MC Format for GlueX (fwd)

[Elke-Caroline Aschenauer <elke@jlab.org>]

---------- Forwarded message ----------
Date: Fri, 20 Jun 2008 09:51:23 -0400
From: Matthew Shepherd <mashephe@indiana.edu>
To: Dan Dale <dale@athena.physics.isu.edu>, Liping Gan <ganl@uncw.edu>,
     Ashot Gasparian <gasparan@jlab.org>
Cc: Elke Aschenauer <elke@jlab.org>, Curtis Meyer <cmeyer@ernest.phys.cmu.edu>
Subject: MC Format for GlueX


Hi Dan, Liping, and Ashot,

I enjoyed our meeting yesterday.  As we mentioned it will be important
to start doing some simulations with the full MC.  In particular it
seems like we need samples of:

- eta Primakoff production
- inclusive eta production with rare decays

On our side we have two generators:

1.  A PYTHIA-based generator to generate inclusive hadronic
photoproduction at 12 GeV.  This generates the roughly 120 microbarn
photoproduction cross section.  We should generate a very large sample
of this background and then scale both your rare decays and Primakoff
production appropriately for the cross section. This will give a feel
for the expected backgrounds.

2.  We also use a GEANT simulation of the full beamline to generate
all of the beam related electromagnetic background.  Again we will
generate a large sample get get a feel for what this background looks
like.

 From you we will need the signal samples.  We can just use a simple
ASCII format.  Here are two example events.  These turn out to be b1
pi p final states so 5 pions and a proton.

9000 1 6
1 8 0.137
    1 -0.33816 -0.199603 1.50846 1.56474
2 9 0.137
   -1 0.0592538 -0.0287174 0.270175 0.309998
3 7 0.135
   0 0.125819 -0.0498192 0.20477 0.280122
4 8 0.137
   1 -0.117507 0.288612 1.31965 1.36284
5 7 0.135
   0 0.143892 -0.446216 5.27102 5.29355
6 13 0.93926
   0 0.126703 0.435744 0.425928 1.12674
9000 2 6
1 8 0.137
    1 0.044592 -0.405405 2.03381 2.07882
2 9 0.137
   -1 0.18331 -0.329839 1.50143 1.55418
3 7 0.135
   0 -0.199553 -0.0217402 1.35894 1.38031
4 8 0.137
   1 0.191079 0.512605 2.96586 3.019
5 7 0.135
   0 -0.226428 0.118279 0.875205 0.921666
6 13 0.93929
   0 0.00699956 0.126101 0.264746 0.984026

You may guess the format:

run event no_particles
particle_index particle_id mass
charge px py pz E

Here the particle ID is according to the standard particle numbering
scheme found in GEANT and PDG.  For the rare eta decays please go
ahead and decay the eta appropriately (write out the 4-vec's for the
pi^0 and two gammas) since GEANT will not know how to do this.

Once we have this, we can run the events through our simulation.

I think the next natural step then is to do a little analysis.  To cut
down on the learning curve a little, we can initially provide a ROOT
file that includes reconstructed information.  This would be just a
variable length array that contains the reconstructed four vectors of
all photons in the forward calorimeter in the event.  From there you
should be able to create invariant mass and angular distributions.

-Matt