low energy neutrino proton scattering

The "issue" is actually the running scale of MG5aMC.
When set to "-1", we do have a security that if the running scale is smaller than 4 Gev^2 then the event is discarded (since you are in the non perturbative regime). This is likely your issue here.

You can either set yourself to a fix scale and/or use another dynamical scale choice.
Note that the code has issue if your scale is too small since at some point the running of alpha_s starts to badly behaves.

Cheers,

Olivier

> On 22 Jun 2023, at 19:10, Sam Carey <email address hidden> wrote:
>
> New question #707074 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/707074
>
> Dear Expert,
> I'be been trying to generate the cross-section for the process vm p > vm p a for a proton at rest and neutrino energies in the range [1,10] GeV. But there seems to be a minimum neutrino energy (about 5 GeV) before I start seeing output. Below this I get a zero cross-section.
> Here is the error message:
> Survey return zero cross section.
> Typical reasons are the following:
> 1) A massive s-channel particle has a width set to zero.
> 2) The pdf are zero for at least one of the initial state particles
> or you are using maxjetflavor=4 for initial state b:s.
> 3) The cuts are too strong.
> Please check/correct your param_card and/or your run_card.
>
> p.s. I have removed also removed all the cuts
>
> --
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