MadGraph5_aMC@NLO

compare with pythia

Asked by saeedeh

Hi

I was faced a problem .

I have paper with these information |y_gamma|<1 180<pt_gamma<300 |eta_jet|<1.5 for process p p > a c contains prediction of pythia :
it includes only 2 -> 2 matrix element g c > a c and q~ q > a g scatterings followed by g > c~ c spliting in the parton shower

prediction of pythia this process is 4.01 * 10^-4

for this processs with madgraph :

I define q = u d s c u~ s~ d~ c~
generate g c > a c
add process g c~ > a c~
add process q q > a g , g > c~ c

Is it true? (my result is very small than pythia result)

Thanks,

Saeedeh

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Olivier Mattelaer
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Olivier Mattelaer (olivier-mattelaer) said : 		#1

Hi Saeedeh,

The correct syntax for what you want to do is
> generate g c > a c
> add process g c~ > a c~
> add process q q > a c~ c

The g , g > syntax forces the gluon to be “on shell — up to x times the width—“ so this is meaningless in this case.

Please read the following tutorial:
https://cp3.irmp.ucl.ac.be/projects/madgraph/attachment/wiki/MGTalks/13_06_10_tutomg_tasi.pdf

Cheers,

Olivier

On Mar 8, 2014, at 6:06 PM, saeedeh <email address hidden> wrote:

> New question #245185 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/245185
>
> Hi
>
> I was faced a problem .
>
> I have paper with these information |y_gamma|<1 180<pt_gamma<300 |eta_jet|<1.5 for process p p > a c contains prediction of pythia :
> it includes only 2 -> 2 matrix element g c > a c and q~ q > a g scatterings followed by g > c~ c spliting in the parton shower
>
> prediction of pythia this process is 4.01 * 10^-4
>
>
> for this processs with madgraph :
>
> I define q = u d s c u~ s~ d~ c~
> generate g c > a c
> add process g c~ > a c~
> add process q q > a g , g > c~ c
>
> Is it true? (my result is very small than pythia result)
>
>
> Thanks,
>
> Saeedeh
>
>
>
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Revision history for this message
saeedeh (dorado-luminous) said : 		#2

Hi
thank you for your help
but steel my result is smaller than phytia

for 180<pt_gamma<300 cross section of Madgraph is 1*10^-4 but cross section of phytia is 4*10^-4
also for 30<pt_gamma<40 I have \sigma=3.9 and for phytia \sigma=6.55

I used cteq6l1 as same as phytia

Cheers,

Revision history for this message
Best Olivier Mattelaer (olivier-mattelaer) said : 		#3

Hi,

Now this sounds reasonable and the difference should be due to a parametrization differences.
- Did you check which scale is used in both cases?
- Did they run in four flavor as well?
- Is all the mass set to zero also in their case?

Cheers,

Olivier

On Mar 12, 2014, at 10:41 AM, saeedeh <email address hidden> wrote:

> Question #245185 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/245185
>
> Status: Answered => Open
>
> saeedeh is still having a problem:
> Hi
> thank you for your help
> but steel my result is smaller than phytia
>
> for 180<pt_gamma<300 cross section of Madgraph is 1*10^-4 but cross section of phytia is 4*10^-4
> also for 30<pt_gamma<40 I have \sigma=3.9 and for phytia \sigma=6.55
>
> I used cteq6l1 as same as phytia
>
> Cheers,
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Revision history for this message
saeedeh (dorado-luminous) said : 		#4

Thanks Olivier Mattelaer, that solved my question.