MadGraph5_aMC@NLO

Process gg > h: few questions

Asked by Maksym Ovchynnikov

Hu!

I am trying to generate a process of production of the Higgs boson in pp collisions. I have few questions:

1) Does the model hgg_plugin allows me to calculate this cross-section (assuming that the gluon fusion gives the main contribution into the total Higgs production cross-section)? If yes, is the syntax for the process g g > h? If yes, how does it take into account that initial gluon pair is inside two colliding protons?

2) I tried to generate process g g > h after importing hgg_plugin. generate process goes well, but when trying to output I have got an error:

"...write debug file MG5_debug
If you need help with this issue please contact us on https://answers.launchpad.net/mg5amcnlo
MadGraph5Error : Unable to evaluate mdl_MW = cmath.sqrt(mdl_MZ__exp__2/2. + cmath.sqrt(mdl_MZ__exp__4/4. - (mdl_aEW*cmath.pi*mdl_MZ__exp__2)/(mdl_Gf*mdl_sqrt__2))): raise error: name 'mdl_aEW' is not defined..."

What is a reason for this error and how to fix it?

3) I tried to generate a process p p > h in Higgs_Effective_Couplings_UFO, but when launching it I obtained

"Error detected in "generate_events run_01"
write debug file /home/movchynnikov/Dropbox/MG5/bin/higgs_lhc/run_01_tag_1_debug.log
If you need help with this issue please contact us on https://answers.launchpad.net/mg5amcnlo
MadGraph5Error : A compilation Error occurs when trying to compile /home/movchynnikov/Dropbox/MG5/bin/higgs_lhc/SubProcesses/P1_gg_h.
 The compilation fails with the following output message:
     gfortran -O -w -fbounds-check -fPIC -ffixed-line-length-132 -w -c driver.f -I../../Source/
     gfortran -O -w -fbounds-check -fPIC -ffixed-line-length-132 -w -c myamp.f -I../../Source/
     gfortran -O -w -fbounds-check -fPIC -ffixed-line-length-132 -w -c genps.f -I../../Source/
     gfortran -O -w -fbounds-check -fPIC -ffixed-line-length-132 -w -c unwgt.f -I../../Source/
     genps.f:328:25:

           & nbranch,P,M,S,X,jac,pswgt)
                              1
     Error: Actual argument contains too few elements for dummy argument ‘x’ (12/40) at (1)
     genps.f:60:53:

            call gen_mom(iconfig,mincfig,maxcfig,invar,wgt,x,p)
                                                          1
     Error: Actual argument contains too few elements for dummy argument ‘x’ (2/12) at (1)
     make: *** [makefile:60: genps.o] Error 1
     make: *** Waiting for unfinished jobs....

 Please try to fix this compilations issue and retry.
 Help might be found at https://answers.launchpad.net/mg5amcnlo.
 If you think that this is a bug, you can report this at https://bugs.launchpad.net/mg5amcnlo..."

Whan can be a reason here?

Thank you for your help.

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Olivier Mattelaer
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Revision history for this message
Olivier Mattelaer (olivier-mattelaer) said : 		#1

Hi,

1) yes. the cross-section reported is the convolution of the amplitude square times the Parton-distribution function.
The default PDF is NNPDF2.3 but you can change that in the run_card.dat
Note that such cross-section is LO accurate and does not take into account the effect of the b-mass and lighter quark (which means that you over-estimate the LO cross-section) The cross-section need anyway to be rescaled to N^3LO and the associated K-factor is actually much bigger than one.

2) I guess that you are using an old version of MG5, since I remember that issue but it is fixed by now.
I actually do not know the model: Higgs_Effective_Couplings_UFO, I would rather haved used the heft model which is for sure the exact equivalent of the hgg_plugin

3) Your error with "Higgs_Effective_Couplings_UFO" is a ggc version 8 incompatibility with old version of MG5aMC. (never use recent compiler on old code this typically does not work). So here you can either use gcc7 instead of gcc8 or update to the latest version of MG5.

Cheers,

Olivier

Revision history for this message
Maksym Ovchynnikov (name-xxx) said : 		#2

Dear Olivier, should I expect that the cross section obtained by hgg_plugin be 2-3 times smaller than the real cross section?
And what about longitudinal momenta distribution? Should I expect that it is more or less correct? Or NLO corrections will change it significantly?

