Measurement of ratios of fragmentation fractions for bottom hadrons in pp¯ collisions at s=1.96 TeV

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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 $360\text{ }\text{ }{\mathrm{pb}}^{\ensuremath{-}1}$ sample of data collected with the CDF II detector in $p\overline{p}$ collisions at $\sqrt{s}=1.96\text{ }\text{ }\mathrm{TeV}$. Semileptonic decays of ${\overline{B}}^{0}$, ${B}^{\ensuremath{-}}$, and ${\overline{B}}_{s}^{0}$ mesons, as well as ${\ensuremath{\Lambda}}_{b}^{0}$ baryons, are reconstructed. For an effective bottom hadron ${p}_{T}$ threshold of $7\text{ }\text{ }\mathrm{GeV}/c$, the fragmentation fractions are measured to be ${f}_{u}/{f}_{d}=1.054\ifmmode\pm\else\textpm\fi{}0.018(\mathrm{stat}{)}_{\ensuremath{-}0.045}^{+0.025}(\mathrm{sys})\ifmmode\pm\else\textpm\fi{}0.058(\mathcal{B})$, ${f}_{s}/({f}_{u}+{f}_{d})=0.160\ifmmode\pm\else\textpm\fi{}0.005(\mathrm{stat}{)}_{\ensuremath{-}0.010}^{+0.011}(\mathrm{sys}{)}_{\ensuremath{-}0.034}^{+0.057}(\mathcal{B})$, and ${f}_{{\ensuremath{\Lambda}}_{b}}/({f}_{u}+{f}_{d})=0.281\ifmmode\pm\else\textpm\fi{}0.012(\mathrm{stat}{)}_{\ensuremath{-}0.056}^{+0.058}(\mathrm{sys}{)}_{\ensuremath{-}0.087}^{+0.128}(\mathcal{B})$, where the uncertainty $\mathcal{B}$ 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 ${f}_{{\ensuremath{\Lambda}}_{b}}/({f}_{u}+{f}_{d})$ is approximately twice the value previously measured at LEP. The approximately $2\ensuremath{\sigma}$ discrepancy is examined in terms of kinematic differences between the two production environments.

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