Cannot decay POWHEG t-ch 4FS events with MadSpin

Dear Riccardo,

The main problem is that the default SM model in MadGraph assumes diagonal CKM. (which is perfectly valid for MC generation)
If you make such assumptions, then such initial/final state do not exists.
So you need to change the model that you “claim” using for one with non diagonal CKM.

Cheers,

Olivier

> On Jun 7, 2016, at 20:02, Riccardo Di Sipio <email address hidden> wrote:
>
> New question #295026 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/295026
>
> Hi,
>
> I'm trying to decay events generated with POWHEG t-channel 4FS using MadSpin. Looking at the documentation, I set in the header the following "mockup" process:
>
> generate p p > t b~ j $$ w+ w- [QCD]
>
> Then, in MadSpin, I specify:
> decay t > w+ b, w+ > all all
> decay t~ > w- b~, w- > all all
>
> However, the program crashes because of the following error:
>
> Command "launch" interrupted with error:
> KeyError : ((2, 21), (-5, 3, 6, 21))
>
> Looking at the LHE file, I see that the events have an extra parton, originating from initial- or final-state radiation, e.g.:
>
> <event>
> 6 10000 1.98238E+02 1.07900E+01 -1.00000E+00 1.94675E-01
> 21 -1 0 0 511 502 0.000000000E+00 0.000000000E+00 6.922772374E+01 6.922772374E+01 0.000000000E+00 0.00000E+00 9.000E+00
> 2 -1 0 0 510 0 0.000000000E+00 0.000000000E+00 -3.149643439E+03 3.149643439E+03 0.000000000E+00 0.00000E+00 9.000E+00
> 6 1 1 2 501 0 -5.683771526E+01 2.746316291E+01 -8.843891419E+01 2.038686899E+02 1.725000000E+02 0.00000E+00 9.000E+00
> -5 1 1 2 0 502 1.842432487E+01 7.005096912E+00 -1.389630809E+01 2.461984988E+01 4.950000000E+00 0.00000E+00 9.000E+00
> 3 1 1 2 510 0 3.625666291E+01 -2.389602035E+01 -2.979216561E+03 2.979532997E+03 4.315837288E-05 0.00000E+00 9.000E+00
> 21 1 1 2 511 501 2.156727472E+00 -1.057223948E+01 1.136068099E+00 1.084962542E+01 5.853330893E-07 0.00000E+00 9.000E+00
> #pdf 21 2 0.97277306E-02 0.48377792E+00 0.81008716E+02 0.81224666E+01 0.12321520E+00
> </event>
>
> So I modified the header in order to specify a 2->4 process:
> generate p p > t b~ j j $$ w+ w-
>
> But I still get the same error:
> KeyError : ((2, 21), (-5, 3, 6, 21))
>
> Am I missing something?
> Thank you in advance,
> Riccardo
>
>
>
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Hi,

  thanks a lot for the clarification, this solved the problem.

Cheers,
Riccardo