Can I trust in the cross section?

Hi,

The difference between the two process is that in the second case, you have cut in the final state and not in the first case.
You might have a soft singularity in the first case which is not suppress by your cut.

Cheers,

Olivier

On 07 Jan 2015, at 08:11, Liucheng Wang <email address hidden> wrote:

> New question #260269 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/260269
>
> Hello,
>
> Before asking this question, I have read the answer of the existing question (https://answers.launchpad.net/mg5amcnlo/+question/255057).
> I am not sure whether my case is also caused by the efficiency of generating events in the case of VBF.
>
> I am using the updated version MG5_v2.2.2.
> My question can be simplified as two processes:
>
> 1) generate ve b > e- w+ b , standard model, tree level, 10000 events, default settings of all parameters except PDF=0 for two initial states:
> 0 = lpp1 ! beam 1 type
> 0 = lpp2 ! beam 2 type
> 6500 = ebeam1 ! beam 1 total energy in GeV
> 6500 = ebeam2 ! beam 2 total energy in GeV
> The result is : Cross-section : 10.3 +- 0.4252 pb
> Nb of events : 438
>
> 2) generate ve d > e- w+ d , standard model, tree level, 10000 events, default settings of all parameters except PDF=0 for two initial states:
> 0 = lpp1 ! beam 1 type
> 0 = lpp2 ! beam 2 type
> 6500 = ebeam1 ! beam 1 total energy in GeV
> 6500 = ebeam2 ! beam 2 total energy in GeV
> The result is : Cross-section : 0.09554 +- 0.0002541 pb
> Nb of events : 10000
>
> You can see that I only got 438 events in the first process.
> Do you think the cross-section 10.3 pb is physical and I can trust in it ?
> Compared to the second process, the cross-section 10.3 pb looks weird to me.
>
> Thank you.
>
> --
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> contact for MadGraph5_aMC@NLO.

Hi Olivier,

Your suggestion is very useful.
Thank you.