check that you do not have -integrable- singularity in your amplitude.

What is the value of the width for vlm?
If set to zero, then the cross-section is indeed infinite and it is impossible to integrate it numerically.
One easy test is to do
generate mu+ mu- > vlm- vlm+
which is (unlikely) independent of the width of the vlm particle and check that the result is finite.

Cheers,

olivier

> On 4 Jan 2024, at 13:25, Feyza Baspehlivan <email address hidden> wrote:
>
> New question #708901 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/708901
>
> Hello,
>
> We are implementing a new model that includes SM. Our model defines 3 new heavy charged and neutral lepton couples. We also added the right-handed neutrino to the SM. In FeynRules we implemented these particles and their interaction Lagrangians as an addendum to the SM particles and Lagrangians. When we run this model in MadGraph for a particular production and decay process for muon collider at 6 TeV center of mass energy, we got this issue and a very absurd cross-section:
>
>
> ...
>
> INFO: fail to reach target 1000
> failed to generate enough events. Please follow one of the following suggestions to fix the issue:
> - set in the run_card.dat 'sde_strategy' to 2
> - set in the run_card.dat 'hard_survey' to 1 or 2.
> - reduce the number of requested events (if set too high)
> - check that you do not have -integrable- singularity in your amplitude.
> === Results Summary for run: run_02 tag: tag_1 ===
>
> Cross-section : 1.174e+15 +- 5.825e+14 pb
> Nb of events : 1
>
> ...
>
>
> The process is : generate mu+ mu- > vlm- vlm+ , vlm+ > z mu+ , vlm- > z mu-
>
> We tried to fix it by changing 'sde_strategy' to 2 but did not work at all. After we changed it, it says 'sde_strategy' to 1, appearing with the same error. Also, the second option gave the same ('hard_survey').
>
> I have no idea how to fix this issue especially if it results from a singularity in amplitude.
>
> Additionally, just to check, when we run the process: generate e+ e- > vle- vle+ , vle+ > z e+ , vle- > z e- , cross-section and number of events values at reasonable values. What would be the solution for the muon-antimuon process?
>
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Cross-section of mu+ mu- > vlm- vlm+ process is a finite number: 3.2 fb. How can I find out what value is given to the width of the vlm?

This might depend of your model, but it should be set in the param_card.dat.
If you do not know which value to use you can set it to auto such that MG5aMC does compute the tree-level width for that particle.

Cheers,

Olivier

Hello Olivier,

Thank you for your response. I set the width of vlm as AUTO or 1.0 GeV and I got the same result:

...

INFO: Combining Events
INFO: fail to reach target 10000
failed to generate enough events. Please follow one of the following suggestions to fix the issue:
  - set in the run_card.dat 'sde_strategy' to 1
  - set in the run_card.dat 'hard_survey' to 1 or 2.
  - reduce the number of requested events (if set too high)
  - check that you do not have -integrable- singularity in your amplitude.
  === Results Summary for run: run_01 tag: tag_1 ===

     Cross-section : 6.273e+11 +- 1.369e+12 pb
     Nb of events : 21

store_events
INFO: Storing parton level results
INFO: End Parton
reweight -from_cards
decay_events -from_cards
INFO: storing files of previous run
INFO: Done
quit
INFO:
more information in /home/feyza/width/index.html

...

Is there any other possibility for the problem or did I make something wrong?

Maybe the width is hardcoded to zero at the model level?
Can you check that the UFO model does allow to have a non zero width for that particle?

Cheers,

Olivier

Hello again,

Thank you for your helpful response again. I checked the UFO file, and as you said width of the vlm particle (DVlm) was set to param.ZERO. I changed it to param.DVlm, as we implemented decay formulas to the .fr file. So, decay widths are calculated according to the formulas we have given. I checked all terms have a value in the decay width formula in parameters.py. Sadly, this time MadGraph gave another error before card modifications:

...

The following switches determine which programs are run:
/===========================================================================\
| 1. Choose the shower/hadronization program shower = OFF |
| 2. Choose the detector simulation program detector = OFF |
| 3. Choose an analysis package (plot/convert) analysis = OFF |
| 4. Decay onshell particles madspin = OFF |
| 5. Add weights to events for new hypp. reweight = OFF |
\===========================================================================/
Either type the switch number (1 to 5) to change its setting,
Set any switch explicitly (e.g. type 'shower=Pythia8' at the prompt)
Type 'help' for the list of all valid option
Type '0', 'auto', 'done' or just press enter when you are done.
>
ERROR: Current param_card is not valid. We are going to use the default one.
ERROR: problem detected: mass (9000009,) is already define to 1000.0 impossible to assign 0.06510876
Command "generate_events run_01" interrupted with error:
InvalidParamCard : mass (9000009,) is already define to 1000.0 impossible to assign 0.06510876
Please report this bug on https://bugs.launchpad.net/mg5amcnlo
More information is found in 'ME5_debug'.
Please attach this file to your report.
INFO:
quit
INFO:

.....

And automatically changed width of vlm to 0 in the param.card. Somehow, as I understand, it seems to think that we are trying to assign width to mass. What can be the reason behind this?

Thanks Olivier Mattelaer, that solved my question.