Production of π+, K+, K0, K*0, φ, p and Λ0 in hadronic Z0 decays

TLDR: In this article, the authors measured the differential production cross sections as a function of scaled momentum of the identified hadron species and the corresponding antihadron species in light quark (as opposed to antiquark) jets.

Abstract: We have measured the differential production cross sections as a function of scaled momentum ${x}_{p}{=2p/E}_{\mathrm{c}.\mathrm{m}.}$ of the identified hadron species ${\ensuremath{\pi}}^{+},$ ${K}^{+},$ ${K}^{0},$ ${K}^{*0},$ $\ensuremath{\varphi}, p$, ${\ensuremath{\Lambda}}^{0},$ and of the corresponding antihadron species in inclusive hadronic ${Z}^{0}$ decays, as well as separately for ${Z}^{0}$ decays into light $(u,$ $d,$ $s),$ c and b flavors. Clear flavor dependences are observed, consistent with expectations based upon previously measured production and decay properties of heavy hadrons. These results were used to test the QCD predictions of Gribov and Lipatov, the predictions of QCD in the modified leading logarithm approximation with the ansatz of local parton-hadron duality, and the predictions of three fragmentation models. The ratios of production of different hadron species were also measured as a function of ${x}_{p}$ and were used to study the suppression of strange meson, strange and non-strange baryon, and vector meson production in the jet fragmentation process. The light-flavor results provide improved tests of the above predictions, as they remove the contribution of heavy hadron production and decay from that of the rest of the fragmentation process. In addition we have compared hadron and antihadron production as a function of ${x}_{p}$ in light quark (as opposed to antiquark) jets. Differences are observed at high ${x}_{p},$ providing direct evidence that higher-momentum hadrons are more likely to contain a primary quark or antiquark. The differences for pseudoscalar and vector kaons provide new measurements of strangeness suppression for high-${x}_{p}$ fragmentation products.

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FIG. 3. Calibrated identification efficiencies for tracks used in the charged hadron fractions analysis. The half-widths of the gre represent the systematic uncertainties, which are strongly correlated between momenta. Note the expanded vertical scale for the o efficiencies.

TABLE IV. Proton fraction and differential cross section per hadronicZ0 decay.

FIG. 16. Ratios of production of each hadron species inb-flavor events to that in light-flavor events~left! and inc-flavor:light-flavor events~right!. Also shown are the predictions of the three fragme tation models; for each model, the predictions forK6 and K0/K̄0 were averaged, as were those forp/ p̄ andL0/L̄0. The model predictions forf are not shown, but have the samexp dependence as the corresponding prediction forK* 0/K̄* 0, with a peak value typically higher by 40%.

FIG. 15. Identified hadron differential cross sections in lig flavor events. Also shown are the predictions of the three fragm tation models; the prediction of each model forK6 is similar to that for K0/K̄0, and the two have been averaged.

FIG. 21. Normalized differences between hadron and antihad production in light quark jets. The thin dot-dashed lines in~c! and ~d! represent the fit to the baryon data scaled by the dilution fa of 0.27 described in the text. Also shown are the predictions of three fragmentation models.

FIG. 22. Ratios of measured differential cross sections for v ous pairs of hadron species in light-flavor events, along with predictions of the three fragmentation models. In all cases charge-conjugate states are included in both numerator and den nator. Here, ‘‘K’’ denotes the average ofK0/K̄0 and K6. The JETSET predictions for theK* :p1, f:p1, f:K* and K* :K ratios have been scaled by factors of 2/3, 1/2, 4/3 and 2/3, respecti ~see text!, in order to clarify the comparison of the momentu dependence.