Width computation not working since 2.5

Dear Hugo,

They are indeed a small bug: The message should not be printed anymore.

In the past a normal “launch” computation was only computing the width and create the param_card.
Since now we have must better way to compute the width and since many people was confuse about this behavior (i.e. the fact that we do not generate events).
We have move back to a normal event generation for the launch command.
Indeed it looks like we have to remove that message as well.

If you still want to use this old method of computation. you can run
launch -i (equivalently ./bin/madevent)
and then type “calculate_decay_widths”
and you will recover that mode.

Cheers,

Olivier

> On Jan 10, 2017, at 16:57, hprager <email address hidden> wrote:
>
> New question #434900 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/434900
>
> Hello,
>
> Since the release of version 2.5.1, I don't manage to compute the width of a particle using the syntax generate particleName > productOfDecay1 productOfDecay2 (e.g. generate t > w+ b). I still get the following warning:
>
> This command will create a new param_card with the computed width.
> This param_card makes sense only if you include all processes for
> the computation of the width. For more efficient width computation:
> see arXiv:1402.1178.
>
> and I see that the computation of the width worked:
>
> === Results Summary for run: run_01 tag: tag_1 ===
>
> Width : 1.492 +- 2.413e-09 GeV
> Nb of events : 10000
>
> but when I look for the new param_card in the Events/run_01 folder I only find the two files run_01_tag_1_banner.txt and unweighted_events.lhe.gz. I don't see a new param_card in the model folder either. Is the new param_card created in a new location or is that a bug?
>
> Regards,
> Hugo
>
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Thank you for your quick answer! And is the computation of the width with “calculate_decay_widths” only valid in the narrow-width approximation?

Best,
Hugo

Dear Hugo,

In that mode, we just perform the phase-space integration of the process/amplitude that you ask for.
The computation is based on the S-matrix formalism assuming that you can have an asymptotic free state.

Cheers,

Olivier

> On Jan 11, 2017, at 10:19, hprager <email address hidden> wrote:
>
> Question #434900 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/434900
>
> Status: Answered => Open
>
> hprager is still having a problem:
> Thank you for your quick answer! And is the computation of the width
> with “calculate_decay_widths” only valid in the narrow-width
> approximation?
>
> Best,
> Hugo
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Thank you for your answer Olivier, this solves my problem.

Best,
Hugo