Charm Hadrons from Fragmentation and B decays in e+e- Annihilation at $\sqrt{s}=$10.6 GeV

TL;DR

The study delivers a precision measurement of charm-quark fragmentation at sqrt(s) ≈ 10.58 GeV with Belle, extracting x_P spectra and moments for D^0, D^+, D_s^+, Λ_c^+, and D^{*} states, and quantifying production in B decays and angular distributions. It employs extensive MC-based efficiency corrections and a reweighting approach to compare against multiple fragmentation-function models, finding Bowler and Lund fragmentation provide the best description while Peterson performs poorly. The results include total production cross-sections, feed-down assessments from higher resonances, and a comprehensive set of ratios that test MC predictions, offering valuable input for tuning hadronization models in heavy-quark fragmentation at low energies. These measurements advance the understanding of nonperturbative QCD hadronization and supply concrete data for MC tuning and fragmentation theory.

Abstract

We present an analysis of charm quark fragmentation at 10.6 GeV, based on a data sample of 103 fb collected by the Belle detector at the KEKB accelerator. We consider fragmentation into the main charmed hadron ground states, namely \DZ, \DP, \Ds and \LC, as well as the excited states \DSZ and \DSP. The fragmentation functions are important to measure as they describe processes at a low energy scale, where calculations in perturbation theory lead to large uncertainties. Fragmentation functions can also be used as input distributions for Monte Carlo generators. Additionally, we determine the average number of these charmed hadrons produced per B decay at the \Ys resonance and measure the distribution of their production angle in \epem annihilation events and in B decays.

Figures (11)

• Figure 1: Mass and mass difference distributions for all charmed hadrons reconstructed in this analysis, for $0.28 < \mathrm{x_P} < 0.30$ for the continuum sample. The histograms show the data, the dotted line describes only the background, the full line includes the signal. The top row shows the $D^0$ (left) and the $D^+$ (right), the middle shows the $D^+_s$ (left) and the $\Lambda^+_c$ (right), and the bottom row shows $D^{*+}\to D^0\pi^+$ (left), the alternative decay mode $D^{*+}\to D^+\pi^0$ (middle), and the $D^{*0}$ (right).
• Figure 2: Mass and mass difference distributions for all charmed hadrons reconstructed in this analysis, for $0.68<\mathrm{x_P}<0.70$. The order of the plots is the same as in Fig. \ref{['mass-xp-fita']}. As in the previous figure, the histograms show the data, the dotted lines describe only the background, the full lines include the signal.
• Figure 3: The signal yield not corrected for efficiencies for the charmed hadrons. The order of the particles is the same as in Fig. \ref{['mass-xp-fita']}. The contribution from $B$ decays in the on-resonance samples (down-left hatching) is clearly visible in the region $\mathrm{x_P}<0.5$. The error bars show the statistical uncertainties only.
• Figure 4: The efficiencies for the charmed hadrons used in this analysis. The order of the particles is the same as in Fig. \ref{['mass-xp-fita']}. The different production angle distributions for the on-resonance (down-left hatching) and the continuum sample (down-right hatching) result in different efficiencies for these samples. The error bars show the statistical uncertainties only.
• Figure 5: Efficiency corrected momentum distributions for the charmed hadrons produced in $e^+e^-$-annihilation events, i.e. from fragmentation of charm quarks. The order of the particles is the same as in Fig. \ref{['mass-xp-fita']}. For $\mathrm{x_P}>0.5$, the on-resonance and continuum data have been combined by a weighted average. The inner error bars show the statistical, the outer error bars the total uncertainties.