Measurement of the Charged Multiplicities in b, c and Light Quark Events from Z0 Decays

TL;DR

This paper measures charged particle multiplicities in events from Z0 decays for different quark flavors, providing data that supports QCD predictions and challenges flavor-independent fragmentation models.

Contribution

First precise measurements of charged multiplicities for b, c, and light quark events from Z0 decays, with comparison to QCD predictions and previous data.

Findings

Measured multiplicities: uds=20.21, c=21.28, b=23.14.

Differences: Δn_c=1.07, Δn_b=2.93.

Results agree with QCD and disfavor flavor-independent fragmentation.

Abstract

Average charged multiplicities have been measured separately in $b$, $c$ and light quark ($u,d,s$) events from $Z^0$ decays measured in the SLD experiment. Impact parameters of charged tracks were used to select enriched samples of $b$ and light quark events, and reconstructed charmed mesons were used to select $c$ quark events. We measured the charged multiplicities: $\bar{n}_{uds} = 20.21 \pm 0.10 (\rm{stat.})\pm 0.22(\rm{syst.})$, $\bar{n}_{c} = 21.28 \pm 0.46(\rm{stat.}) ^{+0.41}_{-0.36}(\rm{syst.})$ $\bar{n}_{b} = 23.14 \pm 0.10(\rm{stat.}) ^{+0.38}_{-0.37}(\rm{syst.})$, from which we derived the differences between the total average charged multiplicities of $c$ or $b$ quark events and light quark events: $\Delta \bar{n}_c = 1.07 \pm 0.47(\rm{stat.})^{+0.36}_{-0.30}(\rm{syst.})$ and $\Delta \bar{n}_b = 2.93 \pm 0.14(\rm{stat.})^{+0.30}_{-0.29}(\rm{syst.})$. We compared these measurements with those at lower center-of-mass energies and with perturbative QCD predictions. These combined results are in agreement with the QCD expectations and disfavor the hypothesis of flavor-independent fragmentation.