Does Pythia8 use an internally set parameter that uses externally set ones?

Asked by Mohamed Aly on 2020-06-01

Hi,

I am currrently wanting to calculate some decay widths internally using the values of externally set parameters in the model. I read in:
 https://answers.launchpad.net/mg5amcnlo/+question/296282
that the parameter card will NOT be updated with the computed value of the width, but the computed value is the one used for the rest of process generation.

In the above thread, it was also mentioned that pythia8 will not use the new value. I was wondering if there is a way to ensure that pythia8 takes into account the new value ? Do you know if the width enters the algorithm for pythia8 showering (i.e. how much do I need to worry that the correct value is not being used) ?

Thank you very much,
Mohamed

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Last query:
2020-06-01
Last reply:
2020-06-02

Dear Mohamed,

This is an old question/answer.

We are now TRYING to update the param_card automatically to update such value in the param_card.
They are however cases when this is not possible (and in that case you will see a warning).
To be sure at 100% is to check the value printed within pythia obviously (or the one in the banner of the run -- which is slightly less secure--)

> Do you know if the width enters the algorithm for pythia8 showering (i.e. how much do I need to worry that the correct value is not being used) ?

Pythia8 can do a lot of stuff. But some of those algorithm can use the width (and many does not)

Cheers,

Olivier

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