Gluon color singlet state produced in some processes

Asked by Joshua Lin on 2018-06-01

 When generating an event with madgraph like this:

generate c~ g > H g c~ QED=1 [QCD]
launch

if I look into the LHE event card, I get events such as the following:

  <event>
    5 0 +4.0285366e-02 1.36540700e+02 7.54677100e-03 1.21806100e-01
          -4 -1 0 0 0 501 +0.0000000000e+00 +0.0000000000e+00 +2.9419141131e+03 2.9419141131e+03 0.0000000000e+00 0.0000e+00 -1.0000e+00
          21 -1 0 0 501 502 -0.0000000000e+00 -0.0000000000e+00 -2.1835375839e+01 2.1835375839e+01 0.0000000000e+00 0.0000e+00 -1.0000e+00
          25 1 1 2 0 0 +4.5770992300e+01 +2.9989942130e+01 +2.0255992823e+02 2.4423330013e+02 1.2500000000e+02 0.0000e+00 0.0000e+00
          21 1 1 2 501 501 -1.3125965953e+01 +2.3701158420e+01 +3.1121389496e+02 3.1239097987e+02 0.0000000000e+00 0.0000e+00 -1.0000e+00
          -4 1 1 2 0 502 -3.2645026347e+01 -5.3691100550e+01 +2.4063049140e+03 2.4071252089e+03 0.0000000000e+00 0.0000e+00 -1.0000e+00
   <mgrwt>
   <rscale> 4 0.13654070E+03</rscale>
   <asrwt>0</asrwt>
   <pdfrwt beam="1"> 1 -4 0.45260186E+00 0.13654070E+03</pdfrwt>
   <pdfrwt beam="2"> 1 21 0.33592909E-02 0.13654070E+03</pdfrwt>
   <totfact> 0.87394861E+01</totfact>
   </mgrwt>
   </event>

where a gluon singlet state has been produced (with color tags 501 501). Is this expected behaviour? It seems when I try to subsequently shower the event with Pythia, it gives me the error 'unphysical color flow'

Question information

Language:
English Edit question
Status:
Answered
For:
MadGraph5_aMC@NLO Edit question
Assignee:
Valentin Hirschi Edit question
Last query:
2018-06-01
Last reply:
2018-06-07

Hi,

Thanks for reporting this.

Looks like the development version has the full loop-induced crashing for the moment.
So i would need to fix that first. I expect to look into your problem on thursday.

Now can you send me the content of the file
SubProcesses/P0_qg_hgq/leshouches.inc

in my case I have:
> DATA (IDUP(I,1,1),I=1,5)/-4,21,25,21,-4/
> DATA (MOTHUP(1,I),I=1, 5)/ 0, 0, 1, 1, 1/
> DATA (MOTHUP(2,I),I=1, 5)/ 0, 0, 2, 2, 2/
> DATA (ICOLUP(1,I,1,1),I=1, 5)/ 0,503, 0,503, 0/
> DATA (ICOLUP(2,I,1,1),I=1, 5)/501,502, 0,502,501/
> DATA (ICOLUP(1,I,2,1),I=1, 5)/ 0,501, 0,503, 0/
> DATA (ICOLUP(2,I,2,1),I=1, 5)/501,502, 0,502,503/
> DATA (ICOLUP(1,I,3,1),I=1, 5)/ 0,503, 0,503, 0/
> DATA (ICOLUP(2,I,3,1),I=1, 5)/501,502, 0,501,502/

In my case it sounds reasonable since no colour structure correspond to your events.
(meaning that the error is at the time of writing the events). If you do not have the same file,
then I would probably need to assign someone else on this bug report.

