Measurement of Ratios of Fragmentation Fractions for Bottom Hadrons in p-pbar Collisions at sqrt{s}=1.96 TeV

TL;DR

This study provides the first precise measurements of b-quark fragmentation fractions into bottom hadrons in p-pbar collisions at the Tevatron Run II, using semileptonic decays to build a five-channel lepton–charm sample. A data-driven sample-composition approach relates observed yields to parent bottom-hadron species, with MC simulations and targeted data corrections yielding relative efficiencies. The results show f_u/f_d ≈ 1.054, f_s/(f_u+f_d) ≈ 0.160, and f_{Lambda_b}/(f_u+f_d) ≈ 0.281, with f_{Lambda_b} notably higher than LEP values, suggesting possible environment- or momentum-dependent fragmentation. A momentum-binned analysis hints that f_{Lambda_b}/(f_u+fd) may decrease with increasing bottom-hadron p_T, offering insight into hadronization differences between hadron colliders and e+e− machines and guiding future fragmentation studies.

Abstract

This paper describes the first measurement of b-quark fragmentation fractions into bottom hadrons in Run II of the Tevatron Collider at Fermilab. The result is based on a 360 pb-1 sample of data collected with the CDF II detector in p-pbar collisions at sqrt{s}=1.96 TeV. Semileptonic decays of B0, B+, and B_s mesons, as well as Lambda_b baryons, are reconstructed. For an effective bottom hadron p_T threshold of 7 GeV/c, the fragmentation fractions are measured to be f_u/f_d=1.054 +/- 0.018 (stat) +0.025-0.045(sys) +/- 0.058 (Br), f_s/(f_u+f_d)=0.160 +/- 0.005 (stat) +0.011-0.010 (sys) +0.057-0.034 (Br), and f_{Lambda_b}/(f_u+f_d)=0.281\pm0.012 (stat) +0.058-0.056 (sys) +0.128-0.086 (Br), where the uncertainty (Br) is due to uncertainties on measured branching ratios. The value of f_s/(f_u+f_d) agrees within one standard deviation with previous CDF measurements and the world average of this quantity, which is dominated by LEP measurements. However, the ratio f_{Lambda_b}/(f_u+f_d) is approximately twice the value previously measured at LEP. The approximately 2 sigma discrepancy is examined in terms of kinematic differences between the two production environments.

Figures (16)

• Figure 1: Sketch of semileptonic $B$-decay topology in the transverse plane, where $V_P$ is the primary vertex, $V_B$ is the decay vertex of the bottom hadron, $V_D$ is the decay vertex of the charm hadron, and $d_0$ is defined in the text. "SVT" indicates the track selected by the displaced track SVT trigger, which is also defined in the text.
• Figure 2: Comparisons between data and simulation of $p_T(\pi_*^+)$, the soft pion from the $D^{*+}$ decay, for the (a) $\mu^-D^{*+}$ and (b) $e^-D^{*+}$ mode.
• Figure 3: E/ dx d$E/$d$x$${\cal LR}$ distribution for protons from $\Lambda^0\rightarrow p\pi^-$ and kaons and pions from $D^{*+}\rightarrow D^0\,(\rightarrow K^-\pi^+)\,\pi^+$ with the proton hypothesis applied. Tracks with ${\cal LR}$ to the right of the dashed vertical line are identified as protons.
• Figure 4: Monte Carlo simulation reflection shapes for (a) $D^0$, (b) $D^{*+}$, (c) $D^+$, (d) $D^+_s$, and (e) $\Lambda_c^+$. The shapes are normalized to their expected contributions, assuming $f_u:f_d:f_s:f_{\Lambda_b}=0.4:0.4:0.1:0.1$, used for illustrative purposes only.
• Figure 5: Combined $D^+_s e^-$ and $D^+_s\mu^-$ reflection into the $K^+\pi^-\pi^-$ invariant mass. The reflection is determined from an inclusive MC sample of $\bar{B}_s^0\rightarrow\ell^-\bar{\nu}_{\ell}D^+_s X$, where all $D^+_s$ meson decay modes are included.