crossection of subprocess is smaller than the whole

Hi Von,

Such type of problem are typically due to the value of the width which is not set correctly in your param_card.
Did you compute/have the correct value of the width?
If you didn’t do it, then one solution is to use MadWidth:arXiv:1402.1178
Using that code is actually very easy:
you just have to set “Auto” for the value of the width and MadGraph will all MadWidth automatically.

Cheers,

Olivier

On Sep 13, 2014, at 2:33 PM, von <email address hidden> wrote:

> New question #254437 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/254437
>
> Hi,
>
> I am generatinggenerate
> p p > go go , go > t t~ n1 , go > t t~ n1
> to get the K factor,I need generate generate
> p p > go go
>
> but the first process comes with Cross-section :0.1739 +- 0.000258 pb(parton and hadron)
> while the second has Cross-section : 0.002487 +- 2.632e-06 pb(parton and hadron)
>
> the param_card.dat are the same,both are:
> all particles are decoupled,except for gluino with mass 1.15Tev,neutralino(n1) with mass 275Gev,and stop quark(t1),mass 650Gev
>
> and I found changing mass of t1 also changes the crossection
> when mass of t1 is 460Gev,the 4 top 2 MET process has Cross-section : 0.009056 +- 1.295e-05 pb
> when mass of t1 is 850Gev,the 4 top 2 MET process has Cross-section : 0.03881 +- 5.735e-05 pb
>
> best regards
>
> von
>
>
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