# Integration problem?

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.

## Question information

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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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Subject: [Question #682548]: Integration problem?

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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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