Generating pp --> Z -->4l

Hi,

The problem is that using add process, you do not include the interference between those Feynman Diagram.

> is there an issue with forcing this unphysical subset of diagrams?

If you subset is not gauge invariant. Then our result will not have any meaning and will also breaks lorentz invariance.
So yes this might be problematic in general.

> how I can generate this process correctly?

you can try this syntax:
generate p p > e+ | e- | mu+ | mu- > e+ e- mu+ mu-

Cheers,

Olivier

> On Feb 22, 2016, at 12:51, Kenneth Long <email address hidden> wrote:
>
> New question #286487 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/286487
>
> Hi Experts,
>
> I expect this has probably been addressed before, but I'm having a hard time tracking down the information. Essentially I want to reproduce figure 2 here:
>
> http://arxiv.org/pdf/1107.5051v3.pdf
>
> Where the pp --> 4l cross section is compared to calculations treating only the "single-resonant" (pp --> Z/gamma* --> 4l) and "double-resonant" (pp --> Z/gamma*Z/gamma* --> 4l) contributions. I tried to generate these processes with the following syntax:
>
> Total: p p > e+ e- mu+ mu-
> Sigma = 192 fb
>
> Double resonant: p p > e+ e- mu+ mu- \ e+ e- mu+ m-
> Sigma = 87 fb
>
> Single resonant: p p > e+ > e+ e- mu+ mu-
> add process p p > e- > e+ e- mu+ mu-
> add process p p > mu+ > e+ e- mu+ mu-
> add process p p > mu- > e+ e- mu+ mu-
> Sigma = 283 fb
>
> So clearly something is off in the single-resonant production: https://kelong.web.cern.ch/kelong/DibosonAnalysisData/PlottingResults/ZZGenAnalysis/isHardProcess/2016-02-22/13h44/4lmass.pdf
>
> Though it looks like the Feynman diagrams generated are what I was intending: https://kelong.web.cern.ch/kelong/Diagrams/singleres_eemm/HTML/info.html
>
> Is this the correct syntax, or is there an issue with forcing this unphysical subset of diagrams? Do you have a suggestion on how I can generate this process correctly?
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Hi Olivier,

Ah, so each "add process" line is treated completely independently without interference?

In any case, this looks good, thanks!

https://kelong.web.cern.ch/kelong/DibosonAnalysisData/PlottingResults/ZZGenAnalysis/isHardProcess/2016-02-22/15h40/4lmass.pdf

Best,

Kenneth

> Ah, so each "add process" line is treated completely independently
> without interference?

Correct.

Olivier
> On Feb 22, 2016, at 14:47, Kenneth Long <email address hidden> wrote:
>
> Question #286487 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/286487
>
> Status: Answered => Solved
>
> Kenneth Long confirmed that the question is solved:
> Hi Olivier,
>
> Ah, so each "add process" line is treated completely independently
> without interference?
>
> In any case, this looks good, thanks!
>
> https://kelong.web.cern.ch/kelong/DibosonAnalysisData/PlottingResults/ZZGenAnalysis/isHardProcess/2016-02-22/15h40/4lmass.pdf
>
> Best,
>
> Kenneth
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Hi Kenneth and Olivier,
         If I could understand the problem then someone can also use :

generate p p > z > e+ e- mu+ mu- QED=99
output <file name>
display diagrams

                (for single resonance where you suppose to add all the process into account which may contain photon at the same time .)

and

generate p p > z z, (z > e+ e-, z > mu+ mu-) QED=99 (for double resonance)
output <file name>
display diagrams

P.S. : Display diagrams or any other calculations must be after "output " command for your required process .

Request : Let me know if it works and able to match with the existing result .

Thanks,

Subhasish

Hi Subhasish,

I can answer and Olivier can correct me if I say something imprecise. I first tried to use the syntax you suggest for the single-resonant contribution. The resulting Feynman diagrams are here: https://kelong.web.cern.ch/kelong/Diagrams/Z-a_eemm/

As you see, this also includes the double resonant contribution. My understanding is that this syntax forces a z to be in the s-channel, but it does not make an exclusive requirement, i.e. the double resonant contributions are included. The only exclusion with respect to the the total 4l production is diagrams with two s-channel gamma*'s.

In the end the syntax suggested by Olivier was exactly what I was looking for: https://kelong.web.cern.ch/kelong/Diagrams/singleres_eemm/

The syntax you suggest for the double resonant contribution requires that the Z be on-shell +- the bw_cut in the run card, so the gamma* contribution is not included. I therefore preferred the syntax to exclude leptons in the s-channel.

Best,

Kenneth