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

From: Alfredo Ferrari <alfredo.ferrari_at_cern.ch>
Date: Wed, 6 Nov 2013 14:45:39 +0100

Dear Joe

are you sure your BG is really due to eta's from neutrons?

A quick look into the PDG gives as possible baryon resonances decaying
into eta's only the N*(1520) with a tiny branching ratio of 2.3 10^-3
bracketed because highly uncertain, and the N*(1535) with a sizeable
branching. I'll comment later on the status of FLUKA event generators
wrt those resonances. Only, if I run 3 GeV (GeV, not GeV/c) neutrons
on Aluminum I get roughly 1 eta every 100 interactions, which could be
completely wrong (likely it is understimated) but not 0.

Were you speaking about n-Al or n-H?

              Ciao
             Alfredo

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| Alfredo Ferrari || Tel.: +41.22.76.76119 |
| CERN-EN/STI || Fax.: +41.22.76.69474 |
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On Tue, 5 Nov 2013, Joseph Comfort wrote:

> Hi Alfredo,
>
> Our experiment (KOTO) has a mixture of neutral beams (K0L, n, gamma),
> generally spread over a range of a few GeV and below, collimated from a
> production target.
>
> Specific cases I am testing at the moment include pi- on LH2 and neutrons on
> Al, both at 3 GeV. I get nice pi0 and eta peaks, with a sensible ratio, for
> pi-/LH2. I get pi0s, but no etas at all (exactly zero), for n/Al, even after
>> 10^8 beam particles and over 13,000 pi0s.
> The meson vertex is in the suitably thin target, and the particle is
> identified from the 2-gamma decay mode.
>
> The experiment is set to identify pi0s from K0Ls. However, a nasty BG mode
> comes from "halo" neutrons that hit some charged-particle veto detectors in
> front of the main photon detectors, producing etas. Unfortunately, the etas
> can reconstruct to look like legitimate pi0s.
>
> This BG was identified in an earlier version of the experiment, and studied
> by inserting an Al target in the beam path. A figure from a thesis is
> attached. The MC was produced from a Geant3-based code, and the
> normalization matches very well. But the current Fluka is not producing etas
> for this case.
>
> Most eta decay modes will get vetoed in the detector. Even without
> considering normalization, we need to study where etas are produced and,
> preferably, bias the decay to the 2-gamma mode.
>
> It is very clear to me, as you indicated, that major revisions to the code
> would be a huge task. I am instead looking for places where I can more
> simply tap in to determine the eta birth location and its decay mode. Being
> a Fortran person, I would prefer to stay with Fluka if possible.
>
> Thank you,
> Joe Comfort
>
Received on Wed Nov 06 2013 - 15:34:29 CET