The conjecture that particle masses are multiples of a unit u of about 35 MeV has been proposed in various forms by several authors: mesons are even multiples of u, leptons and baryons odd multiples. Here this mass quantization is reassessed for all particles with mass below 1 GeV (stable leptons and f0(600) excluded),
and found to be statistically significant. Subsequently all the mesons listed by the PDG are grouped in families defined by quark composition and J^PC, and analyzed for even mass multiplicity with a unit close to 35 MeV separately for each group. For all the families that can be analyzed unambiguously this multiplicity hypothesis is found to be statistically significant.
Most scalar and vector families show a dependence of u from the spin,
while for pseudoscalars the effect is not present.
Only 5 states out of 120 are rejected due to abnormally large fit residuals.
The mass units of the various families are quantized on a grid of 12 intervals of about 0.25 MeV,
ranging from 33.88 up to 36.86 MeV. The location of the values on the u-grid shows an intriguing pattern
of correlation with the quantum numbers.
12.40.Yx Hadron mass models and calculations