MadGraph5_aMC@NLO

Inconsistency between using EPPS16_208 and set PbPb

Asked by Hesham El Faham

Hi,
I am using a new physics model with a new ALP particle called "ax". I am simulating this process as follows:
generate p p > ax > mu+ mu-
I am performing the simulation in pp and in PbPb collisions. I expect a roughly 10^4 gain in the xsec for the latter.

I immediately get this gain when I use set PbPb.

However, when I use EPPS16_208 via the following commands (the pdf is not scaled so I modify the beam energies):
-set pdlabel lhapdf
-set lhaid 901300
-set ebeam1 2750*208
-set ebeam2 2750*208
I don't get the 10^4 gain unless the ax is very high in mass. At ax = 2GeV for example, the pp and the PbPb cross-sections are almost the same. Even at ax=10GeV, the difference between both cross sections is a barely one order of magnitude.

I am wondering if that is understood, as I want to decide which way is the correct way of simulating PbPb in mg5. Thanks!

Best,
Hesham

Question information

Language:
English Edit question
Status:
Solved
For:
MadGraph5_aMC@NLO Edit question
Assignee:
No assignee Edit question
Solved by:
Olivier Mattelaer
Solved:
Last query:
Last reply:
Revision history for this message
Best Olivier Mattelaer (olivier-mattelaer) said : 		#1

Hi,

My understanding of https://www.jyu.fi/science/en/physics/research/highenergy/urhic/npdfs/epps16-nuclear-pdfs
is that you do not need to multiply the beam energy by "208" by that you have to multiply the cross-section by 208**2
However I'm not an expert of that pdf set.

Cheers,

Olivier

> On 21 Jun 2021, at 11:00, Hesham El Faham <email address hidden> wrote:
>
> New question #697636 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/697636
>
> Hi,
> I am using a new physics model with a new ALP particle called "ax". I am simulating this process as follows:
> generate p p > ax > mu+ mu-
> I am performing the simulation in pp and in PbPb collisions. I expect a roughly 10^4 gain in the xsec for the latter.
>
> I immediately get this gain when I use set PbPb.
>
> However, when I use EPPS16_208 via the following commands (the pdf is not scaled so I modify the beam energies):
> -set pdlabel lhapdf
> -set lhaid 901300
> -set ebeam1 2750*208
> -set ebeam2 2750*208
> I don't get the 10^4 gain unless the ax is very high in mass. At ax = 2GeV for example, the pp and the PbPb cross-sections are almost the same. Even at ax=10GeV, the difference between both cross sections is a barely one order of magnitude.
>
> I am wondering if that is understood, as I want to decide which way is the correct way of simulating PbPb in mg5. Thanks!
>
> Best,
> Hesham
>
>
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Revision history for this message
Hesham El Faham (helfaham) said : 		#2

Thanks Olivier Mattelaer, that solved my question.