MadGraph5_aMC@NLO

pn collisions

Asked by Georgios Krintiras

Dear experts,

I am a CMS member and I would like to generate proton nucleus (pA) collisions for inclusive tt production. That would be useful for future studies of tt in proton Lead (Pb) collisions, hence I would like to check whether it is possible to generate on top of pp also pn collisions and use different PDF sets for the incoming particles, i.e. for the proton and the neutron.

Regards,

Georgios K Krintiras

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

Hi,

We are thinking to add such possibilities but this is not possible for the moment.

Cheers,

Olivier

PS: I would advise to use re-weighting method to achieve the same effect.

> On 23 May 2017, at 16:04, Georgios Krintiras <email address hidden> wrote:
>
> New question #633707 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/633707
>
> Dear experts,
>
> I am a CMS member and I would like to generate proton nucleus (pA) collisions for inclusive tt production. That would be useful for future studies of tt in proton Lead (Pb) collisions, hence I would like to check whether it is possible to generate on top of pp also pn collisions and use different PDF sets for the incoming particles, i.e. for the proton and the neutron.
>
>
> Regards,
>
> Georgios K Krintiras
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

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Georgios Krintiras (gkrintir) said : 		#2

Thanks Olivier,

Right, re-weighting is a solution though it doesn't take into account the effect from nuclear PDF.

Thanks for letting me know that it's under your considerations ;D

Regards

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Georgios Krintiras (gkrintir) said : 		#3

Thanks Olivier Mattelaer, that solved my question.

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Olivier Mattelaer (olivier-mattelaer) said : 		#4

Hi,

> Right, re-weighting is a solution though it doesn't take into account the effect from nuclear PDF.

No it does.
You just have to reweight each event by "f(nuclear)/f(proton)" and you will get the correct distribution.
You can also implement such ratio as a plugin (for LO only): https://cp3.irmp.ucl.ac.be/projects/madgraph/wiki/Plugin
if you want to keep un-weighted events.

(Note that for NLO, in order to have the correct re-weighting you have to keep the full information, i.e. set in the run_card:
"store_rwgt_info" on True)

Cheers,

Olivier

PS: One easy way to implement such reweighting that is to modify the file "systematics.py" which performs very similar type of re-weighting.

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Georgios Krintiras (gkrintir) said : 		#5

Ah ok now I got your point of reweighting based on f(nuclear)/f(proton) !

Thanks also for the tip of modifying the systematics.py ;D

Regards