Comment 4 for bug 2022069

So the real problem here is that the efficiency of the method is super low.
I only have the one estimated after 10 events so far and it is critically low
INFO: decaying event number 10. Efficiency: 102.44444444444444 [2.391008138656616 s]
(so this means that we do generate ~100 unweighted events (of the decay type) to get one valid for each of the production.

So if you want to do 80k production event, we need to generate 80k*100 = 80M decay events.
We do split such generation by batch of ~60k which means that we do have many batches and in rare occasion some batches fail to reach target. I would not worry too much about that as long as it is exceptional.

On the other hand, I would worry on why the efficiency is so small. This likely means that the method is breaking (you do expect to have the efficiency between 2 and 8 in general for this method) and the most typical reason is that NWA is not valid.

I guess that the issue here should be related to the presence of identical particle.
Indeed the onshell mode rely on the re-weighting module which does not support correctly identical particle between decay and production (impossible to identify correctly which one is which). This has been improved
in version 3.4.0 where the reweighting mode allow to average over all combination. And this averaging mode should be the default for onshell mode in madspin in 3.4.0. I have tried 3.5.2 and efficiency is also bad so this is likely not solving the issue in this case (maybe because the width are so small that we do have numerical issue when evaluating the matrix-element even for the correct combination).

In any case, which version of MG5aMC did you use?

Cheers,

Olivier