Fail to reach target "event number"

Asked by Yudong Wang on 2019-11-28

By using Feynrules, I create a new model which add a new vertex “ta mu a” into Standard Model.
I import this model and generate the process "e+ e- > ta+ ta-, ta- > mu- a".
However, I only get 1 event( nevents = 10000 in the run_card.dat) and there is information that "INFO: fail to reach target 10000".
How to solve this problem?

Question information

Language:
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Status:
Solved
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MadGraph5_aMC@NLO Edit question
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Solved by:
Yudong Wang
Solved:
2019-11-29
Last query:
2019-11-29
Last reply:
2019-11-28

Hi,

What is the width of the tau?
If it is zero (My guess is that this is the case) then your cross-section is infinite for such process and it is impossible to generate more than one event.

This being said, it is likely that the physical width of the tau would be too small for madgraph to handle it correctly numerically. Consequently madgraph will automatically use a much larger width for the phase-space integration (1e-8 times the tau mass) to avoid numerical issue

Cheers,

Olivier

> On 28 Nov 2019, at 09:53, Yudong Wang <email address hidden> wrote:
>
> New question #686334 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/686334
>
> By using Feynrules, I create a new model which add a new vertex “ta mu a” into Standard Model.
> I import this model and generate the process "e+ e- > ta+ ta-, ta- > mu- a".
> However, I only get 1 event( nevents = 10000 in the run_card.dat) and there is information that "INFO: fail to reach target 10000".
> How to solve this problem?
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Yudong Wang (wyd1216) said : #3

Hi,
The problem is resolved as you described.
I give the tau a larger decay width and I get the events number which I set in the run_card.dat.
Thank you vary much.

best,
yudongw