MadGraph5_aMC@NLO

MG5 with fixed target

Asked by s

I am wanting to use MG5 for a fixed target simulation.

I want to simulate a 4Gev electron beam on a Tungsten target. I can work out the target nuclear mass in GeV/c^2 (183*mass of 0.938 GeV/c^2 approx. = 171 GeV/c^2). You can work out then the CoM energy as 174GeV (Ecm = sqrt(me^2 + mN^2+2E*mN)).

So the first thing I did was then set up the two beams to have energy as 174GeV. This produced results. However, I don’t think it is the right way to set this up. I also tried just ebeam1 = 4 GeV, ebeam2 =171 GeV (assumed mass).
This fails to find a cross-section. I also tried setting mbeam1, mbeam2 for masses (0.511, 171) and also having beam (4,171) on various online suggestion but it could not find this definition (Error: no "implicit type”).

What is the best way to simulate a fixed target setup?

Thanks

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Olivier Mattelaer (olivier-mattelaer) said : 		#1

Hi,

I'm not an expert in fixed target experiment. But this would be the way that I would do it in this case.

Assuming that you do not have a specific PDF for the tungsten, then you will need to rescale the one of the proton.
In that case you can do the following:

generate p e- > ve j
output
launch
done
update ion_pdf
set nb_proton1 74
set nb_neutron1 109
set mass_ion1 171
set ebeam1 4
set ebeam2 0
set no_parton_cut
set ptj 10
set fixed_scale 10

If you want to use a dedicated PDF set for that ion then
generate p e- > ve j
output
launch
done
set mass_ion1 171
set ebeam1 4
set ebeam2 0
set no_parton_cut
set ptj 10
set fixed_scale 10
set pdlabel lhapdf
set lhaid XXXXXXX

Cheers,

Olivier

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s (midd1989) said : 		#2

Ah Ok, that makes sense, but how then would you model a scattering process. For example, one background we are worried about is Wide Angle Bremsstrahlung. So, in that case, we need an electron in our final state. I was modeling it like: e- n > e- n f with a scheme similar to the one I described in my initial question. This obviously was not correct

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

Hi,

The first question here, is your process a deep inelastic collision or not.
I guess from the way you write it, this is not a deep inelastic collision.

In that case, you probably need to define an Effective Model where your particle N
is defined (which defines his spin/mass/...). and which defines the interactions with the other particles.
I guess that they are easier way (than doing that/using MG5aMC) in order to simulate such type of collision but as I said I'm not an expert in that field.

Cheers,

Olivier

> On 1 Apr 2020, at 15:37, s <email address hidden> wrote:
>
> Question #689622 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/689622
>
> Status: Answered => Open
>
> s is still having a problem:
> Ah Ok, that makes sense, but how then would you model a scattering
> process. For example, one background we are worried about is Wide Angle
> Bremsstrahlung. So, in that case, we need an electron in our final
> state. I was modeling it like: e- n > e- n f with a scheme similar to
> the one I described in my initial question. This obviously was not
> correct
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

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