Re: [fluka-discuss]: Question about neutrino production in FLUKA

From: Paola Sala <>
Date: Thu, 10 Dec 2020 13:18:36 +0100

Dera Andrea,
sorry for the late answer, maybe you found already -)
My impression is that you start with a largely different number of
positive and negative pions decaying at rest, that are then originating
low energy mu+ and mu- . This can bee seen by the monochrmatic peak at
30 MeV in the nu-mu and nu-mu-bar, the numu (pion+ -> mu+ numu) being
almost two orders of magnitude more than the num-bar (pion->mu- numubar).
This large difference reflects in the lfact that you get a lot of numubar
and nue fom the positive muon decay.

The few negative muons, all of them produce a nu_mu, either from decay or
when captured, two orders of magnitude less than numubar and nue from
Then, only the non-captured fraction produces a nuebar. From the plot, the
capture probability seems to be around 50%

Check it...
ah yes, the negative pions are preferentially interacting or being
captured by nuclei when at rest

> Dear all,
> I am using FLUKA to sample the neutrino production by a 11 GeV electron
> beam impinging on a thick target.
> I have a custom mgdraw.f code that samples (via entry BXDRAW) each
> neutrino passing through a plane, perpendicular to the beam axis,
> downstream the target.
> The following plot shows the neutrino current, in neutrinos / GeV /
> impigning_electron, where each color refers to a different neutrino
> species.
> In the low energy part of the spectrum (E < ~ 50 MeV), the continuous part
> of the distribution is due to the decay at rest of muons:
> mu- -> e- nu_mu nu_e_bar
> mu+ -> e+ nu_mu_bar nu_e
> I observe that nu_e and nu_mu_bar are produced with higher intensity than
> nu_mu and nu_e_bar, due to the fact that mu- can be captured by nuclei and
> give rise to mu- X(Z,A) -> nu_mu X(Z-1,A) (with the large peak in the
> nu_mu distribution at ~ 100 MeV).
> However, while the contribution of nu_e and nu_mu_bar is the same at low
> energy, this is not true for nu_mu and nu_e_bar.
> I do not understand why, since any time a mu- decays at rest, it will
> produce a nu_mu and a nu_e_bar. Here it seems there is a factor x2
> difference.
> Note that I am considering phase-space decays, hence the energy spectra
> for decay-at-rest are all the same.
> Thanks,
> Bests,
> Andrea

Paola Sala
INFN Milano
tel. Milano +39-0250317374
tel. CERN +41-227679148

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Received on Thu Dec 10 2020 - 15:30:01 CET

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