MadGraph5_aMC@NLO

Evaluation of cross-section in standalone

Asked by Mandeep Kaur

HI! I am evaluating the X-section for the process e+ e- > mu+ mu- case. The matrix squared for the same I can obtain via standalone output mode. As we know that cross-section is just the sum of matrix element squared at all the phase space points. So from the standalone mode if I am getting matrix element squared at different phase space points. Why sum over them not giving me the X-section I am getting using traditional way to calculate it i.e, using phase-space integration.

One possible reason may be that I am not multiplying the each phase-space matrix element squared with its corresponding weight. But I don't know how to get that weight. If this is the case please do tell me how to obtain that?

Thanks

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Olivier Mattelaer (olivier-mattelaer) said : 		#1

Hi,

Yes you have to multiply by the phase-space measure when performing a phase-space integration (which depend of the tool that you use for generating the events to be precise), adding the flux-factor,...

Cheers,

Olivier

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