[Solid_software] Neutral Meson Generation

[Rakitha Sanjeewa Beminiwattha]

Hi Seamus,
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.
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.

Regards!


Rakitha Beminiwattha
Assistant Professor of Physics
Office: Engineering Annex 210
Louisiana Tech University
Tel No. 318 257 2435
https://orcid.org/0000-0002-1473-1651

On Mon, Apr 24, 2017 at 9:52 AM, Seamus Riordan <riordan at jlab.org> wrote:

> Hi everyone,
>
> I know the following is deprecated since we've abandoned Wiser, but I felt
> compelled to at least get some correct intuition established.
>
> I did some more exploration on how we calculate neutral mesons from
> Wiser and I'm not satisfied with what was in there.  The argument I was
> making that pion rates should be equal between flavors because deuterium
> is isospin 0 was a bad argument (my apologies to Rich).  From the
> standard Clebsch Gordan coefficient argument, pi0 = 2pi+ for
> gamma p -> Delta -> Npi (you can see this approximately holds in MAID
> for the P33).  This means for deuterium under that symmetry pi0 should
> be a factor 4 larger than pi+ (or pi-) instead of equal as we had
> it.  I corrected the eicRate SVN for completeness though no one should
> still be using it.
>
> I saw the K0 rates followed a similar logic, though the channels for
> production are very different.  I played around on Kaon MAID and looking
> at gamma p -> hyperon K, if you take Lambda and Sigma production to be
> the main channels, K0 production was a factor 4 smaller than K+ (K+ L
> and K+ S0 being about equal) which one might guess from simple quark
> content arguments.  I didn't touch this part of the code for now.
>
> I know it's not being used anymore, but I wanted to be complete.
>
> Best,
> Seamus
>
> --
> Seamus Riordan                          sriordan at anl.gov
> Argonne National Laboratory             Office: (630) 252-4101
> Assistant Physicist                     Fax:    (630) 252-3903
>
> Physics Division Building 203           Room C265
> Argonne National Laboratory
> 9700 S. Cass Ave
> Argonne, IL  60439
>
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