branch ratios of W/Z in MadGraph

Asked by Yue Xu on 2020-08-17

Dear MadGraph experts,

I'm working with MadGraph and MadSpin. I wonder where I can find the default branch ratio values of W/Z decays.
Are there BRs as same as the one used in MadSpin?

Thanks,
Yue

Question information

Language:
English Edit question
Status:
Answered
For:
MadGraph5_aMC@NLO Edit question
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Last query:
2020-08-17
Last reply:
2020-08-17

MadGraph does not use narrow-width approximation and therefore does not use Branching Ratio.
You can specify the BR in the param_card if you want but those are not used (and therefore we do not have default for those).

MadSpin does use the narrow-width approximation for the total cross-section and therefore use the Branching Ratio.
If the Branching ratio is not specified in the param_card for ALL relevant particles, then we use this paper:
https://arxiv.org/abs/1402.1178 and limit the computation to two body decay (MadSpin)

We do not have any hardcoded value for the W/Z it all depends of the mass of those particles and of the model that you consider.
(even if everything is Standard Model). Consequently the BR will be LO accurate.

Cheers,

Olivier

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