></div></div><div class="gmail_extra"><br clear="all"><div><div class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div dir="ltr">Rakitha Beminiwattha<br>Assistant Professor of Physics </div><div dir="ltr"><font color="#000000" face="arial, helvetica, sans-serif" size="2">Office: Engineering Annex 210</font><br></div><div dir="ltr"><span style="font-size:12.8px">Louisiana Tech University</span><font color="#000000" face="times new roman"><span style="font-size:14.4px"><br></span></font></div><div dir="ltr">Tel No. 318 257 2435<br><a href="https://orcid.org/0000-0002-1473-1651" target="_blank">https://orcid.org/0000-0002-1473-1651</a><br></div></div></div></div></div></div></div></div>
<br><div class="gmail_quote">On Mon, Apr 24, 2017 at 9:52 AM, Seamus Riordan <span dir="ltr"><<a href="mailto:riordan@jlab.org" target="_blank">riordan@jlab.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Hi everyone,<br>
<br>
I know the following is deprecated since we've abandoned Wiser, but I felt<br>
compelled to at least get some correct intuition established.<br>
<br>
I did some more exploration on how we calculate neutral mesons from<br>
Wiser and I'm not satisfied with what was in there. The argument I was<br>
making that pion rates should be equal between flavors because deuterium<br>
is isospin 0 was a bad argument (my apologies to Rich). From the<br>
standard Clebsch Gordan coefficient argument, pi0 = 2pi+ for<br>
gamma p -> Delta -> Npi (you can see this approximately holds in MAID<br>
for the P33). This means for deuterium under that symmetry pi0 should<br>
be a factor 4 larger than pi+ (or pi-) instead of equal as we had<br>
it. I corrected the eicRate SVN for completeness though no one should<br>
still be using it.<br>
<br>
I saw the K0 rates followed a similar logic, though the channels for<br>
production are very different. I played around on Kaon MAID and looking<br>
at gamma p -> hyperon K, if you take Lambda and Sigma production to be<br>
the main channels, K0 production was a factor 4 smaller than K+ (K+ L<br>
and K+ S0 being about equal) which one might guess from simple quark<br>
content arguments. I didn't touch this part of the code for now.<br>
<br>
I know it's not being used anymore, but I wanted to be complete.<br>
<br>
Best,<br>
Seamus<br>
<br>
-- <br>
Seamus Riordan <a href="mailto:sriordan@anl.gov" target="_blank">sriordan@anl.gov</a><br>
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<br>
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