Revision history for this message
Olivier Mattelaer (olivier-mattelaer) said : 		#3

Hi,

Dear Olivier, should I expect that the cross section obtained by hgg_plugin be 2-3 times smaller than the real cross section?

Yes this sounds what I expect.

And what about longitudinal momenta distribution? Should I expect that it is more or less correct? Or NLO corrections will change it significantly?

Do not know for sure. I think it should not be too bad (but you are likely to have huge theoretical uncertainty with such method of computation. If you want a rough estimate this can be ok, but if you want to be a bit precise. You should either do a matched/merged generation like it is done in rXiv:1507.00020 (with full loop-computation) or do the same at NLO accuracy but with approximation to include the finite mass of the top.
like in arXiv:1401.7340<http://arXiv.org/abs/arXiv:1401.7340>

Cheers,

Olivier

On 17 Apr 2019, at 19:08, Maksym Ovchynnikov <<email address hidden><mailto:<email address hidden>>> wrote:

Question #680306 on MadGraph5_aMC@NLO changed:
https://answers.launchpad.net/mg5amcnlo/+question/680306

   Status: Answered => Open

Maksym Ovchynnikov is still having a problem:
Dear Olivier, should I expect that the cross section obtained by hgg_plugin be 2-3 times smaller than the real cross section?
And what about longitudinal momenta distribution? Should I expect that it is more or less correct? Or NLO corrections will change it significantly?

--
You received this question notification because you are an answer
contact for MadGraph5_aMC@NLO.

Revision history for this message
Olivier Mattelaer (olivier-mattelaer) said : 		#4

I forget to mention this paper:
arXiv:1607.00763<http://arXiv.org/abs/arXiv:1607.00763>

Which explains how to do the re-weighitng to include the top mass effect within MG5aMC

Cheers,

Olivier

On 17 Apr 2019, at 20:31, Olivier Mattelaer <<email address hidden><mailto:<email address hidden>>> wrote:

Hi,

Dear Olivier, should I expect that the cross section obtained by hgg_plugin be 2-3 times smaller than the real cross section?

Yes this sounds what I expect.

And what about longitudinal momenta distribution? Should I expect that it is more or less correct? Or NLO corrections will change it significantly?

Do not know for sure. I think it should not be too bad (but you are likely to have huge theoretical uncertainty with such method of computation. If you want a rough estimate this can be ok, but if you want to be a bit precise. You should either do a matched/merged generation like it is done in rXiv:1507.00020 (with full loop-computation) or do the same at NLO accuracy but with approximation to include the finite mass of the top.
like in arXiv:1401.7340<http://arxiv.org/abs/arXiv:1401.7340>

Cheers,

Olivier

On 17 Apr 2019, at 19:08, Maksym Ovchynnikov <<email address hidden><mailto:<email address hidden>>> wrote:

Question #680306 on MadGraph5_aMC@NLO changed:
https://answers.launchpad.net/mg5amcnlo/+question/680306

   Status: Answered => Open

Maksym Ovchynnikov is still having a problem:
Dear Olivier, should I expect that the cross section obtained by hgg_plugin be 2-3 times smaller than the real cross section?
And what about longitudinal momenta distribution? Should I expect that it is more or less correct? Or NLO corrections will change it significantly?

--
You received this question notification because you are an answer
contact for MadGraph5_aMC@NLO.

Revision history for this message
Maksym Ovchynnikov (name-xxx) said : 		#5

Dear Olivier,

thank you very much! One last question: by heft you mean this model, https://cp3.irmp.ucl.ac.be/projects/madgraph/wiki/Models/HiggsEffective ?

Revision history for this message
Best Olivier Mattelaer (olivier-mattelaer) said : 		#6

yes that's the theory description of the model.

to get it you can just type "import model heft" obviously

Cheers,

Olivier

> On 17 Apr 2019, at 23:12, Maksym Ovchynnikov <email address hidden> wrote:
>
> Question #680306 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/680306
>
> Status: Answered => Open
>
> Maksym Ovchynnikov is still having a problem:
> Dear Olivier,
>
> thank you very much! One last question: by heft you mean this model,
> https://cp3.irmp.ucl.ac.be/projects/madgraph/wiki/Models/HiggsEffective
> ?
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Revision history for this message
Maksym Ovchynnikov (name-xxx) said : 		#7

Thanks Olivier Mattelaer, that solved my question.