Integration problem?

Asked by Igal on 2019-08-02

Hi,

I am simulating the following processes: a e- > a a e-. a e- > e- e+ e-, and a e- > a e- e+ e-, the cross-section value calculated by MG deviates a lot from one simulation to another also less than 10% of the LHE events requested are simulated. This problem occurs to my understanding when the integration is diverging particularly at extreme angles. So usually, a remedy is to apply pseudo-rapidity cuts, however this is not a solution for me as I am interested at what is happening at the extreme angles. What is the alternative solution beside pseudo-rapidity cuts to make the integration (and simulation much faster) converging?

Thanks,
 Igal.

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Last query:
2019-08-02
Last reply:
2019-08-02

The only way is to not compute such quantities at lo but to sum over all order. You should therefore check if/which Parton shower program (or resomation one) would correctly handle the computation in the limit of your interest.

Cheers,

Olivier

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From: <email address hidden> <email address hidden> on behalf of Igal <email address hidden>
Sent: Friday, August 2, 2019 5:17:24 PM
To: Olivier Mattelaer <email address hidden>
Subject: [Question #682548]: Integration problem?

New question #682548 on MadGraph5_aMC@NLO:
https://answers.launchpad.net/mg5amcnlo/+question/682548

Hi,

I am simulating the following processes: a e- > a a e-. a e- > e- e+ e-, and a e- > a e- e+ e-, the cross-section value calculated by MG deviates a lot from one simulation to another also less than 10% of the LHE events requested are simulated. This problem occurs to my understanding when the integration is diverging particularly at extreme angles. So usually, a remedy is to apply pseudo-rapidity cuts, however this is not a solution for me as I am interested at what is happening at the extreme angles. What is the alternative solution beside pseudo-rapidity cuts to make the integration (and simulation much faster) converging?

Thanks,
 Igal.

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