# on-shell

Asked by said ghourmin on 2021-03-16

Hi
what i'm denote in Madgraph is when masses of final particles is large than initial particle mass, for example Higgs decay to gauge boson ( h > z z ), when i operate launch to generate event nothing generate i received this message on the screen "Zero result detected: No Phase Space. Please check particle masses." . how i can make this process generate be possible to generate event if is possible

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2021-03-16
 Olivier Mattelaer (olivier-mattelaer) said on 2021-03-16: #1

Well conservation of energy is important.
since the mass of the higgs is smaller than twice the mass of the Z, that decay with two onshell Z is impossible.
and consequently this is not a Mg5aMaC limitation but a physics limitation.

So you need to move to a four-body decay here such that both Z can off-shell.
(or if you are not interested in the SM, you can also change the Z mass)

Cheers,

Olivier

> On 16 Mar 2021, at 12:06, said ghourmin <email address hidden> wrote:
>
> New question #696083 on MadGraph5_aMC@NLO:
>
> Hi
> what i'm denote in Madgraph is when masses of final particles is large than initial particle mass, for example Higgs decay to gauge boson ( h > z z ), when i operate launch to generate event nothing generate i received this message on the screen "Zero result detected: No Phase Space. Please check particle masses." . how i can make this process generate be possible to generate event if is possible
>
> --

 said ghourmin (saidghourmin) said on 2021-03-16: #2

Thank you

‫في الثلاثاء، 16 مارس 2021 في 11:20 ص تمت كتابة ما يلي بواسطة ‪Olivier

>
>
> Olivier Mattelaer proposed the following answer:
> Well conservation of energy is important.
> since the mass of the higgs is smaller than twice the mass of the Z, that
> decay with two onshell Z is impossible.
> and consequently this is not a Mg5aMaC limitation but a physics limitation.
>
> So you need to move to a four-body decay here such that both Z can
> off-shell.
> (or if you are not interested in the SM, you can also change the Z mass)
>
> Cheers,
>
> Olivier
>
> > On 16 Mar 2021, at 12:06, said ghourmin <
> >
> > New question #696083 on MadGraph5_aMC@NLO:
> >
> > Hi
> > what i'm denote in Madgraph is when masses of final particles is large
> than initial particle mass, for example Higgs decay to gauge boson ( h > z
> z ), when i operate launch to generate event nothing generate i received
> this message on the screen "Zero result detected: No Phase Space. Please
> check particle masses." . how i can make this process generate be possible
> to generate event if is possible
> >
> > --
>
> --
> know that it is solved:
>
>
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