Doubts about jets in fixed-order calculations

Difficult to comment without the code.

My best guess is that you include the incoming particle (the one from the beam).
Is this possible?

Olivier

> On 1 Sep 2021, at 15:30, matteo maltoni <email address hidden> wrote:
>
> New question #698590 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/698590
>
> Dear MadGraph experts,
>
> I have some doubts about how the jets are handled during the fixed-order analysis @NLO.
>
> The process I'm considering is ( p p > l+ l- j j QCD=0 NP=2 [QCD] ); during the analysis, I put all the light QCD particles in an array pQCD(0:3,nexternal) and then I call amcatnlo_fastjetppgenkt_etamax, obtaining an array pjet(0:3,nexternal) where the jets are ordered in transverse momentum. The code I use is very similar to the one in analysis_HwU_general.f.
>
> I asked in the analysis to write down some of these arrays, and I saw that there are more than 3 non-zero entries in both pQCD and pjet, which seems weird to me because, even considering the real emission, I can't see where these extra particles and jets are coming from.
>
> Can you please help me understand what the extra entries represent, and which ones should I use to compute the quantities I need later on?
>
> Sorry if the question's trivial, I'm not so expert in fortran coding.
>
> Best,
>
> Matteo
>
> --
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> contact for MadGraph5_aMC@NLO.

Hi Olivier,

Thank you for your prompt answer.

I start the loop that fills pQCD from nincoming+1, like this:

      nQCD=0
      do j=nincoming+1,nexternal
        if(abs(ipdg(i)).le.5 .or. ipdg(i).eq.21) then
            nQCD=nQCD+1
            do i=0,3
               pQCD(i,nQCD)=p(i,j)
            enddo
        endif
      enddo

so I don't think the incoming particles are included.

This is one of the pQCD arrays I printed:

4216.4919831544157 -130.55661055556322 208.24067313187803 -4209.3224439925334 780.40657305475474 95.347471245635262 -225.59283076588065 -740.53781910392740 331.77837083452891 76.711865179268599 158.79964759025515 -281.02464130311142 426.83408345312785 -41.502725869340622 -141.44748995625253 -400.57142450225012 403.38508773197645 -79.727026266668872 -70.193240068247150 -389.14783737794261 0.0000000000000000 0.0000000000000000 0.0000000000000000 0.0000000000000000 0.0000000000000000 0.0000000000000000 0.0000000000000000 0.0000000000000000

There are 28 entries, so 7 particles, of which only 2 are null.

Best,

Matteo

Hi,

Your loop over "j"
but your condition to accept a particle use the "i" index and not the "j" one

Cheers,

Olivier

> On 1 Sep 2021, at 15:55, matteo maltoni <email address hidden> wrote:
>
> Question #698590 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/698590
>
> Status: Answered => Open
>
> matteo maltoni is still having a problem:
> Hi Olivier,
>
> Thank you for your prompt answer.
>
> I start the loop that fills pQCD from nincoming+1, like this:
>
> nQCD=0
> do j=nincoming+1,nexternal
> if(abs(ipdg(i)).le.5 .or. ipdg(i).eq.21) then
> nQCD=nQCD+1
> do i=0,3
> pQCD(i,nQCD)=p(i,j)
> enddo
> endif
> enddo
>
> so I don't think the incoming particles are included.
>
> This is one of the pQCD arrays I printed:
>
> 4216.4919831544157 -130.55661055556322 208.24067313187803
> -4209.3224439925334 780.40657305475474 95.347471245635262
> -225.59283076588065 -740.53781910392740 331.77837083452891
> 76.711865179268599 158.79964759025515 -281.02464130311142
> 426.83408345312785 -41.502725869340622 -141.44748995625253
> -400.57142450225012 403.38508773197645 -79.727026266668872
> -70.193240068247150 -389.14783737794261 0.0000000000000000
> 0.0000000000000000 0.0000000000000000 0.0000000000000000
> 0.0000000000000000 0.0000000000000000 0.0000000000000000
> 0.0000000000000000
>
> There are 28 entries, so 7 particles, of which only 2 are null.
>
> Best,
>
> Matteo
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Dear Olivier,

The typo you pointed out was indeed causing the issue; now I have at most 3 non-zero four-momenta in the pQCD and pjet arrays I printed:

1199.8950801385595 -588.34980010879769 -356.47441059494054 -976.68089199138001 268.98782917733735 151.77000852780543 105.24357726520995 -195.56100378507998 190.25738847834526 185.35352153201120 -16.066215107380252 -39.797269484295455 0.0000000000000000 0.0000000000000000 0.0000000000000000 0.0000000000000000 0.0000000000000000 0.0000000000000000 0.0000000000000000 0.0000000000000000 0.0000000000000000 0.0000000000000000 0.0000000000000000 0.0000000000000000 0.0000000000000000 0.0000000000000000 0.0000000000000000 0.0000000000000000

Thank you,

Matteo