Cross-section discrepancy involving resonance

Well difficult to tell. my first guess would be the width.

How did you implement the width?

Cheers,

Olivier

> On 11 Mar 2019, at 02:03, Sebastian Urrutia-Quiroga <email address hidden> wrote:
>
> New question #679100 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/679100
>
> Hi all,
> I'm calculating a scattering LNV process (e+ h- > e- h+, with h+ a charged scalar) involving the interference of both an s- and t-channels. I want to compare my analytic result with MG for different values of sqrt(s), and they agree except for the center-of-mass energy of an on-shell production of the s-channel particle.
> Do you know what is the possible source of this discrepancy? I've tried to change some options and cuts, especially bwcutoff and cut_decays, but I still don't get the reason.
>
> Any suggestion is welcome. Thank you in advance,
> Sebastian
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Hi Olivier,
Thank you for your quick reply. I'm asking MG to calculate the width automatically (set WF Auto, where F is the s-channel particle).

Best,
Sebastian

If you are using the same value of the width in your analytical computation, then I have no idea.

Cheers,

Olivier

Yes, I'm using the same value in both methods.

Anyway, thank you so much!
Sebastian

Hi Olivier,
I'm wondering if there is a special condition for the resonance if the intermediate state is a Majorana fermion, i.e. e- h+ > nR > e+ h-.
In my analytical calculation, I'm using the propagator's denominator as s - M_nR^2 + i M_nR Gamma_nR.

Thank you so much,
Sebastian

Hi,

Majorana fermion are special in general but nothing specific occurs when such particles are onshell/

In my analytical calculation, I'm using the propagator's denominator as s - M_nR^2 + i M_nR Gamma_nR.

That's the default denominator for UFO model (if the UFO model does not ask us to use another one and/or if you did not ask to run in the complex-mass scheme.)
If you use a old model format (called MADGRAPH v4), then the default is slightly different if I remember correctly (but I doubt that you use such format for your model)

Cheers,

Olivier

 (if the UFO model does not ask us to use another one and/or if you did not ask to run in the complex-mass scheme.

Hi Olivier,

I see, thank you so much,

Sebastian

Hi Olivier,
I'm sorry to keep bothering you with the same topic, but I did a detailed scan around the resonance and I noticed that both the analytical and MG5 results are just shifted with respect to each other: http://prntscr.com/n0r7dm

Considering this fact now, do you have any idea about why this is happening?

Thank you so much,
Sebastian

My best bet would be a plotting issue.
That you variable "S" is not the same in your analytical computation and in MG5aMC.
In particular related to the fact that your particles are not massless (is the electron massive or massless).

The shift is actually very small ( and much smaller than any experimental shift/theoretical shift due to NLO precision). So this can be in principle created by a lot of stuff, interference, sign of the width,....

Cheers,

Olivier

> On 21 Mar 2019, at 01:46, Sebastian Urrutia-Quiroga <email address hidden> wrote:
>
> Question #679100 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/679100
>
> Sebastian Urrutia-Quiroga posted a new comment:
> Hi Olivier,
> I'm sorry to keep bothering you with the same topic, but I did a detailed scan around the resonance and I noticed that both the analytical and MG5 results are just shifted with respect to each other: http://prntscr.com/n0r7dm
>
> Considering this fact now, do you have any idea about why this is
> happening?
>
> Thank you so much,
> Sebastian
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Hi again,
Thank you so much!

Best,
Sebastian