PYTHIA 6 Translation Table

For those more familiar with PYTHIA 6 than PYTHIA 8, here comes a table that shows the approximate correspondence between some commonly used variables in the two programs.The list can be expanded to meet explicit needs (channel your suggestions via the Monte Carlo responsible of your collaboration), but there is no question of ever providing anywhere near a complete coverage.

Selecting properties of event generation

For PYTHIA 8 you should use the pythia->readString("command") to give in the commands listed below, assuming that you have access to a pointer pythia to an instance of the Pythia class.
PYTHIA 6 PYTHIA 8 Comment
MSEL = 1 SoftQCD:minBias = on soft and hard QCD events (for pp/pbarp)
MSEL = 2 SoftQCD:all = on as above, plus elastic and diffractive (for pp/pbarp)
MSTP(61) = 0 PartonLevel:ISR = off no initial-state radiation
MSTP(71) = 0 PartonLevel:FSR = off no final-state radiation
MSTP(81) = 0 PartonLevel:MI = off no multiple parton-parton interactions
MSTP(111) = 0 HadronLevel:all = off no hadronization and no decays

Information about generated event

Several PYTHIA 6 variables are stored in two places, and then both are given below. For PYTHIA 8 it is assumed that you have access to a pointer pythia to an instance of the Pythia class.
PYTHIA 6 PYTHIA 8 Comment
msti(1), mint(1) pythia->info.code() process ID (but changed numbering)
pari(13), vint(43) pythia->info.mHat() invariant mass of the hard subprocess
pari(17), vint(47) pythia->info.pTHat() transverse momentum of the hard subprocess (2 -> 2)
pari(21), vint(51) pythia->info.QRen() renormalization scale Q of the hard subprocess (default definition changed)
vint(57) pythia->info.alphaEM() electromagnetic coupling constant in the hard subprocess
vint(58) pythia->info.alphaS() strong coupling constant in the hard subprocess
msti(15), mint(15) pythia->info.id1() ID of the first incoming parton
msti(16), mint(16) pythia->info.id2() ID of the second incoming parton
pari(33), vint(41) pythia->info.x1() momentum fraction x of the first incoming parton
pari(34), vint(42) pythia->info.x2() momentum fraction x of the second incoming parton
pari(23), vint(53) pythia->info.QFac() factorization scale Q of the hard subprocess (default definition changed)
pari(29), vint(39) pythia->info.pdf1() x1*f(x1) (PDF density 1)
pari(30), vint(40) pythia->info.pdf2() x2*f(x2) (PDF density 2)
pari(7), vint(97) pythia->info.weight() event weight (normally unity)