Quark combinatorics and meson production ratios in hadronic Z^0 decays

Rich experimental data accumulated in the past few years in the hadronic $Z^0$ decays allow one to check the quark combinatorics relations for a new type of processes, namely: quark jets in the decays $Z^0 \to q\bar q \to hadrons$. In this paper we review quark combinatorics rules for the yields of vector and pseudoscalar mesons, $V/P$, in the central and fragmentation regions of the hadronic $Z^0$ decays. It is stressed that in the central region a direct verification of quark combinatorics rules is rather problematic because of a considerable background related to the decay of highly excited resonances; however such a verification is possible in the fragmentation region, at $x_{hadron} \sim 0.5-1$, where the contribution of resonance decays is suppressed due to the rapid decrease of spectra with increasing $x_{hadron}$. It is shown that the experimental data in the fragmentation region for $\rho^0/\pi^0$ and $p/\pi^+$ are in a reasonable agreement with the predictions of quark combinatorics. The ratios of the heavy meson yields, $B^*/B$ and $D^*/D$, are also discussed: the data demonstrate a good agreement with the quark combinatorial results. We analyse the structure of the suppression parameters for strange and heavy quark productions in soft processes and estimate their order of magnitudes in the multiperipheral processes; the ratio $K^{\pm}/\pi^{\pm}$ at $x_{hadron}\sim 0.5-0.8$ and production probabilities of the $c\bar c$ and $b \bar b$ mesons are in a good agreement with the estimates.