0 cross section for ee --> tautau at 20 GeV

Asked by Abner Soffer on 2019-07-02

Hello,

I do the following:

> generate e+ e- > ta+ ta-
> launch

I edit the run card and change the beam energies. If they are 20 GeV each, everything is fine. But setting them to 10 GeV each. The run fails with 0 cross section (See https://cp3.irmp.ucl.ac.be/projects/madgraph/wiki/FAQ-General-14). But this shouldn't happen when sqrt s is 20 GeV and the tau mass is <1.8 GeV.

I also notice that the run card says

#*********************************************************************
# Collider type and energy *
# lpp: 0=No PDF, 1=proton, -1=antiproton, 2=photon from proton, *
# 3=photon from electron *
#*********************************************************************
     0 = lpp1 ! beam 1 type
     0 = lpp2 ! beam 2 type

Suggesting that the beam particles are not e+e- but ppbar. But the html file says e+e-. Why this inconsistency?

Thanks,
Abi

Question information

Language:
English Edit question
Status:
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MadGraph5_aMC@NLO Edit question
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Last query:
2019-07-02
Last reply:
2019-07-02

You have to soften (or fully remove) default cut if you want to go to such low energy.
In this case I believe that the only cut to remove is the "ptl" one.

> I also notice that the run card says
>
> #*********************************************************************
> # Collider type and energy *
> # lpp: 0=No PDF, 1=proton, -1=antiproton, 2=photon from proton, *
> # 3=photon from electron *
> #*********************************************************************
> 0 = lpp1 ! beam 1 type
> 0 = lpp2 ! beam 2 type

The run_card is mainly identical for any type of generation, we have added some dynamical part in the last few years (changing some default value and hiding some of the options which would be meaningless/wrong)
But the run_card is still mainly the same for all type of generation and the comment associated to the parameter reflected that. It is also important that user passing from one generation type to another feel that this is the same configuration file.

Cheers,

Olivier

> On 2 Jul 2019, at 04:52, Abner Soffer <email address hidden> wrote:
>
> New question #681735 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/681735
>
> Hello,
>
> I do the following:
>
>> generate e+ e- > ta+ ta-
>> launch
>
> I edit the run card and change the beam energies. If they are 20 GeV each, everything is fine. But setting them to 10 GeV each. The run fails with 0 cross section (See https://cp3.irmp.ucl.ac.be/projects/madgraph/wiki/FAQ-General-14). But this shouldn't happen when sqrt s is 20 GeV and the tau mass is <1.8 GeV.
>
> I also notice that the run card says
>
> #*********************************************************************
> # Collider type and energy *
> # lpp: 0=No PDF, 1=proton, -1=antiproton, 2=photon from proton, *
> # 3=photon from electron *
> #*********************************************************************
> 0 = lpp1 ! beam 1 type
> 0 = lpp2 ! beam 2 type
>
> Suggesting that the beam particles are not e+e- but ppbar. But the html file says e+e-. Why this inconsistency?
>
> Thanks,
> Abi
>
>
>
>
>
>
>
> --
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> contact for MadGraph5_aMC@NLO.

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