MadGraph5_aMC@NLO

Preserving non-zero resonance width when doing decays in parton-shower

Asked by Josh Bendavid

In some complex BSM decay chains, doing all of the resonance decays with decay chain syntax or with madspin could be very slow. Though of course this neglects spin correlation/polarization effects, doing the decays in the parton shower is much faster in some cases.

At the moment (as a trivial example) if one does
generate p p > w+
and then decays the w in pythia, the W will be exactly on shell in every event (as it is in the lhe file).

Is it possible to generate the lhe files such that the w is undecayed by still properly samples the breit-wigner distribution at least?

Thanks,
Josh

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Olivier Mattelaer (olivier-mattelaer) said : 		#1

Hi Josh,

This is not possible.

Cheers,

Olivier

On 29 Apr 2015, at 07:37, Josh Bendavid <email address hidden> wrote:

> New question #266085 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/266085
>
> In some complex BSM decay chains, doing all of the resonance decays with decay chain syntax or with madspin could be very slow. Though of course this neglects spin correlation/polarization effects, doing the decays in the parton shower is much faster in some cases.
>
> At the moment (as a trivial example) if one does
> generate p p > w+
> and then decays the w in pythia, the W will be exactly on shell in every event (as it is in the lhe file).
>
> Is it possible to generate the lhe files such that the w is undecayed by still properly samples the breit-wigner distribution at least?
>
> Thanks,
> Josh
>
> --
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