MadGraph5_aMC@NLO

Cross section issue

Asked by alberto

I am generating the following process

a a > e+ e-

with the model sm. When I launch the run I set the option 2 (photon from proton). 10k events.

If I repeat the same run in the same conditions (same parameters), I get very different values for the cross section that are well outside the error MG5 gives me.

I can't understand the reason.

Thanks.

Cheers,

Alberto

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Olivier Mattelaer (olivier-mattelaer) said : 		#1

Hi,

Looks like our phase space integration methods fails to integrate correctly such process.

I have already tires to understand this for a similar process and the conclusion is that the only origin that I see is that our phase-space integration algorithms fails
to integrate such case in a efficient way leading to a wrong convergence of the grid and to large fluctuation (and to under-estimation of the error)

Nothing that we can do in a short time scale.

Cheers,

Olivier

On 20 Apr 2015, at 19:26, alberto <email address hidden> wrote:

> New question #265534 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/265534
>
> I am generating the following process
>
> a a > e+ e-
>
> with the model sm. When I launch the run I set the option 2 (photon from proton). 10k events.
>
> If I repeat the same run in the same conditions (same parameters), I get very different values for the cross section that are well outside the error MG5 gives me.
>
> I can't understand the reason.
>
> Thanks.
>
> Cheers,
>
> Alberto
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

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