Pseudoscalar- meson masses in a quark model

Psuedoscalar-meson masses and sum rules are compared in two different limit of a quark model with 4 quarks. The conventional limit corresponds to a heavy cc state and generalises ideal mixing in a nonet. The second limit corresponds to a missing US4 unitary singlet and appears more relevant to be masses of π, K, eta, eta'. If SU3 is broken only by the mass difference between the strange and nonstrange quarks, the physical masses imply that the uu, dd and ss pairs account only for 33% of the composition of the eta'(960), while the eta(548) this fraction is 86%. If some of the remaining matter is in the form of the constituents of J/psi, the relative proportion of the radiative decays J/psi→eta'γ vs. J/psi→etaγ is accounted for in satisfactory agreement with experiment