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

Abstract

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 → qq → 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 ∼ 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 ρ 0 /π 0 and p/π + 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 ± /π ± at x hadron ∼ 0.5 − 0.8 and production probabilities of the cc and bb mesons are in a good agreement with the estimates.

Comparing fragmentation of strange quark in Z0 decays and K+p reactions

“…For usually accepted value λ ≈ 0.3, this prediction is a factor of more than two higher than the experimental values at large x p . It deviates from the DELPHI value of 0.14 ± 0.02 at x p = 0.85 by 7 standard deviations or even more for λ ≈ 0.5 suggested in [5].…”

“…Recently Anisovich et al [5] compared these predictions with the LEP data. They analyzed the V /P ratios obtained from the ALEPH data [6] at large x p = p/p beam → 1, where a contribution of the resonance decays is supposed to be strongly suppressed, and concluded that the experimental results are consistent with V /P = 3.…”

“…The quark-combinatorics prediction, ρ 0 /(3π) = 1, is not consistent with the data, contrary to conclusion of ref. [5] based on the same analysis of the ALEPH data. It is again a factor of 2 to 5 higher than the experimental values at large x p .…”

“…On the other hand, and contrary to conclusion of ref. [5] based on the same analysis of the ALEPH data, the quark-combinatorics prediction, K * (892)/(3K) = 1, for the promptly produced mesons is ruled out by the LEP, Mirabelle and BEBC data. The experimental values at the largest x p are a factor of 3 lower than the prediction and deviate from it by at least 11 standard deviations.…”

“…The JETSET and Pei model predictions are somewhat lower than the experimental data at large x p , but consistent with them within onetwo errors. The quark-combinatorics model [4,5] predicts φ/(3K) = λ, where λ is the strangeness suppression parameter. For usually accepted value λ ≈ 0.3, this prediction is a factor of more than two higher than the experimental values at large x p .…”