MadGraph5_aMC@NLO

The model heft cannot handle loop processes

Asked by Jia Fu Low

Hi,

I'm trying to reproduce the numbers in Table 8 (single Higgs production) of arXiv:1405.0301 . For the process "p p > h", I was able to get the LO cross section. But when I tried "p p > h [QCD]" to get the NLO cross section, I got the error "The model heft cannot handle loop processes". Am I missing something obvious?

I attach the commands I used below.

Thanks for your help,
Jia Fu

========
  (MadGraph5_aMC@NLO, version 2.3.0)

  MG5_aMC>import model heft
  INFO: Restrict model heft with file models/heft/restrict_default.dat .
  INFO: Run "set stdout_level DEBUG" before import for more information.
  INFO: Change particles name to pass to MG5 convention
  Kept definitions of multiparticles qq / l- / ss / bb / cc / j / vl / l+ / p / vl~ unchanged
  Defined multiparticle all = g u c d s u~ c~ d~ s~ a ve vm vt e- mu- ve~ vm~ vt~ e+ mu+ t b t~ b~ z w+ h h1 w- ta- ta+
  MG5_aMC>generate p p > h [QCD]
  The current model heft does not allow to generate loop corrections of type ['QCD'].
  Command "generate p p > h [QCD]" interrupted with error:
  InvalidCmd : The model heft cannot handle loop processes

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Olivier Mattelaer
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Olivier Mattelaer (olivier-mattelaer) said : 		#1

Hi,

The "heft" model that we have is indeed not NLO ready.
You need to use another model for that.

I guess that this is the model that you look for:
https://feynrules.irmp.ucl.ac.be/wiki/HiggsCharacterisation
(which allow to make some computation at NLO in the infinite top mass limit.)

In case that you want the finite top mass effect, then you need to use the "sm" model,
where g g > h [QCD] returns the loop induced processes.

Cheers,

Olivier

Revision history for this message
Jia Fu Low (jlow) said : 		#2

Hi Olivier,

Thanks a lot for the quick response! I'm interested to generate pp --> H + jets events. Being quite unfamiliar with MC generators, I thought it'd be a good exercise for me to reproduce the Table 8 numbers in the reference. Should I be using the "HiggsCharacterisation" model or the "sm" model for this purpose?

Thanks,
Jia Fu

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

Dear Jia Fu,

The number of Table 8 are indeed done with the HiggsCharacterisation model.

Cheers,

Olivier

Revision history for this message
Jia Fu Low (jlow) said : 		#4

Hi Olivier,

Thanks again! I was able to run the HiggsCharacterisation model and obtained a NLO cross section of 32.14pb (compared to 32.61pb in the table). That was pretty cool!

Thanks,
Jia Fu

Revision history for this message
Jia Fu Low (jlow) said : 		#5

Thanks Olivier Mattelaer, that solved my question.

Revision history for this message
Jia Fu Low (jlow) said : 		#6

Hi Olivier,

I'm sorry to bug you still. For the "p p > h" process, I got the correct NLO cross section; however, for the "p p > h j", I got almost double: 32.30pb (vs 14.22pb in the table). The commands I used are:

MG5_aMC>import model HC_NLO_X0_UFO-heft
MG5_aMC>generate p p > x0 /t [QCD] @0
MG5_aMC>add process p p > x0 j / t [QCD] @1

What am I missing?

Thanks,
Jia Fu

Revision history for this message
Olivier Mattelaer (olivier-mattelaer) said : 		#7

Hi,

> MG5_aMC>import model HC_NLO_X0_UFO-heft
> MG5_aMC>generate p p > x0 /t [QCD] @0
> MG5_aMC>add process p p > x0 j / t [QCD] @1

So this is 0+1j (not only 1j) so this is not reported in the table and has some double counting if you did not use some merging like FxFx.

Cheers,

Olivier

On 05 Aug 2015, at 02:16, Jia Fu Low <email address hidden> wrote:

> Question #269991 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/269991
>
> Jia Fu Low posted a new comment:
> Hi Olivier,
>
> I'm sorry to bug you still. For the "p p > h" process, I got the correct
> NLO cross section; however, for the "p p > h j", I got almost double:
> 32.30pb (vs 14.22pb in the table). The commands I used are:
>
> MG5_aMC>import model HC_NLO_X0_UFO-heft
> MG5_aMC>generate p p > x0 /t [QCD] @0
> MG5_aMC>add process p p > x0 j / t [QCD] @1
>
> What am I missing?
>
> Thanks,
> Jia Fu
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Revision history for this message
Jia Fu Low (jlow) said : 		#8

Hi Olivier,

Thanks again for your reply. So I followed http://amcatnlo.web.cern.ch/amcatnlo/FxFx_merging.htm , doing fixed_order=ON, the cross section is slightly reduced, but not by much (now 29.4 pb). I did also fixed_order=OFF, using Herwig6 for parton shower, and I got almost the same cross section. So I guess I need to follow through with an analysis script to count the number of events for each exclusive jet bins (0j, 1j, etc) in order to figure out the cross sections. Does that sound about right?

Thanks for your help,
Jia Fu

Revision history for this message
Olivier Mattelaer (olivier-mattelaer) said : 		#9

Hi,

If you want to reproduce the number of the paper, this is clearly not necessary.
You just have to generate the 1j without generating the 0j. and check that the cut that you use are those that we use in the paper.

Cheers,

Olivier

On 05 Aug 2015, at 17:51, Jia Fu Low <email address hidden> wrote:

> Question #269991 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/269991
>
> Jia Fu Low posted a new comment:
> Hi Olivier,
>
> Thanks again for your reply. So I followed
> http://amcatnlo.web.cern.ch/amcatnlo/FxFx_merging.htm , doing
> fixed_order=ON, the cross section is slightly reduced, but not by much
> (now 29.4 pb). I did also fixed_order=OFF, using Herwig6 for parton
> shower, and I got almost the same cross section. So I guess I need to
> follow through with an analysis script to count the number of events for
> each exclusive jet bins (0j, 1j, etc) in order to figure out the cross
> sections. Does that sound about right?
>
> Thanks for your help,
> Jia Fu
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Revision history for this message
Jia Fu Low (jlow) said : 		#10

Hi Olivier,

You are right, that's what I was missing. Now I get 15.50 pb, consistent with 14.22 pb in the paper. Thank you very much for your help!

Best regards,
Jia Fu