[Common] RecoDecay: Add matching for decaying tracks in getMatchedMCRec

[Luca610]

This PR introduces the option to match cases with one or more decayed tracks in the function getMatchedMCRec.
@vkucera let me know if it works for you!

[vkucera]

Hi @Luca610 , please elaborate more about the problem you are trying to tackle with this implementation and why getMatchedMCRec is the right place to put it. To be honest, from the first look, I don't like the idea of adding this very species-specific feature inside a generic matching method if it doesn't solve a problem that cannot be done outside and doesn't improve the matching result either.

[Luca610]

Hi @vkucera, when trying to match some decay such as K0s->pi+pi- it was observed that some reconsructed particles where not correctly matched causing a visible peak in the invariant mass distribution of unmatched candidates. This is caused by the fact that one of the pions decayed into a muon during the simulation and the track is then associated to a mu. For a reference, this is the case of around 2% of K0s. I beleive the same could happen with K->pi. I think that this could be the place to add it because many analyses could profit from it, preventing code duplication.

[vkucera]

Hi @Luca610 , thanks for the details. Are you saying that in our simulations, tracks of pions which decay to muons are wrongly associated with the daughter muons instead of with the pions?
If that is so, it's a problem in the simulations, not in RecoDecay.

[Luca610]

Hi @vkucera, yes this is the case. I don't know if it is an issue or a feature of simulations: these tracks degrade the resolution on the reconstructed invariant mass, so it can be usefull to tag them separately to study this effect. Anyway this changes allow to account for this effect and easily match them with RecoDecay.

[vkucera]

Thanks @Luca610 , I understand the problem now. Your solution looks fine to me. Let me just suggest some improvements in the code.

[alibuild]

Error while checking build/O2Physics/o2 for 9154ad4 at 2024-11-08 16:46:

## sw/BUILD/O2Physics-latest/log
/sw/SOURCES/O2Physics/8345-slc7_x86-64/0/Common/Core/RecoDecay.h:729:11: error: 'nPiToMuLocal' was not declared in this scope
/sw/SOURCES/O2Physics/8345-slc7_x86-64/0/Common/Core/RecoDecay.h:733:11: error: 'nKaToPiLocal' was not declared in this scope
/sw/SOURCES/O2Physics/8345-slc7_x86-64/0/Common/Core/RecoDecay.h:811:20: error: 'nPiToMuLocal' was not declared in this scope
/sw/SOURCES/O2Physics/8345-slc7_x86-64/0/Common/Core/RecoDecay.h:814:20: error: 'nKaToPiLocal' was not declared in this scope
ninja: build stopped: subcommand failed.

Full log here.