# neutrino momentum in the dynamic scale choice

Dear experts,

I see the definition of the dynamic scale choice =3, in setscales.f. However I have a question when I have a ttbar process in the dilepton channel, how the momentum of the neutrino is used?

1) pT(nu) + pT(nubar)

or

2) pT(nu+nubar)

Where I can find such information?
Choice =3, is the sum of the transverse mass of all final state particles divided by 2, right?

Thanks,
Mazuza

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2017-08-18
 Olivier Mattelaer (olivier-mattelaer) said on 2017-08-17: #1

Hi,

Here is the code associated: (SubProcesses/setscales.f line 69)

elseif(dynamical_scale_choice.eq.3) then
c sum of the transverse mass divide by 2
c m^2+pt^2=p(0)^2-p(3)^2=(p(0)+p(3))*(p(0)-p(3))
rscale=0d0
do i=3,nexternal
rscale=rscale+dsqrt(max(0d0,(P(0,i)+P(3,i))*(P(0,i)-P(3,i))))
enddo
rscale=rscale/2d0

Cheers,

Olivier

> On 17 Aug 2017, at 17:44, mazuza <email address hidden> wrote:
>
> New question #656446 on MadGraph5_aMC@NLO:
>
> Dear experts,
>
> I see the definition of the dynamic scale choice =3, in setscales.f. However I have a question when I have a ttbar process in the dilepton channel, how the momentum of the neutrino is used?
>
> 1) pT(nu) + pT(nubar)
>
> or
>
> 2) pT(nu+nubar)
>
> Where I can find such information?
> Choice =3, is the sum of the transverse mass of all final state particles divided by 2, right?
>
> Thanks,
> Mazuza
>
>
> --

 mazuza (mghneimat) said on 2017-08-18: #2

Hi Olivier,

I found those lines, but its not clear for me, in case of two neutrinos how is the transverse momentum treadted. Or its the same for all final particles, is summed separately?

Thanks,
Mazuza

 Olivier Mattelaer (olivier-mattelaer) said on 2017-08-18: #3

Hi,

All final state particles are include in the same way, i.e. they are summed separately.
Since this variable is not associated to an observable but to a (internal) scale, I do not see any good reason to have a different behaviour for lepton and neutrino on this matter.

Cheers,

Olivier

> On 18 Aug 2017, at 09:34, mazuza <email address hidden> wrote:
>
> Question #656446 on MadGraph5_aMC@NLO changed:
>
>
> mazuza is still having a problem:
> Hi Olivier,
>
> I found those lines, but its not clear for me, in case of two neutrinos
> how is the transverse momentum treadted. Or its the same for all final
> particles, is summed separately?
>
>
> Thanks,
> Mazuza
>
> --