Unable to generate events for RPV stop decay

Hi Brett,

> . I have tried editing the STOPMIX block to have no mixing between the left and right stop (by setting either element 11 or 22 to 1 and the rest to 0), but this did not allow me to produce the events either.

I don’t see any definition of STOPMIX inside your UFO model, so this is not likely to do anything.
Therefore I remove your STOPMIX block for your param_card for all what follows.

I did the following
import model ReducedUFO
display interactions t1 b~ mu-
it returns me this:
Interactions 3766 : b~ mu- t1 has the following property:
{
    'id': 3766,
    'particles': [-5,13,1000006],
    'color': [1 T(2,0)],
    'lorentz': ['FFS1'],
    'couplings': {(0, 0): 'GC_5020'},
    'orders': {'QED': 1},
    'loop_particles': None,
    'type': 'base',
    ‘perturbation_type': None
}
then after pressing “q’
it shows me this:
3766 : b~ mu- t1

This shows that the interaction is define.

Then I do the following
cp param_card models/ReducedUFO/restrict_usercard.dat #note this is the card without STOPMIX
then I did:
import model ReducedUFO-usercard
display interactions t1 b~ mu-
and now it doesn’t return me anything.

This means that the coupling for t1 b~ mu- is at zero for your param_card and therefore it is impossible the associate cross-section for those decays are zero.

Cheers,

Olivier

On Mar 17, 2014, at 3:46 PM, Brett Jackson <email address hidden> wrote:

> New question #245629 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/245629
>
> Hello,
>
> I am trying to generate events for an RPV SUSY model, where the stop is allowed to decay to a b quark plus a lepton. A colleague provided me with a UFO model which included the decay of interest. I have managed to import the model into MadGraph 5, and generate diagrams for the decay of interest, but when I try to generate events, MadGraph tells me it has zero cross section. I get the following message at the end of the run:
>
> """
> INFO: End survey
> 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.
> """
>
> I was hoping someone would be able to provide some insight into the problem. I have posted the UFO model along with my proc/run/param cards to dropbox (https://www.dropbox.com/sh/ga5ntsjh4xybet6/3xtpCY_YSF).
>
> I have also tried generating stop pairs which remain un-decayed using this model, and I was able to successfully generate events. It is only when I try to decay the stops when the problems arise.
>
> My understanding is this model has no decay defined for a right handed stop. For the purposes of this study, we would like to focus on the left handed stop decays for now. I have tried editing the STOPMIX block to have no mixing between the left and right stop (by setting either element 11 or 22 to 1 and the rest to 0), but this did not allow me to produce the events either.
>
> Do you know of an scenario where I would be able to produce the diagrams associated with the decay of interest, but not events? Could there be a problem with the UFO? If so, is there a way for me to check this?
>
> Thank you in advance for your help!
>
> Cheers,
> -Brett
>
>
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