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Thank you, Eugene, for the explanation. For the post-decay, I used evtgen and the Belle II decay configuration file which includes all PDG particles and their recorded decay mechanisms. I will check if Jon's eta decay file is different from the Belle II one.</div>
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tks ig</div>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> Primexd <primexd-bounces@jlab.org> on behalf of Eugene Chudakov via Primexd <primexd@jlab.org><br>
<b>Sent:</b> Friday, August 9, 2024 7:31 PM<br>
<b>To:</b> primexd@jlab.org <primexd@jlab.org><br>
<b>Subject:</b> [Primexd] About eta decays in MC</font>
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The eta->gamma+gamma decay is simple - isotropic in the eta CM frame. The 3-body decays are isotropic, but different from the phase space. One may look into the analysis note by Jon Zarling on the eta cross section. There is a package decay_evtgen which does
these decays. It reads in a hddm file and writes out a hddm file.</div>
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eta decays are turned off in bggen_upd. It sends etas to the output. The decays are left to GEANT(4). I am sure GEANT4 uses the right BRs, but not sure it does the 3-body decays right. GEANT3 did not. One may find it out, or may try to do the decays using decay_evtgen.</div>
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PS. PYTHIA uses a model for 3-body pseudoscalar decays.</div>
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Eugene</div>
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