Hi:
I want to simulate the decay of Higgs to ZZ and WW. Since m_h < 2m_Z/2m_W, if I input the decay chain in MG, I need to give the whole chain like

generate p p > h h, ( h > w+ w-, w+ > l+ vl, w- > l- vl~), ( h > w+ w-, w+ > l+ vl, w- > l- vl~)

which is the 8 final states process, the MG takes long time to give me the required events.

However, I realize I can also use MadSpin to decay the Higgs. I guess the syntax should be for MG
generate p p > h h

decay h > w+ w-, w+ > l+ vl, w- > l- vl~

The generation of un-decayed events is fast, but still the MadSpin takes time to process all events.

Are these the only two ways to handle such off-shell decay?(Am I doing right for the above methods?) Or there is some other method that I can use to speed up the simulation?

Thanks!

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2018-09-20
 Olivier Mattelaer (olivier-mattelaer) said on 2018-09-04: #1

If you look at the invariant mass distribution of the W, you will see that they are quite bad.
SInce you ask both W to be onshell with this syntax.

> h > l+ vl l- vl~

h > w+ w- > l+ vl l- vl~
to force the presence of the w without asking them to be onshell

Cheers,

Olivier

> On 4 Sep 2018, at 20:52, teddym <email address hidden> wrote:
>
> New question #673342 on MadGraph5_aMC@NLO:
>
> Hi:
> I want to simulate the decay of Higgs to ZZ and WW. Since m_h < 2m_Z/2m_W, if I input the decay chain in MG, I need to give the whole chain like
>
> generate p p > h h, ( h > w+ w-, w+ > l+ vl, w- > l- vl~), ( h > w+ w-, w+ > l+ vl, w- > l- vl~)
>
> which is the 8 final states process, the MG takes long time to give me the required events.
>
> However, I realize I can also use MadSpin to decay the Higgs. I guess the syntax should be for MG
> generate p p > h h
>
> decay h > w+ w-, w+ > l+ vl, w- > l- vl~
>
> The generation of un-decayed events is fast, but still the MadSpin takes time to process all events.
>
>
> Are these the only two ways to handle such off-shell decay?(Am I doing right for the above methods?) Or there is some other method that I can use to speed up the simulation?
>
> Thanks!
>
> --

 teddym (niepanchongsheng) said on 2018-09-05: #2

Hi Olivier:
Thanks for fixing the syntax.
But it seems I can't use this in MadSpin, it returns:

INFO: generate e+ e- > z h, h > w+ w- > l+ vl l- vl~ QCD=99 --no_warning=duplicate;
Command "decay_events run_01" interrupted with error:
InvalidCmd : No matrix elements generated, check overall coupling orders

Does it mean that I can't decay the Higgs in this way in MadSpin?

Best!

 Launchpad Janitor (janitor) said on 2018-09-20: #3

This question was expired because it remained in the 'Open' state without activity for the last 15 days.

 Olivier Mattelaer (olivier-mattelaer) said on 2018-09-20: #4

Hi,

MadSpin can only do two body decay in the "normal" mode (full spin correlation + off-shell effects)
For the Higgs decay you can use the command "set spinmode none" (no spin correlation between production and decay and no offshell effect for the Higgs) to have it working

Cheers,

Olivier