MadGraph5_aMC@NLO

Consistently implement a simple SSM Z' model

Asked by Sebastian Yan

Hello Madgraph experts,

I am writing to see what would be the proper procedure to implement a simple SSM Z' boson in Madgraph.

The original idea is to keep the couplings the same as the SM but alternate the vev to change the mass of the Z boson. However, in Madgraph the Z mass is set to be an external parameter.

In this case, I am wondering if it would be safe to change the Z mass directly. Or other parameters are also needed to be modified accordingly to keep the model consistent?

Thanks a lot!

Question information

Language:
English Edit question
Status:
Answered
For:
MadGraph5_aMC@NLO Edit question
Assignee:
No assignee Edit question
Last query:
Last reply:
Revision history for this message
Olivier Mattelaer (olivier-mattelaer) said : 		#1

Hi,

When you change the Z mass within the model other parameter (like the W mass) will be automatically changed.
So I do not see any issue to change the Z mass.

Cheers,

Olivier

Revision history for this message
Sebastian Yan (sebyan190) said : 		#2

Hello Olivier,

Thanks for your prompt reply!

I have a few further questions, however:

1. By setting the Z mass along, I got the xsec for "generate p p > z" is 348pb. However, the xsec for "generate p p > z, z > j j" is 2.9e6 pb, which is unreasonable.

I noticed that I got an error with the second command: WARNING: Failed to update dependent parameter. This might create trouble for external program (like MadSpin/shower/...)

I think there might be some inconsistencies within the model parameters.

What do you think?

Thanks a lot!

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

The inconsistency is related to the width of the Z which is an external input for MG5aMC.
If you change the mass of the Z you have to change the width of the Z consistently in order to get physical result for processes where the particle can be onshell and then decay.

Cheers,

Olivier

Can you help with this problem?

Provide an answer of your own, or ask Sebastian Yan for more information if necessary.

To post a message you must log in.