Production of pi+, pi-, K+, K-, p and p-bar in Light (uds), c and b Jets from Z0 Decays

TL;DR

This study provides precise, flavor-separated measurements of hadron production in Z0 decays using the SLD detector, including identified π±, K±, and p/ p-bar across a wide momentum range. By exploiting vertexing and CRID-based particle identification, the authors separate light (uds), c, and b jets and compare the data to MLLA+LPHD predictions and three hadronization models (JETSET, UCLA, HERWIG). The results reveal pronounced flavor dependencies and leading-particle effects, offering stringent tests and clear deficiencies in current hadronization models, especially for heavy-flavor jets. Overall, the work strengthens our understanding of fragmentation dynamics and provides robust constraints for tuning hadronization models in high-energy processes.

Abstract

We present improved measurements of the differential production rates of stable charged particles in hadronic Z0 decays, and of charged pions, kaons and protons identified over a wide momentum range using the SLD Cherenkov Ring Imaging Detector. In addition to flavor-inclusive Z0 decays, measurements are made for Z0 decays into light (u, d, s), c and b primary flavors, selected using the upgraded Vertex Detector. Large differences between the flavors are observed that are qualitatively consistent with expectations based upon previously measured production and decay properties of heavy hadrons. These results are used to test the predictions of QCD in the Modified Leading Logarithm Approximation, with the ansatz of Local Parton-Hadron Duality, and the predictions of three models of the hadronization process. The light-flavor results provide improved tests of these predictions, as they do not include the contribution of heavy-hadron production and decay; the heavy-flavor results provide complementary model tests. In addition we have compared hadron and antihadron production in light quark (as opposed to antiquark) jets. Differences are observed at high momentum for all three charged hadron species, providing direct probes of leading particle effects, and stringent constraints on models.

Figures (14)

• Figure 1: a) Charged track $x_p$ distribution in hadronic events (dots) with logarithmic and (inset) linear vertical scales, compared with the predictions of three models (lines). b) The same data divided by the JETSET prediction. The error bars in (b) are statistical and the shaded band represents the systematic uncertainty; all errors except an overall 1% normalization uncertainty are included in (a).
• Figure 2: Calibrated identification efficiencies for selected tracks. The half-widths of the grey bands represent the systematic uncertainties, which are strongly correlated between momenta. The off-diagonal efficiencies have been scaled by factors of five for clarity. The white bands in the four upper left plots represent the 2$\times$2 matrix used below kaon threshold in the liquid system.
• Figure 3: a) Measured charged hadron production fractions in hadronic $Z^0$ decays. The circles represent the $\pi^\pm$ fraction, the squares the $K^\pm$ fraction, the diamonds the p/$\bar{\rm p}$ fraction. The error bars are statistical only; the shaded areas indicate the systematic errors, and are connected across momentum regions where there is a strong positive correlation. b) The sum of the three fractions.
• Figure 4: Comparison of our measured charged hadron fractions (symbols) with the predictions of the JETSET (dashed lines), UCLA (solid lines) and HERWIG (dotted lines) models.
• Figure 5: Comparison of our measured (a) charged particle and pion and (b) kaon and proton production rates (symbols) with the predictions of the JETSET (dashed lines), UCLA (solid lines) and HERWIG (dotted lines) models.