Measurement of the b-quark fragmentation function in Z0 decays

TL;DR

This work presents a precision measurement of the inclusive b-quark fragmentation function D(x_B) in Z0 decays using a novel inclusive B-hadron energy reconstruction based on topological vertexing. By reconstructing B-hadron energies with high efficiency and resolution across the full kinematic range, the authors unfold the true D(x_B) distribution from detector effects and confront it with a suite of fragmentation formalisms and functional forms. The analysis identifies which parameterizations describe the data (notably Bowler, Lund, Kartvelishvili, and UCLA within JETSET) while excluding several commonly used forms (e.g., Peterson, BCFY, CS) and certain HERWIG settings, achieving a final mean scaled energy <x_B> = 0.709 with small, well-quantified uncertainties. The resulting D(x_B) distribution exhibits reduced model dependence compared with prior measurements and provides stringent inputs for heavy-quark fragmentation modeling at the Z0 energy scale.

Abstract

We present a measurement of the b-quark inclusive fragmentation function in Z0 decays using a novel kinematic B-hadron energy reconstruction technique. The measurement was performed using 350,000 hadronic Z0 events recorded in the SLD experiment at SLAC between 1997 and 1998. We compared the sacled B-hadron energy distribution with models of b-quark fragmentation and with several ad hoc functional forms. A number of models and functions are excluded by the data. The average scaled energy of weakly-decaying B hadrons was measured to be <x_B>= 0.709 +-0.003 (stat) +-0.003 (syst) +-0.002 (model).

Figures (11)

• Figure 1: Distribution of the reconstructed $P_{t}$-corrected vertex mass (points). The simulated distribution is also shown (histogram) in which the flavor composition is indicated: $b$ (open), $c$ (cross hatched), and $uds$ (dark shaded).
• Figure 2: The relative deviation of the maximum missing mass from the true missing mass for simulated $B$ hadron decays; the contributions from different $B$ species are indicated separately: $B^{0}$ and $B^{\pm}$ (open), $B_{s}^{0}$ (cross-hatched), and $\Lambda_{b}$ (dark shaded).
• Figure 3: Distribution of the reconstructed $M_{0max}^{2}$ for the selected vertices (points). The simulated distribution is also shown (histogram) in which the flavor composition is indicated: $b$ (open), $c$ (cross hatched), and $uds$ (dark shaded).
• Figure 4: Distribution of the reconstructed $M_{0max}^{2}$ for the final selected sample (see text). The simulated distribution is also shown (histogram) in which the flavor composition is indicated: $b$ (open), $c$ (cross hatched), and $uds$ (dark shaded).
• Figure 5: The simulated efficiency for selecting $B$ hadrons as a function of the true scaled $B$-hadron energy, $x_B^{true}$.