# Making an invariant mass cut

Asked by Ameir Shaa on 2018-01-21

How do I make an invariant mass cut (of say 2GeV) in MG5 for a simple drell-yan process such as p p > mm+ mm-? mm is a custom defined particle with custom couplings to the photon and Z boson.

I notice the options in the run card as follows:

#*********************************************************************
# Minimum and maximum invariant mass for pairs *
# WARNING: for four lepton final state mmll cut require to have *
# different lepton masses for each flavor! *
#*********************************************************************
0.0 = mmjj ! min invariant mass of a jet pair
0.0 = mmbb ! min invariant mass of a b pair
0.0 = mmaa ! min invariant mass of gamma gamma pair
0.0 = mmll ! min invariant mass of l+l- (same flavour) lepton pair
-1.0 = mmjjmax ! max invariant mass of a jet pair
-1.0 = mmbbmax ! max invariant mass of a b pair
-1.0 = mmaamax ! max invariant mass of gamma gamma pair
-1.0 = mmllmax ! max invariant mass of l+l- (same flavour) lepton pair
{} = mxx_min_pdg ! min invariant mass of a pair of particles X/X~ (e.g. {6:250})
{'default': False} = mxx_only_part_antipart ! if True the invariant mass is applied only
! to pairs of particle/antiparticle and not to pairs of the same pdg codes.
#*********************************************************************
# Minimum and maximum invariant mass for all letpons *
#*********************************************************************
0.0 = mmnl ! min invariant mass for all letpons (l+- and vl)
-1.0 = mmnlmax ! max invariant mass for all letpons (l+- and vl)
#*********************************************************************

Which of these would I have to edit to produce the desired invariant mass cut?

Many thanks,

Ameir

## Question information

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Solved by:
Olivier Mattelaer
Solved:
2018-01-23
Last query:
2018-01-23
2018-01-21
 Olivier Mattelaer (olivier-mattelaer) said on 2018-01-21: #1

Hi,

One think that you need to be careful about is the implicit cut associate to the factorisation scale.
If that scale is below 4GeV^2 you have an automatic cut of the phase-space point.

Then concerning your question, the use of mxx_min_pdg is the appropriate cut in your case.
What is the PDG code of your particle? Assuming that it is 123456
then you should put
{123456: 2} = mxx_min_pdg
For your process, the value of mxx_only_part_antipart is irrelevant.

Cheers,

Olivier

> On 21 Jan 2018, at 13:17, Ameir Shaa <email address hidden> wrote:
>
> New question #663363 on MadGraph5_aMC@NLO:
>
>
> How do I make an invariant mass cut (of say 2GeV) in MG5 for a simple drell-yan process such as p p > mm+ mm-? mm is a custom defined particle with custom couplings to the photon and Z boson.
>
> I notice the options in the run card as follows:
>
> #*********************************************************************
> # Minimum and maximum invariant mass for pairs *
> # WARNING: for four lepton final state mmll cut require to have *
> # different lepton masses for each flavor! *
> #*********************************************************************
> 0.0 = mmjj ! min invariant mass of a jet pair
> 0.0 = mmbb ! min invariant mass of a b pair
> 0.0 = mmaa ! min invariant mass of gamma gamma pair
> 0.0 = mmll ! min invariant mass of l+l- (same flavour) lepton pair
> -1.0 = mmjjmax ! max invariant mass of a jet pair
> -1.0 = mmbbmax ! max invariant mass of a b pair
> -1.0 = mmaamax ! max invariant mass of gamma gamma pair
> -1.0 = mmllmax ! max invariant mass of l+l- (same flavour) lepton pair
> {} = mxx_min_pdg ! min invariant mass of a pair of particles X/X~ (e.g. {6:250})
> {'default': False} = mxx_only_part_antipart ! if True the invariant mass is applied only
> ! to pairs of particle/antiparticle and not to pairs of the same pdg codes.
> #*********************************************************************
> # Minimum and maximum invariant mass for all letpons *
> #*********************************************************************
> 0.0 = mmnl ! min invariant mass for all letpons (l+- and vl)
> -1.0 = mmnlmax ! max invariant mass for all letpons (l+- and vl)
> #*********************************************************************
>
> Which of these would I have to edit to produce the desired invariant mass cut?
>
>
> Many thanks,
>
> Ameir
>
> --

 Ameir Shaa (ameirshaa) said on 2018-01-21: #2

Hi Olivier,

I just need a clarification. Why do you say that the value of mxx_only_part_antipart is irrelevant?

Many thanks,

Ameir

 Olivier Mattelaer (olivier-mattelaer) said on 2018-01-21: #3

so setting mxx_only_part_antipart on True or False will not change anything.

This switch is more for case where you have two particle and two anti-particle. If you put it on True then you do not constaint the invariant mass between the two particle (same between the two anti-particle).
But you do so if you put it on False.
To be complete, this entry is a dictionary so you have the choice to put it on True/False for each pdg independently.

Cheers,

Olivier

> On 21 Jan 2018, at 18:22, Ameir Shaa <email address hidden> wrote:
>
> Question #663363 on MadGraph5_aMC@NLO changed:
>
>
> Ameir Shaa is still having a problem:
> Hi Olivier,
>
>
> I just need a clarification. Why do you say that the value of
> mxx_only_part_antipart is irrelevant?
>
> Many thanks,
>
> Ameir
>
> --