Quark masses are not particularly well defined. In the program it is necessary to make use of three kinds of masses, kinematical, running current algebra ones and constituent ones. The first ones are relevant for the kinematics in hard processes, e.g. in , and are partly fixed by such considerations [Nor98]. The second define couplings to Higgs particles, and also other mass-related couplings in models for physics beyond the Standard Model. Both these kinds directly affect cross sections in processes. Constituent masses, finally, are used to derive the masses of hadrons, for some not yet found ones, and e.g. to gauge the remainder-mass below which the final two hadrons are to be produced in string fragmentation.
The first set of values are the ones stored in the standard mass array
PMAS. The starting values of the running masses are stored in
PARF(91) - PARF(96), with the running calculated in the PYMRUN
function. Constituent masses are also stored in the PARF array, above
position 101. We maintain this distinction for the five first
flavours, and partly for top, using the following values by default:
|quark||kinematical||current algebra mass||constituent mass|
|d||0.33 GeV||0.0099 GeV||0.325 GeV|
|u||0.33 GeV||0.0056 GeV||0.325 GeV|
|s||0.5 GeV||0.199 GeV||0.5 GeV|
|c||1.5 GeV||1.23 GeV||1.6 GeV|
|b||4.8 GeV||4.17 GeV||5.0 GeV|
|t||175 GeV||165 GeV||--|
Particle masses, when known, are taken from ref. [PDG96]. Hypothesized particles, such as fourth generation fermions and Higgs bosons, are assigned some not unreasonable set of default values, in the sense of where you want to search for them in the not-too-distant future. Here it is understood that you will go in and change the default values according to your own opinions at the beginning of a run.
The total number of hadrons in the program is very large, whereof
some are not yet discovered (like charm and bottom baryons). There
the masses are built up, when needed, from the constituent masses.
For this purpose one uses formulae of the type
|pseudoscalars and vectors||0.||0.16 GeV|
|axial vectors ()||0.50 GeV||0.|
|axial vectors ()||0.55 GeV||0.|
|baryons||0.11 GeV||0.048 GeV|
|diquarks||0.077 GeV||0.048 GeV.|