Issue with decay product cuts for LO cross section

Hi,

I do not understand your statement about "decay product".
If you were generating with decay product lets stay
p p > h z , h > a a , z > b b~
then indeed you would not need any cut and the cross-section would be finite.

But your computation is technically part of the NNLO calculation (in QED)
of q q~ > b b~ (part of the double real emission).
So this is/should be inifinite without cuts.

> Additionally, it would be good to compare the cross section with the results that I got from calculating this process at NLO fixed order (no event generation, process p p > b b~ a a [QCD]. For this process, I was able to get results without any cuts (obviously because there are no decay products generated). What cuts should I use to best mimic the NLO calculation?

As said above, without cuts the correct result is +infinity
This is obviously a result that we can not achieve numerically.
The conclusion is that you have cuts (likely via the jet definition).

Cheers,

Olivier

> On 18 Dec 2023, at 17:55, Radha Mastandrea <email address hidden> wrote:
>
> New question #708750 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/708750
>
> I am trying to generate events and calculate the LO cross section for the process p p > b b~ a a (MadGraph version 3.5.1). I currently have no cuts on the decay products, and the cross section calculation fails with the error
>
> Note: The following floating-point exceptions are signalling: IEEE_INVALID_FLAG IEEE_DIVIDE_BY_ZERO IEEE_OVERFLOW_FLAG IEEE_UNDERFLOW_FLAG IEEE_DENORMAL
> STOP 1
> rm: cannot remove 'results.dat': No such file or directory
> ERROR DETECTED
>
> I know that some cuts are necessary for this process in order to get meaningful results, but I am not sure exactly what cuts to do -- ideally I would like the softest possible cuts on the decay products, but testing a few pt cuts on the final state photons seems to lead to wildly different results in the cross section calculation.
>
> Additionally, it would be good to compare the cross section with the results that I got from calculating this process at NLO fixed order (no event generation, process p p > b b~ a a [QCD]. For this process, I was able to get results without any cuts (obviously because there are no decay products generated). What cuts should I use to best mimic the NLO calculation?
>
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