Different cross section and event generation with different sde_strategy?
I meet some problem in event generation and calculating cross section.
My process is
mu- e- > mu- e- vec
via QED process, where the vec is a massive vector gauge boson that couples with muon and electron.
The diagram is purely QED with a t-channel photon.
This diagram should have no singularity. However, when I try to generate 10,000 events and calculating cross section with sde_strategy=1, I found that if the mass of the vector gauge boson is small, the event generation is slow or event number cannot reach the target. hard_survey cannot save the situation. (large vector boson mass is totally fine)
If I set sde_strategy=2, then it quickly generates 10,000 events and gives me a cross section. However, this cross section is different from the previous one. The previous one is around 3 times larger than this one. I do not believe this is within the uncertainty. The difference of the cross section even exists for the large boson mass case.
Which result should I believe? If I should believe the cross section with the old integral strategy, how can I generate enough number of events? I already tried the parameter hard_survey, or iseed, to the old strategy, but no one works.
Any idea about this?
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- Olivier Mattelaer
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