<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
<style type="text/css" style="display:none;"> P {margin-top:0;margin-bottom:0;} </style>
</head>
<body dir="ltr">
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
Sasha, you are correct. <br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
The full sample corresponds to 414M photons launched with an energy above 8GeV i.e. I did expect to see at least one hit for an eta-candidate below 1 degree. What is seen is 10's of etas above 1 degree (see fig. below after all selection criteria is applied).
So either the beamline implemented in Geant3/4 is not realistic and/or the Geant4 physics list is not appropriate for what we want to simulate.
<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
<img size="43746" contenttype="image/png" style="max-width: 100%; user-select: none;" unselectable="on" tabindex="-1" data-outlook-trace="F:1|T:1" src="cid:6c39a37d-2674-40a6-b49a-d147efcb3767"></div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
Without the elasticity cut, the diphoton invariant mass looks like this: it is cleaner than the data ...<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
<img size="42751" contenttype="image/png" style="max-width: 100%; user-select: none;" unselectable="on" tabindex="-1" data-outlook-trace="F:1|T:1" src="cid:bc7627fc-f681-4e65-96d4-75a13098ac29"><br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
But for this sample I place the photon beam 2 m upstream the target. Now, I am producing 4B photons with an energy above 8GeV ~22 m upstream from the target i.e. at the GlueX cave collimator.</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
tks ig.<br>
</div>
<div id="appendonsend"></div>
<hr style="display:inline-block;width:98%" tabindex="-1">
<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> Alexander Somov <somov@jlab.org><br>
<b>Sent:</b> Tuesday, March 16, 2021 7:09 PM<br>
<b>To:</b> Igal Jaegle <ijaegle@jlab.org>; primexd@jlab.org <primexd@jlab.org><br>
<b>Subject:</b> Re: Beamline background MC simulation & meeting tomorrow</font>
<div> </div>
</div>
<style type="text/css" style="display:none">
<!--
p
{margin-top:0;
margin-bottom:0}
-->
</style>
<div dir="ltr">
<div style="font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12pt; color:rgb(0,0,0)">
Thanks Igal,
<div><br>
</div>
<div>If I understand you correctly, this sample is statistically </div>
<div>insignificant. Your generated samples is worth of a second </div>
<div>compared with the typical run time of hours.</div>
<div><br>
</div>
<div>Just on the example of the empty target run:</div>
<div><br>
</div>
<div>The photon flux equivalent to all empty target runs is </div>
<div>~2.4 x 10^12 (with E_gamma > 8 GeV). For all production runs </div>
<div>it's several times larger.</div>
<div><br>
</div>
<div>The total number of runs in PrimEx is ~420; you processed</div>
<div>10^6 events for each run, i.e., 4.2 x 10^8 events in total (?)</div>
<div><br>
</div>
<div>If you reconstruct 1000 empty-target BG events below 1 degree </div>
<div>(as an example), the average production rate is 1 event per 2.4 x 10^9 photons.
</div>
<div>You need ~5 more samples like this to see at least one bg event </div>
<div>in the empty target run (on average).</div>
<div><br>
</div>
<div>(I guess that your bg is less than 1000 events below one degree).</div>
<div><br>
</div>
<div>The background might also be a combination of the em and hadronic events.</div>
<div><br>
</div>
<div>You need many more samples like this to exclude the em bg (if I understood </div>
<div>you correctly).</div>
<div><br>
</div>
<div><br>
</div>
<div>Cheers,</div>
Sasha<br>
</div>
<div id="x_appendonsend"></div>
<hr tabindex="-1" style="display:inline-block; width:98%">
<div id="x_divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" color="#000000" style="font-size:11pt"><b>From:</b> Primexd <primexd-bounces@jlab.org> on behalf of Igal Jaegle <ijaegle@jlab.org><br>
<b>Sent:</b> Monday, March 15, 2021 8:38 AM<br>
<b>To:</b> primexd@jlab.org <primexd@jlab.org><br>
<b>Subject:</b> [Primexd] Beamline background MC simulation & meeting tomorrow</font>
<div> </div>
</div>
<style type="text/css" style="display:none">
<!--
p
{margin-top:0;
margin-bottom:0}
-->
</style>
<div dir="ltr">
<div style="font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12pt; color:rgb(0,0,0)">
All,</div>
<div style="font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12pt; color:rgb(0,0,0)">
<br>
</div>
<div style="font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12pt; color:rgb(0,0,0)">
The first batch of background produced along the beamline can be found here:</div>
<div style="font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12pt; color:rgb(0,0,0)">
/cache/halld/gluex_simulations/PRIMEX/primex-beam-line-bkg-batch01-15032021</div>
<div style="font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12pt; color:rgb(0,0,0)">
<br>
</div>
<div style="font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12pt; color:rgb(0,0,0)">
In this batch, 1M photons with an energy above 8 GeV and following the DB flux distributions are shot upstream the target for each run with an entry for the flux in the DB. There are no entries below 1 degree for all runs combined (Be, He, empty targets). All
the entries above 1 degree correspond to hadronic processes (following the SAID DB) producing pi0/eta/etaprime. It is not clear if the physics list is adapted for what we want to simulate.
<br>
</div>
<div style="font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12pt; color:rgb(0,0,0)">
<br>
</div>
<div style="font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12pt; color:rgb(0,0,0)">
Also, the meeting will be short as we have an 11 am GlueX Physics Meeting. Note, Sasha and I might be a little bit late as we have a mandatory meeting between 9:30 and 10:30 am.<br>
</div>
<div style="font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12pt; color:rgb(0,0,0)">
<br>
</div>
<div style="font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12pt; color:rgb(0,0,0)">
tks ig.<br>
</div>
</div>
</div>
</body>
</html>