Primary vertex multiplicity
Pythia 6 has a substantially higher average primary vertex multiplicity than Pythia 5.
Pythia 6 can be tuned to be a good match to the data except for the PK? where it is very low and for KK? where it is slightly high
The primary vertex multiplicity depends on the assumed Q/DQ split which also has a major influence on the charm-anticharm asymmetry.
Note that states with especially high primary vertex multiplicities are K? , K3? , and PK?. This could reflect the fact that K? , K3? can be parts of D*. Perhaps the PK? is often from ?* which aren’t simulated presently.