The invariant dimuon mass from a gamma-pole is not as expected

Asked by Zirui Wang on 2017-08-25

Dear experts,

I use this card to generate h > a mu+ mu- event.

#
import model heft
# Define multiparticle labels
define p = g u c d s b u~ c~ d~ s~ b~
define j = p
define l+ = e+ mu+ ta+
define l- = e- mu- ta-
define vl = ve vm vt
define vl~ = ve~ vm~ vt~
# process
#generate g g > h > a mu+ mu-
#
output test_0825_v3
launch
# change para_card
set MH 125.0 ## Higgs mass
set WH 0.00407 ## Higgs width
# change run_card
set ebeam1 6500
set ebeam2 6500
set nevents 10000

And the mu+ mu- should come from the gamma-pole, which means the peak of the invariant mass of dimuon should be at 0.
But when I plot the dimuon mass spectrum using the output lhe file, there is no events below 4 GeV. It seems that there is a cut applied. May I know if there is any intrinsic cut in this generation process?

The mass spectrum: https://drive.google.com/open?id=0B5qg6stoWrwHMDl0RlY4LVROdVk

Best,
Zirui

Question information

Language:
English Edit question
Status:
Solved
For:
MadGraph5_aMC@NLO Edit question
Assignee:
No assignee Edit question
Solved by:
Olivier Mattelaer
Solved:
2017-08-25
Last query:
2017-08-25
Last reply:
2017-08-25

Hi,

I'm surprise that you only have a cut at 4 GeV since you should have a cut on the pt of the photon of 10 GeV according to your script.
Otherwise, they are a default --hidden-- cut related to the scale choice (the factorisation scale can not be smaller than 2GeV within the default dynamical scale)
This can be linked to your cut at 4 GeV.

Cheers,

Olivier

> On 25 Aug 2017, at 17:58, Zirui Wang <email address hidden> wrote:
>
> New question #656965 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/656965
>
> Dear experts,
>
> I use this card to generate h > a mu+ mu- event.
>
> #
> import model heft
> # Define multiparticle labels
> define p = g u c d s b u~ c~ d~ s~ b~
> define j = p
> define l+ = e+ mu+ ta+
> define l- = e- mu- ta-
> define vl = ve vm vt
> define vl~ = ve~ vm~ vt~
> # process
> #generate g g > h > a mu+ mu-
> #
> output test_0825_v3
> launch
> # change para_card
> set MH 125.0 ## Higgs mass
> set WH 0.00407 ## Higgs width
> # change run_card
> set ebeam1 6500
> set ebeam2 6500
> set nevents 10000
>
> And the mu+ mu- should come from the gamma-pole, which means the peak of the invariant mass of dimuon should be at 0.
> But when I plot the dimuon mass spectrum using the output lhe file, there is no events below 4 GeV. It seems that there is a cut applied. May I know if there is any intrinsic cut in this generation process?
>
> The mass spectrum: https://drive.google.com/open?id=0B5qg6stoWrwHMDl0RlY4LVROdVk
>
> Best,
> Zirui
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Zirui Wang (ziruiality) said : #2

Hi Olivier,

Thanks for you reply! Yes, exactly, there is a 10 GeV cut on the photon pT spectrum.
May I know if this cut can be removed? I didn't find the syntax relating to this cut.

Best,
Zirui

Hi,

You can add the line
set pta 0
To your script to remove the cut on the photon.
To remove all default cut (but not the one linked to the dynamical scale mentioned above), you can add:
set no_parton_cut
(Note that this is a quite recent command, and you need at least 2.5.5 to use it)

In order to know those syntax, the easiest it to look at the Cards/run_card.dat and you will have the list of the most common cut/parameter
(Including all of those which are not zero)

Cheers,

Olivier

> On 25 Aug 2017, at 22:03, Zirui Wang <email address hidden> wrote:
>
> Question #656965 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/656965
>
> Zirui Wang posted a new comment:
> Hi Olivier,
>
> Thanks for you reply! Yes, exactly, there is a 10 GeV cut on the photon pT spectrum.
> May I know if this cut can be removed? I didn't find the syntax relating to this cut.
>
> Best,
> Zirui
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Zirui Wang (ziruiality) said : #5

Thanks Olivier!

Best,
Zirui

Zirui Wang (ziruiality) said : #6

Thanks Olivier Mattelaer, that solved my question.