Z' cross section difference between basf2 and standalone MG using model taudecay_UFO

Hi,

What is the cross-section if you do not decay your Z prime?
Which value did you put for the total width of the Z prime?

Is bfast2 is using simple branching ratio for that? (we do not and need to have to total width correct due to that)

I see that in the MG5 command file you use:
> set WZp 'auto'

You should have a warning in your log like this:
WARNING: Invalid input: Expected number and not ''auto''
Do you have that?
You should rather use
> set WZp auto

Which should not produce such warning.

This also means that you are likely fail to use the correct width in our code.

Cheers,

Olivier

> On 21 Jun 2019, at 18:38, Igna <email address hidden> wrote:
>
> New question #681528 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/681528
>
> I'm looking into case 1. ee > tautauZ' [ > mumu] and case 2. ee > mumuZ' [ > tautau]. I need the correct cross-section of the events.
>
> I used method 1. basf2 and method 2. madgraph (version 2.6.5) to generate the processes, based on files I found online on desy and on the belle2 server. I'm attaching the files I used to generate both cases and both methods below. The difference between methods is that for basf2 I used just model Lmu_minus_Ltau_UFO, but for madgraph I additionally used model taudecay_UFO.
>
> When calculating the cross sections for various Z' masses (and otherwise identical parameters), the two methods give results of different magnitude (up to 10^3), as you can see in the attached plot. The values on the y-axis (cross-section) are in femtobarns and on the x-axis (Z' mass) in GeV/c^2. The pink line in the plot is for older values, obtained from my supervisor.
>
> CROSS SECTION PLOT : https://drive.google.com/open?id=1OWNTqFlEucnY36WGXiHdLEX51Tm-BrSz
>
> CASE 1 METHOD 1: https://drive.google.com/open?id=1AOwjadX2u5Qurl5G_H3XsuYE8vQMUjfB
>
> CASE 1 METHOD 2: https://drive.google.com/open?id=1x8MZkQq5OJhIOUEBc_F-HnsK21-GSHeY
>
> CASE 2 METHOD 1: https://drive.google.com/open?id=1zW4iS3wJT0clxcTR4Se5udzuE1q8QDS5
>
> CASE 2 METHOD 2: https://drive.google.com/open?id=1lIFgRB3tJ-vI2TPhq2mima_HbHxjm_zQ
>
> Thank you and let me know if you need additional information.
>
> --
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> contact for MadGraph5_aMC@NLO.

Hi,

If I don't specify the Z' decay, the ee->mumuZ' cross-sections overlap for the two methods (and with the presumed correct plot from my supervisor), but the ee->tautauZ' cross-sections stay almost the same as initially - see the plot I'm attaching. So the problem comes from the taus, not from Z', as far as I can tell.

Isn't the total width the parameter WZp, which I set on auto? When I remove the quotations, the cross-section values become ~ten times bigger, but they still don't coincide with any other plot.

Would you generate my processes in any way differently than I did? And in general, how could I check if they were generated correctly? The Feynman diagrams and the variables in the ttrees look fine, my only issue is the cross-sections.

I'm not sure what basf2 uses for a branching ratio, but I will update as soon as I figure out anything relevant, thank you a lot for the reply!

CROSS SECTION WITHOUT DECAYING Z': https://drive.google.com/open?id=1_0550ERc4KILjN_HVC-2Vdi_YoZbQ2av

Hi,

Isn't the total width the parameter WZp, which I set on auto? When I
remove the quotations, the cross-section values become ~ten times
bigger, but they still don't coincide with any other plot.

the command
set WZP 'auto'
does not do anything (i.e. WZP is still the default width of the model)
while
set WZP auto
use the program describe in arXiv:1402.1178<http://arXiv.org/abs/arXiv:1402.1178> (where the limitation of that code are described)

Would you generate my processes in any way differently than I did?

Maybe, I do not know the bfast2 code (first time I hear about it).
So I do not know what effect that they include. Since it sounds a wrapper around MG5aMC, they should include some additional physics compare to MG5aMC.

If I don't specify the Z' decay, the ee->mumuZ' cross-sections overlap
for the two methods (and with the presumed correct plot from my
supervisor), but the ee->tautauZ' cross-sections stay almost the same as
initially - see the plot I'm attaching. So the problem comes from the
taus, not from Z', as far as I can tell.

Looks like the following FAQ might give you some inside.
https://answers.launchpad.net/mg5amcnlo/+faq/2442
The more likely culprint is either cut or the value of the total width.

Cheers,

Olivier

On 22 Jun 2019, at 17:03, Igna <<email address hidden><mailto:<email address hidden>>> wrote:

Question #681528 on MadGraph5_aMC@NLO changed:
https://answers.launchpad.net/mg5amcnlo/+question/681528

Igna posted a new comment:
Hi,

If I don't specify the Z' decay, the ee->mumuZ' cross-sections overlap
for the two methods (and with the presumed correct plot from my
supervisor), but the ee->tautauZ' cross-sections stay almost the same as
initially - see the plot I'm attaching. So the problem comes from the
taus, not from Z', as far as I can tell.

Isn't the total width the parameter WZp, which I set on auto? When I
remove the quotations, the cross-section values become ~ten times
bigger, but they still don't coincide with any other plot.

Would you generate my processes in any way differently than I did? And
in general, how could I check if they were generated correctly? The
Feynman diagrams and the variables in the ttrees look fine, my only
issue is the cross-sections.

I'm not sure what basf2 uses for a branching ratio, but I will update as
soon as I figure out anything relevant, thank you a lot for the reply!

CROSS SECTION WITHOUT DECAYING Z': https://drive.google.com/open?id=1_0550ERc4KILjN_HVC-2Vdi_YoZbQ2av

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Hi,

I should have mentioned basf2 uses MG, sorry for the confusion, I am rather new to everything. I will compare the run cards in detail and when (if) I find out for sure which cross-section is correct, I will update this threat. Thank you for the resources provided and for telling me about the quotation marks for 'auto'!

Enjoy your weekend!

Thanks Olivier Mattelaer, that solved my question.