Problem in neutralino decays to gravitino

Asked by Juhi Dutta on 2018-11-19

Dear experts,

I am using the goldstino-gravitino UFO from Feynrules in Madgraph5 to generate the following process:

generate p p > n1 x1+ ,n1 > z grv
add process p p > n1 x1+ @2
output check_n1cha1

I obtain the following results after parton level run.

Net cross-section = 0.000342 GeV
For p p > n1 x1+ ,n1 > z grv , cross-section = 5.961*10^-13 GeV
For p p > n1 x1+ @2, cross-section = 0.0003375

The decay width of the lightest neutralino n1 is 3.47181007E-13 and the branching fraction to z grv is 0.548. Hence I was expecting a final cross-section value for the process involving decay of the neutralino to be production cross-section X branching ratio.
Hence I expect a value of 0.0003375*0.548 = 0.00018495. However the result I obtain is 5.961*10^-13 GeV.

This huge suppression is occuring whenever the neutralino decays to the gravitino. Also, the neutralino width gets reset to 0.0 for consistency during the run. I do not encounter this for other processes where the decays to gravitino don't enter. Could you kindly let me know what I should do to resolve this matter?

With Best Regard

Juhi

Question information

Language:
English Edit question
Status:
Answered
For:
MadGraph5_aMC@NLO Edit question
Assignee:
No assignee Edit question
Last query:
2018-11-21
Last reply:
2018-11-21

Olivier Mattelaer suggests this article as an answer to your question:
FAQ #2442: “why production and decay cross-section didn't agree.”.

Did you read the above FAQ?

If this does not help you. Do not hesitate to re-open this question.

Cheers,

Olivier

Juhi Dutta (dutta-juhi91) said : #3

Hi,

Thank you for the above link. Sorry for the trouble but I realised that the default width for n1 was set to width.ZERO and not the external parameter in particles.py which led to the warning for the decay width being set to 0. This removes the warning for n1. but there is another warning for n2:

WARNING: For consistency, the width of particle 1000023 (n2) is changed to -9.643513e-11.
The mass of n2 is -916.0 GeV. Could you please suggest how to resolve this issue?

Best Regards,

Juhi

Did you use 2.6.4?

This should be solve in that version in principle.

Cheers,

Olivier

Juhi Dutta (dutta-juhi91) said : #5

Hi,

I was earlier using version 2.6.2. I checked using v2.6.4, here the following warnings were displayed:

WARNING: Particle 1000022 will use a fake width ( 0.0009153118 instead of 3.47181007e-13 ).
Cross-section will be rescaled according to NWA if needed.To force exact treatment reduce the value of 'small_width_treatment' parameter of the run_card
WARNING: Particle 1000023 will use a fake width ( -0.000917832 instead of 9.643513e-11 ).
Cross-section will be rescaled according to NWA if needed.To force exact treatment reduce the value of 'small_width_treatment' parameter of the run_card
WARNING: Particle 1000024 will use a fake width ( 0.000916197 instead of 7.102998e-13 ).
Cross-section will be rescaled according to NWA if needed.To force exact treatment reduce the value of 'small_width_treatment' parameter of the run_card
WARNING: Particle 2000001 will use a fake width ( 0.003016558 instead of 0.0003925336 ).
Cross-section will be rescaled according to NWA if needed.To force exact treatment reduce the value of 'small_width_treatment' parameter of the run_card
WARNING: Particle 2000002 will use a fake width ( 0.003018958 instead of 0.001528193 ).
Cross-section will be rescaled according to NWA if needed.To force exact treatment reduce the value of 'small_width_treatment' parameter of the run_card
WARNING: Particle 2000004 will use a fake width ( 0.003018957 instead of 0.002737752 ).
Cross-section will be rescaled according to NWA if needed.To force exact treatment reduce the value of 'small_width_treatment' parameter of the run_card
INFO: Update the dependent parameter of the param_card.dat
ERROR: The width of particle 1000022 is too small for an s-channel resonance (3.47181007e-13). If you have this particle in an s-channel, this is likely to create numerical instabilities .
ERROR: The width of particle 1000023 is too small for an s-channel resonance (9.643513e-11). If you have this particle in an s-channel, this is likely to create numerical instabilities .
ERROR: The width of particle 1000024 is too small for an s-channel resonance (7.102998e-13). If you have this particle in an s-channel, this is likely to create numerical instabilities .
Generating 10000 events with run name run_01
survey run_01
INFO: compile directory
ERROR: The width of particle 1000022 is too small for an s-channel resonance (3.47181007e-13). If you have this particle in an s-channel, this is likely to create numerical instabilities .
ERROR: The width of particle 1000023 is too small for an s-channel resonance (9.643513e-11). If you have this particle in an s-channel, this is likely to create numerical instabilities .
ERROR: The width of particle 1000024 is too small for an s-channel resonance (7.102998e-13). If you have this particle in an s-channel, this is likely to create numerical instabilities .

