Re: [fluka-discuss]: eta(550) decays

From: Joseph Comfort <Joseph.Comfort_at_asu.edu>
Date: Mon, 4 Nov 2013 00:35:16 -0700 (MST)

Dear Giuseppe,

I returned from a collaboration meeting in which there was discussion of
the importance of understanding the eta meson background in our
experiment. With no guidance on how to get the information I want from
Fluka (the coordinates of eta production, by what mechanism, and how they
decay), I dug into the code. It is very intertwined reflecting, I guess,
a complex history.

There are several peculiarities.
1) In bdpart.f, the properties of etas are given to 2 code numbers, 29 and
31, although 31 appears to be the one that is used (and is not a 'user'
particle).
2) There is an ETA550 for code 31, and also an ETA547 with code 112. Why?
3) In hadden.f, the ETA550 is given a mass 0.48 GeV. Why?
4) Can etas be produced by photons? There are (gamma,pi0) data. There
are also (gamma,eta) data -- some very recent. We think most of our BG
comes from neutrons, but there are plenty of photons available as well.

I have not yet clearly identified where etas are produced in the code and
how the decay mode is selected, but I think I am close. We will need to
consider production by neutrons, mesons (e.g., pioms), and even photons
in materials.

I have set up some simple cases to see if Fluka actually produces etas,
specifically with decay into 2 photons (the real BG for us). I tried a
case for pi- on a liquid hydrogen (LH2) slab. There were plenty of pi0s
and also some etas -- the latter at 0.48 GeV! I also tried 3-GeV/c
neutrons on an aluminum slab, but there were no pi0s or etas (in 10^7
events). But we have data that shows both, and this is the starting point
of our concerns. A total absence in Fluka is disturbing, but maybe it is
just a matter of cross section.

Any guidance you can provide will be very helpful.

Thank you,
Joe Comfort
Received on Mon Nov 04 2013 - 09:29:43 CET

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