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

From: Joseph Comfort <>
Date: Sun, 10 Nov 2013 10:46:25 -0700 (MST)

Dear Alfredo and Paola,

I have a least a partial answer to the question about insufficient yield
of etas: momentum (energy) range.

I found some old neutron files used in the old experiment to describe the
neutron beam at the entrance to the detector. Applying them to the case
and routines I sent you, the distribution in the pi0/eta figure I sent was
essentially reproduced (in Fluka, w/o Geant3). The etas even had the
correct mass of ~547 MeV! The neutron momenta that produced the etas
(and most pi0s) were mostly in the range 8-11 GeV/c.

The neutron spectrum was peaked at very low energies, but was relatively
flat out to near the maximum of ~15 GeV/c. It falls off rather steeply in
the current experiment, and is much better collimated, which will greatly
improve the BG situation.

Nevertheless, people in the collaboration have indicatons of problems with
etas in our early data. Small effects can matter.

1) Does Fluka have eta producing mechanisms for photons? Test
calculations showed none, even for pi0s. Do extensions exist for
Jefferson Lab, MAMI,...?

2) We will need to know where etas are produced in our detector and their
decay modes, to help determine if they pose significant concerns. Can you
please guide me to the places in the code where they are produced and
given a decay mode.

Thank you,
Joe Comfort

On Wed, 6 Nov 2013, Joseph Comfort wrote:

> Dear Alfredo and Paula,
> In the older experiment, the neutron flux was ~40 times the K0L flux, and I
> would not expect a K0L to produce an eta directly (s <-> d). The K0Ls were
> also pretty well collimated, while the neutrons had a substantial halo that
> would hit detector components.
> I don't have the photon flux handy, but I'm sure it was comparable to or
> larger than the neutrons (as in the current expt.). So photons are a
> possibility. Are such mechanisms in Fluka? The fact that the neutron
> hypothesis MC agrees so well with the data seemed to convince most of us that
> it was probably valid.
> To check, I ran K0L on the Al target. I got >260K pi0s and 38 events with
> masses between 475-480 MeV (the Fluka eta mass). (Sorry, I was actually
> using 3 GeV/c for my beams.) The yields will depend on the geometry which,
> in my case, are set for our current situation.
> In case I am doing something wrong, I am attaching the input and fortran
> files I am using. The Targ2 and Targ3 are meant for future studies and are
> inactive here. The Al target is set for 1 cm, but would best be changed to 5
> cm for LH2.
> Joe
> --
> Joseph Comfort Phone: (480)-965-6377
> Physics Department Dept.: (480)-965-3561
> Arizona State University Fax: (480)-965-7954
> Tempe, AZ 85287-1504 Email:
Received on Sun Nov 10 2013 - 19:55:07 CET

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