cross section problem

Hi,

Here is the value that I get without decay

q q~ > z z : 9.358
p p > z w+: 15.46
p p > z w-: 9.311

Adding the decay do not change anything to the picture here since the NWA works pretty well.
Why are you trouble by those numbers? I found natural to have those number of the same order of magnitude.
Could you explain why you do not trust such number?

Cheers,

Olivier

> On Aug 16, 2016, at 13:57, Olympia <email address hidden> wrote:
>
> New question #346312 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/346312
>
> Hi,
>
> I generate 3 different SM process :
>
> 1) p p > z z, z> mu+ mu- , z> q q~
> 2) p p > w+ z ,z> mu+ mu- , w+> q q~
> 3) p p > w- z ,z> mu+ mu- , w-> q q~
>
> where q and q~ are defined in every process as all the possible combinations of quarks and anti-quarks. My problem is that the cross section in all these processes are very close! and that is impossible! I didn't do any change in the run_card or in any other card. Do you have any idea what will be the solution?
>
> Thank you in advance.
> Olympia
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Hi,

with the processes that I generate I take the following cross section:

1)0.41 pb
2) 0.34 pb
3)0.201 pb
thats why I do not trust the numbers, for the decays that I have I expect bigger cross section according to the branching ratio of every individual decay.

Thanks,
Olympia

Hi,

Not sure to understand your point.

from the numbers quoted in my previous email and from the following BR:
Z > mu+ mu-: 3.438731e-02
Z > j j : 69%
W+> j j: 66%

you expect the following cross-section
ZZ to be 0.4440790968324
W+Z: 0.3540641231916
W-Z: 0.21324004211105999

This is sounds close enough to me from your result given:
- the 2% statistical uncertainty
- the 5% theoretical uncertainty of the narrow width approximation.
- the 8% scale uncertainty

So I do not see any reason to be worried here.

Cheers,

Olivier

> On Aug 17, 2016, at 12:47, Olympia <email address hidden> wrote:
>
> Question #346312 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/346312
>
> Olympia posted a new comment:
> Hi,
>
> with the processes that I generate I take the following cross section:
>
> 1)0.41 pb
> 2) 0.34 pb
> 3)0.201 pb
> thats why I do not trust the numbers, for the decays that I have I expect bigger cross section according to the branching ratio of every individual decay.
>
> Thanks,
> Olympia
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Hi,

according to this paper https://cds.cern.ch/record/2113195/files/ATL-COM-PHYS-2015-1502.pdf I expect bigger total cross section at 13TeV. And for the ZZ we expect 10times lower( not published yet). So it seems that with madgraph we have only? LO calculation.

Cheers,
Olympia

Dear Olympia,

> according to this paper https://cds.cern.ch/record/2113195/files/ATL-
> COM-PHYS-2015-1502.pdf I expect bigger total cross section at 13TeV. And
> for the ZZ we expect 10times lower( not published yet).

I’m not part of atlas collaboration and I therefore have no access to that paper. Therefore, I can not comment on it.
(at least I do not the authorization to read it).

But If i look at the CMS reported number. See for example here:
https://twiki.cern.ch/twiki/pub/CMSPublic/PhysicsResultsCombined/SigmaNew_v0.pdf
The ZZ is clearly not 10 times lower. (and here they report ZW+ and ZW- combined)

> So it seems that with madgraph we have only? LO calculation.

Our code is able to do both LO and NLO computation (and loop-induced LO computation)
Your syntax indeed generate the LO calculation.

If you want the NLO computation, you have to generate
generate p p > Z Z [QCD]
generate p p > Z W+ [QCD]
generate p p > Z W- [QCD]
the decay of the weak boson can be performed by madspin.

Here is the cross-section computed @NLO:
ZZ: 1.359e+01
ZW+ : 2.720e+01
ZW- : 1.730e+01

If you are interested in the g g > Z Z contribution (which is technically part of the NNLO).
This can also be computed with MG5aMC (it was reported here: http://arxiv.org/pdf/1507.00020.pdf)
and is at 1.313 pb

This sounds inline with the CMS results reported above.

Cheers,

Olivier

> On Aug 18, 2016, at 14:22, Olympia <email address hidden> wrote:
>
> Question #346312 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/346312
>
> Olympia posted a new comment:
> Hi,
>
> according to this paper https://cds.cern.ch/record/2113195/files/ATL-
> COM-PHYS-2015-1502.pdf I expect bigger total cross section at 13TeV. And
> for the ZZ we expect 10times lower( not published yet). So it seems
> that with madgraph we have only? LO calculation.
>
>
> Cheers,
> Olympia
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.