Cuts for fixed-target collisions

Asked by Gennaro Corcella on 2019-04-26

Hello,

I have been simulating a process where a positron beam of 550 MeV hits on an electron fixed target.
I wish to ask you whether I can straightforwardly set the cuts in run_card.dat in the laboratory frame.

In fact, in the default run card I read that the energy cuts are applied in the centre-of-mass frame.
What about the other cuts, e.g., on rapidity and transverse momentum?

Shall I apply any Lorentz transform from the lab to the centre-of-mass frame in order to get the cuts in the centre-of-mass frame before editing the run card?

Thanks, Gennaro

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2019-04-26
Last reply:
2019-04-26

Hi,

> I wish to ask you whether I can straightforwardly set the cuts in run_card.dat in the laboratory frame.

No this is not trivial.

> In fact, in the default run card I read that the energy cuts are applied in the centre-of-mass frame.
> What about the other cuts, e.g., on rapidity and transverse momentum?

The rapidity cut is actually in the lab-frame.
The transverse momentum is the same in both frame and therefore is technically applied in the center or mass frame but that does not matter.

> Shall I apply any Lorentz transform from the lab to the centre-of-mass frame in order to get the cuts in the centre-of-mass frame before editing the run card?

All the cuts (but the rapidity) are in the center-of-mass frame.
So you do not need anything here. Setting the rapidity cut in the center of mass frame is possible.

I would strongly advise against modifying the meaning (including the frame) of any of the cuts defined in the run_card. The reason is that such parameters are also used to optimise the phase-space generation and that can then lead to bias if you change the meaning.

Cheers,

Olivier

> On 26 Apr 2019, at 13:27, Gennaro Corcella <email address hidden> wrote:
>
> New question #680467 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/680467
>
> Hello,
>
> I have been simulating a process where a positron beam of 550 MeV hits on an electron fixed target.
> I wish to ask you whether I can straightforwardly set the cuts in run_card.dat in the laboratory frame.
>
> In fact, in the default run card I read that the energy cuts are applied in the centre-of-mass frame.
> What about the other cuts, e.g., on rapidity and transverse momentum?
>
> Shall I apply any Lorentz transform from the lab to the centre-of-mass frame in order to get the cuts in the centre-of-mass frame before editing the run card?
>
> Thanks, Gennaro
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

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