PWGHF: fix L(1520) PDG code.

[mfaggin]

Fixing Lambda(1520) PDG code in candidateCreator3Prong.cxx, aligning it to the expected value, as done in O2DPG here: PR #1673.

Tested on 1 file of HF_LHC24g5_All MC production (see bin centered at 3 below):

[vkucera]

@mfaggin @fgrosa , I think this requires a thorough cross check between the MC numbering scheme and the ROOT numbering scheme, because these two should be identical and if they are not, it can be a big problem.

The code 3124 corresponds to the PDG numbering scheme used in the particle table of TDatabasePDG in ROOT, from where we get the particle properties.

See https://root.cern/doc/master/TPDGCode_8h.html
and grep 1520 $ROOTSYS/etc/pdg_table.txt:

  522 Lambda(1520)0      3124  1 100 Baryon      0 1.519000e+00 1.600000e-02 -100 -1 -100 -1   -1  12
  523 Lambda(1520)_bar  -3124     522     0

If particle.pdgCode() returns the MC code instead of the ROOT one, we have a problem.

[fgrosa]

Hi @vkucera indeed the pdg code for the L(1520) is an issue if one uses TDatabasePDG, because it was modified in pythia but not in ROOT (see the pdg numbering scheme from 2014 was already updated https://pdg.lbl.gov/2014/reviews/rpp2014-rev-monte-carlo-numbering.pdf). I think it would be worth to open an issue / PR in ROOT, what do you think?

[vkucera]

Hi @vkucera indeed the pdg code for the L(1520) is an issue if one uses TDatabasePDG, because it was modified in pythia but not in ROOT. I think it would be worth to open an issue / PR in ROOT, what do you think?

I agree. Can you link the change in PYTHIA here?