HT cut for NLO

Asked by Josh McFayden on 2018-02-20

Hi all,
Sorry for such a naive question, but can someone give me an example cuts.f to apply a HT cut for an NLO sample?
I tried, but my fortran is essentially non-existent, so I didn't manage to get it to compile.
Best,
Josh

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MadGraph5_aMC@NLO Edit question
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Last query:
2018-02-20
Last reply:
2018-02-21
Josh McFayden (mcfayden) said : #1

(Preferably for v2.5.5 or v2.6.1)

Josh McFayden (mcfayden) said : #2

Ok, in the end I think I managed it myself:

      htmp=0d0

      do i=0,nexternal
         if(istatus(i).eq.1)then
            htmp=htmp+sqrt(p(1,i)**2+p(2,i)**2)
         endif
      enddo

      htparton=htmp

      if (htparton.lt.10d0)then
         passcuts_user=.false.
         return
      endif
      end

But, I still get a negative cross section:
      Total cross section: -1.183e+09 +- 1.3e+08 pb

Hi,

I did not try to compile the following but something like this shoud work:

(top of the function)
      double precision htj

(at the place dedicated to user cuts)
      htj=0d0
      do i=1,nexternal ! loop over all external particles
         if (istatus(i).eq.1 ! final state particle
     & .and. is_a_j(i)) then ! massless quark/gluon
 htj = htj + pt(p(0,i))
        enddo
        if (htj.lt.300d0)then
           passcuts_user=.false.
           return
        endif

Cheers,

Olivier

PS: Note that I do not use the fastjet clustering in this case, since this should be IR save.

> On 20 Feb 2018, at 10:31, Josh McFayden <email address hidden> wrote:
>
> Question #664670 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/664670
>
> Josh McFayden gave more information on the question:
> (Preferably for v2.5.5 or v2.6.1)
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Josh McFayden (mcfayden) said : #4

Thanks Olivier!
But unfortunately I still get a negative cross section (for an HT cut of 10 GeV)
      Total cross section: -7.772e+07 +- 2.2e+07 pb

Is there something else I can try?
Best,
Josh

If we look at setscales.f you have another method to define ht cut:

          htj=0d0
          do i=3,nexternal
            htj=htj+dsqrt(max(0d0,(pp(0,i)+pp(3,i))*(pp(0,i)-pp(3,i))))
          enddo

But I do not think that you are facing some cut definition, it should rather be related to some physics.

Cheers,

Olivier

> On 20 Feb 2018, at 22:07, Josh McFayden <email address hidden> wrote:
>
> Question #664670 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/664670
>
> Status: Answered => Open
>
> Josh McFayden is still having a problem:
> Thanks Olivier!
> But unfortunately I still get a negative cross section (for an HT cut of 10 GeV)
> Total cross section: -7.772e+07 +- 2.2e+07 pb
>
> Is there something else I can try?
> Best,
> Josh
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

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