NMSSM SM-like Higgs mass changes per event generated

Asked by Douglas Tuckler on 2021-06-02

Hello,

I am using the NMSSM model to generate a SM-like Higgs in association with a W-boson, followed by the a long decay chain for the Higgs. In particular, I generate the process:

p p > h02 w+, (h02 > n1 n2, (n2 > h01 n1, h01 > tau+ tau-))

In this case h02 is the SM-like Higgs so I set the parameter mh02 in the param_card to 125.0. I can see that this parameter is fixed to 125.0 when I looked at the begining of the unweighted_events.lhe file. However I am also seeing that for every event in the file the mass of the SM-like Higgs is changing. None of the masses of other particles (i.e h01, n1, n2) are changing on an event-by-event basis. Is this supposed to be happening? If I just run p p > h02 w+ and fix mh02 = 125.0, then I don't see this parameter varying per event.

Is there an issue with the syntax I use above to generate the full decay chain? Or is there something else going on inside of MadGraph that is making the mass of h02 change per event?

Any help is appreciated.
Thanks!

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Olivier Mattelaer (olivier-mattelaer) said :
#1

All virtual particle can be offshell and therefore the associate invariant mass is changing event by event.
This is control by the total width of the particle.

Cheers,

Olivier

> On 2 Jun 2021, at 22:10, Douglas Tuckler <email address hidden> wrote:
>
> New question #697357 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/697357
>
> Hello,
>
> I am using the NMSSM model to generate a SM-like Higgs in association with a W-boson, followed by the a long decay chain for the Higgs. In particular, I generate the process:
>
> p p > h02 w+, (h02 > n1 n2, (n2 > h01 n1, h01 > tau+ tau-))
>
> In this case h02 is the SM-like Higgs so I set the parameter mh02 in the param_card to 125.0. I can see that this parameter is fixed to 125.0 when I looked at the begining of the unweighted_events.lhe file. However I am also seeing that for every event in the file the mass of the SM-like Higgs is changing. None of the masses of other particles (i.e h01, n1, n2) are changing on an event-by-event basis. Is this supposed to be happening? If I just run p p > h02 w+ and fix mh02 = 125.0, then I don't see this parameter varying per event.
>
> Is there an issue with the syntax I use above to generate the full decay chain? Or is there something else going on inside of MadGraph that is making the mass of h02 change per event?
>
> Any help is appreciated.
> Thanks!
>
>
> --
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> contact for MadGraph5_aMC@NLO.

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