 I could not find the small_width_treatment in the run card in order to force the exact decay width. Could you please let me know where I could edit this feature?

Best Regards,

Juhi

This is in the run_card.
The line is not display by default but you can add it yourself.

Due to the value of your width for your particles it is more than likely than the results produced by MG5aMC
are not accurate anymore for such small width (just due to numerical precision of the matrix element)

You can reduce the default value of small_width_treatment obviously but do not set it to zero (or lower than 1e-12).

Cheers,

Olivier

> On 21 Nov 2018, at 13:38, Juhi Dutta <email address hidden> wrote:
>
> Question #676252 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/676252
>
> Status: Answered => Open
>
> Juhi Dutta is still having a problem:
> Hi,
>
> I was earlier using version 2.6.2. I checked using v2.6.4, here the
> following warnings were displayed:
>
> WARNING: Particle 1000022 will use a fake width ( 0.0009153118 instead of 3.47181007e-13 ).
> Cross-section will be rescaled according to NWA if needed.To force exact treatment reduce the value of 'small_width_treatment' parameter of the run_card
> WARNING: Particle 1000023 will use a fake width ( -0.000917832 instead of 9.643513e-11 ).
> Cross-section will be rescaled according to NWA if needed.To force exact treatment reduce the value of 'small_width_treatment' parameter of the run_card
> WARNING: Particle 1000024 will use a fake width ( 0.000916197 instead of 7.102998e-13 ).
> Cross-section will be rescaled according to NWA if needed.To force exact treatment reduce the value of 'small_width_treatment' parameter of the run_card
> WARNING: Particle 2000001 will use a fake width ( 0.003016558 instead of 0.0003925336 ).
> Cross-section will be rescaled according to NWA if needed.To force exact treatment reduce the value of 'small_width_treatment' parameter of the run_card
> WARNING: Particle 2000002 will use a fake width ( 0.003018958 instead of 0.001528193 ).
> Cross-section will be rescaled according to NWA if needed.To force exact treatment reduce the value of 'small_width_treatment' parameter of the run_card
> WARNING: Particle 2000004 will use a fake width ( 0.003018957 instead of 0.002737752 ).
> Cross-section will be rescaled according to NWA if needed.To force exact treatment reduce the value of 'small_width_treatment' parameter of the run_card
> INFO: Update the dependent parameter of the param_card.dat
> ERROR: The width of particle 1000022 is too small for an s-channel resonance (3.47181007e-13). If you have this particle in an s-channel, this is likely to create numerical instabilities .
> ERROR: The width of particle 1000023 is too small for an s-channel resonance (9.643513e-11). If you have this particle in an s-channel, this is likely to create numerical instabilities .
> ERROR: The width of particle 1000024 is too small for an s-channel resonance (7.102998e-13). If you have this particle in an s-channel, this is likely to create numerical instabilities .
> Generating 10000 events with run name run_01
> survey run_01
> INFO: compile directory
> ERROR: The width of particle 1000022 is too small for an s-channel resonance (3.47181007e-13). If you have this particle in an s-channel, this is likely to create numerical instabilities .
> ERROR: The width of particle 1000023 is too small for an s-channel resonance (9.643513e-11). If you have this particle in an s-channel, this is likely to create numerical instabilities .
> ERROR: The width of particle 1000024 is too small for an s-channel resonance (7.102998e-13). If you have this particle in an s-channel, this is likely to create numerical instabilities .
>
> I could not find the small_width_treatment in the run card in order to force the exact decay width. Could you please let me know where I could edit this feature?
>
> Best Regards,
>
> Juhi
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Can you help with this problem?

Provide an answer of your own, or ask Juhi Dutta for more information if necessary.

To post a message you must log in.