Bug in madspin in MG2.6.3.2

[Lailin Xu]

Hi,

I was running MG2.6.3.2. There seems to be a bug in madspin:
MadSpin/interface_madspin.py.

The line 990:
if not (particle.pdg in self.final_state or particle.pdg in evt_decayfile):

shoud be:

if (particle.pdg not in self.final_state) or (particle.pdg not in evt_decayfile):

or equivalent.

My understanding is that this line basically checks if the particles in the LHE files should decay or not. The intermediate particles (those not in self.final_state),
or particles not in the decay list (evt_decayfile) should be ignored.

Using the original MG2.6.3.2 code I got an error when running madspin:
File "/afs/cern.ch/user/r/rles/public/MG5_aMC_v2_6_3_2/MadSpin/interface_madspin.py", line 990, in run_bridge
    nb_decay = len(evt_decayfile[particle.pdg])
KeyError: 1

Apparently quarks (pdgID=1) should not decay. This problem can be fixed if I change line 990.

The correct one is actually used in the previous version of MG (like 2.4). Somehow it's changed in later versions.

Maybe you can take a look?
Thanks,
Lailin