Cross-section decreasing with increase in uncorrelated coupling

Asked by Lopamudra Mukherjee on 2018-02-06

Dear MadGraph team,

I have a model in which I am looking at pp collision leading to a final state of tauons along with missing energy via some BSM fermion. This process should be independent of coupling between the BSM particle with muons. However, when I am changing this coupling, the cross-section is decreasing (which should not be the case, because it is independent of the muon coupling). The process is following :

MG5_aMC> generate p p > ttl- TTl+ , (ttl- > ta- h2 ) , (TTl+ > ta+ h2)

ttl-/TTl+ are the BSM fermions and h2 is the BSM scalar.

I am unable to resolve this issue. Please help!
Thank you.

Question information

Language:
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Status:
Solved
For:
MadGraph5_aMC@NLO Edit question
Assignee:
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Solved by:
Olivier Mattelaer
Solved:
2018-02-07
Last query:
2018-02-07
Last reply:
2018-02-07

Hi,

I will not be able to look into this before tomorrow.
But with that few information they are simply nothing that I can do.

1) what is the model that you are using (if it is not one of the auto-downloadable, please put it somewhere online where I can have access to it)
2) what is the two(or more) benchmark point that you are using to observe such weird behavior?

Cheers,

Olivier

> On 6 Feb 2018, at 13:26, Lopamudra Mukherjee <email address hidden> wrote:
>
> New question #664133 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/664133
>
> Dear MadGraph team,
>
> I have a model in which I am looking at pp collision leading to a final state of tauons along with missing energy via some BSM fermion. This process should be independent of coupling between the BSM particle with muons. However, when I am changing this coupling, the cross-section is decreasing (which should not be the case, because it is independent of the muon coupling). The process is following :
>
> MG5_aMC> generate p p > ttl- TTl+ , (ttl- > ta- h2 ) , (TTl+ > ta+ h2)
>
> ttl-/TTl+ are the BSM fermions and h2 is the BSM scalar.
>
> I am unable to resolve this issue. Please help!
> Thank you.
>
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Hi,

Thanks for the model
I have run the following run
import model Mod_InertDoublet_UFO
generate p p > ttl- TTl+ , (ttl- > ta- h2 ) , (TTl+ > ta+ h2)
output
launch
set le scan:[1e-3,1.0]
set lm scan:[1e-1,1.0]

Here is the results of such scan:
#run_name bsm#1 bsm#2 cross(pb)
run_03 1.000000e-03 1.000000e-01 7.648288e-03
run_04 1.000000e-03 1.000000e+00 7.661010e-03
run_05 1.000000e+00 1.000000e-01 7.643789e-03
run_06 1.000000e+00 1.000000e+00 7.645321e-03

So you can see that indeed the cross-section is independent of your coupling.

Now I have also run the following script:

import model Mod_InertDoublet_UFO
generate p p > ttl- TTl+ , (ttl- > ta- h2 ) , (TTl+ > ta+ h2)
output
launch
set le scan:[1e-3,1.0]
set lm scan:[1e-1,1.0]
set wttl Auto

and the associate result is:

#run_name bsm#1 bsm#2 cross(pb)
run_07 1.000000e-03 1.000000e-01 1.178390e+00
run_08 1.000000e-03 1.000000e+00 2.416247e-01
run_09 1.000000e+00 1.000000e-01 2.390647e-01
run_10 1.000000e+00 1.000000e+00 9.984530e-02

So as you can see, the cross-section depends on the total width and the total width seems to depend of the value of the coupling.

Cheers,

Olivier

Lopamudra Mukherjee (madgraph) said : #3

Thank you so much. This really helped me a lot. I was setting the decay width to Auto which is why I was obtaining such behaviour.

Cheers,

Lopamudra