Zero cross section in Madgraph Version 2.4.2

Hi,

Like this I do not remember any change that are trivially related to such effect.
Now they are so many stuff that change the last 3 years that it is difficult to remember all the issue that I have fixed (in top of knowing if the fix where discover in a development code or in a released code). In top of that CMS never use an official version of the code but apply a bunch of patch (so your version is likely closer to 2.5.0 than it is of 2.4.2) which make this impossible to debug on our side.

Finally what kind of "tweak" do you expect? if you want a patch, I can create you a patch to move from 2.4.2 to 2.6.6 that will solve your issue. But I guess that you are not allowed to use patch.

Cheers,

Olivier

> On 19 Sep 2019, at 01:08, Andrea Delgado <email address hidden> wrote:
>
> New question #684024 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/684024
>
> Hello all,
>
> Thank you for your help in advance.
>
> I am trying to run Madgraph importing a model for a Z' with 4 coupling parameters.
>
> I do:
> import model zprime_UFO
> define p = p b b~
> define j = j b b~
> generate p p > zp, zp > j j@0
> add process p p > zp j, zp > j j@1
> add process p p > zp j j, zp > j j@2
> output zprime_dbs1test
>
> I am trying to run Madgraph 2.4.2 because this is the required version for 2016 CMS analyses, however, whenever I set one of my parameters to 1.0 I get a 0 cross section. If I run the exact same setup on the latest version you can download from the website, I get a cross section !=0, which is what I expect from the model.
>
> Do you have any insight as to what might have changed between releases that can cause this difference? Or how can I tweak version 2.4.2 to work with this model and phase space?
>
> Thanks again
>
>
>
>
> --
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> contact for MadGraph5_aMC@NLO.

In MadGraph Version 2.4.2, the concept of "zero cross section" typically refers to a situation where the calculated cross section for a particular process or interaction is found to be exactly zero. This can occur for various reasons, such as kinematic constraints that prevent the process from occurring at the given energy or momentum configurations, conservation laws, or mathematical simplifications. It's essential to investigate the physics behind a zero cross section carefully, as it might indicate a physically impossible process or a limitation in the chosen model or configuration. Researchers often use such information to refine their theoretical framework or experimental setups to better understand and predict particle interactions. https://chatgptlogin.club/

Ensure that the process you are trying to simulate is defined correctly. A mistake in the process definition can lead to a situation where no physical process matches your definition, resulting in a zero cross section.

Parameter Settings: Check the model parameters and make sure they are set correctly. Parameters that are outside of physical ranges or incorrectly set can lead to a zero cross section.
https://iecsconsultant.com/
Phase Space Cuts: If you have applied phase space cuts, they might be too stringent, effectively eliminating all possible events. Review and adjust the cuts if necessary.

Model Files: There might be an issue with the model files you are using. Ensure that they are correctly implemented and compatible with MadGraph 2.4.2.

Version Specific Issues: There could be bugs or issues specific to MadGraph 2.4.2. Check the MadGraph forum or user groups for any known issues with this version.

Luminosity and Energy Settings: Incorrect settings for the collider luminosity or energy can also result in a zero cross section. Make sure these are set appropriately for your simulation.