Cheers,

Olivier

> On 2 Jun 2018, at 00:46, Joshua Lin <email address hidden> wrote:
>
> New question #669851 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/669851
>
> When generating an event with madgraph like this:
>
> generate c~ g > H g c~ QED=1 [QCD]
> launch
>
> if I look into the LHE event card, I get events such as the following:
>
> <event>
> 5 0 +4.0285366e-02 1.36540700e+02 7.54677100e-03 1.21806100e-01
> -4 -1 0 0 0 501 +0.0000000000e+00 +0.0000000000e+00 +2.9419141131e+03 2.9419141131e+03 0.0000000000e+00 0.0000e+00 -1.0000e+00
> 21 -1 0 0 501 502 -0.0000000000e+00 -0.0000000000e+00 -2.1835375839e+01 2.1835375839e+01 0.0000000000e+00 0.0000e+00 -1.0000e+00
> 25 1 1 2 0 0 +4.5770992300e+01 +2.9989942130e+01 +2.0255992823e+02 2.4423330013e+02 1.2500000000e+02 0.0000e+00 0.0000e+00
> 21 1 1 2 501 501 -1.3125965953e+01 +2.3701158420e+01 +3.1121389496e+02 3.1239097987e+02 0.0000000000e+00 0.0000e+00 -1.0000e+00
> -4 1 1 2 0 502 -3.2645026347e+01 -5.3691100550e+01 +2.4063049140e+03 2.4071252089e+03 0.0000000000e+00 0.0000e+00 -1.0000e+00
> <mgrwt>
> <rscale> 4 0.13654070E+03</rscale>
> <asrwt>0</asrwt>
> <pdfrwt beam="1"> 1 -4 0.45260186E+00 0.13654070E+03</pdfrwt>
> <pdfrwt beam="2"> 1 21 0.33592909E-02 0.13654070E+03</pdfrwt>
> <totfact> 0.87394861E+01</totfact>
> </mgrwt>
> </event>
>
> where a gluon singlet state has been produced (with color tags 501 501). Is this expected behaviour? It seems when I try to subsequently shower the event with Pythia, it gives me the error 'unphysical color flow'
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Hi,

Just to comment that the problem for loop-induced in the development version is fixed.
I'm running your process on my laptop to have those ready for thursday.

Cheers,

Olivier

Joshua Lin (joshuazlin) said : #3

Hi,

The contents of my SubProcesses/P0_qg_hgq/leshouches.inc file are as follows:

        DATA (IDUP(I,1,1),I=1,5)/-4,21,25,21,-4/
        DATA (MOTHUP(1,I),I=1, 5)/ 0, 0, 1, 1, 1/
        DATA (MOTHUP(2,I),I=1, 5)/ 0, 0, 2, 2, 2/
        DATA (ICOLUP(1,I,1,1),I=1, 5)/ 0,503, 0,503, 0/
        DATA (ICOLUP(2,I,1,1),I=1, 5)/501,502, 0,502,501/
        DATA (ICOLUP(1,I,2,1),I=1, 5)/ 0,501, 0,503, 0/
        DATA (ICOLUP(2,I,2,1),I=1, 5)/501,502, 0,502,503/
        DATA (ICOLUP(1,I,3,1),I=1, 5)/ 0,503, 0,503, 0/
        DATA (ICOLUP(2,I,3,1),I=1, 5)/501,502, 0,501,502/

which looks the same as what you have posted above

Cheers, Josh

Hi Joshua,

I will need to assign this to Valentin since this seems to be related to his area of exptertise.

One temporary/hacky solution is to change the file
SubProcesses/P0_qg_hgq/coloramps.inc
and change the line:
DATA(ICOLAMP(I,7,1),I=1,3)/.FALSE.,.TRUE.,.TRUE./
to
DATA(ICOLAMP(I,7,1),I=1,3)/.FALSE.,.TRUE.,.FALSE./

Cheers,

Olivier.

Hi Valentin,

The problem seems to be related to a wrong assignment of the LC diagram in case of loop-induced processes.
In this case the following diagram (G7)

ggggggggXhhhhhhhhhh
                    g
                    g ----------------------
  --------------X-----------------------X
                                                     ggggggggggggg

 C Diagram 7
      DATA MAPCONFIG(7)/7/
      DATA (IFOREST(I,-1,7),I=1,2)/5,4/
      DATA (SPROP(I,-1,7),I=1,1)/-4/
      DATA TPRID(-1,7)/0/
      DATA (IFOREST(I,-2,7),I=1,2)/1,-1/
      DATA TPRID(-2,7)/21/
      DATA (SPROP(I,-2,7),I=1,1)/0/
      DATA (IFOREST(I,-3,7),I=1,2)/-2,3/

Has two color which are consider LC:
      DATA(ICOLAMP(I,7,1),I=1,3)/.FALSE.,.TRUE.,.TRUE./
While the second one does not make sense to be tagged as LC.
( you can see the three color-flow in the above post)

We can discuss on skype if something is not clear and/or if you need my help.

Cheers,

Olivier

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