First observation of the hadronic transition $\hat{I}\yen (4S)\to \hat{I}\cdot h_b(1P)$ and new measurement of the $h_b(1P)$ and $\hat{I}{\cdot }_b(1S)$ parameters

Abstract

Using a sample of $771.6\times 10^6$ $\hat{I}\yen (4S)$ decays collected by the Belle experiment at the KEKB $e^{+}{e}^{-}$ collider, we observe for the first time the transition $\hat{I}\yen (4S)\to \hat{I}\cdot h_b(1P)$ with the branching fraction $\mathcal{B}[\hat{I}\yen (4S)\to \hat{I}\cdot h_b(1P)]=(2.18\pm 0.11\pm 0.18)\times 10^{-3}$ and we measure the $h_b(1P)$ mass $M_{h_b(1P)}=(9899.3\pm 0.4\pm 1.0)$ MeV/$c^2$, corresponding to the hyperfine splitting $\hat{I}”M_{\mathrm{H}F}(1P)=(0.6\pm 0.4\pm 1.0)$ MeV/$c^2$. Using the transition $h_b(1P)\to {\hat{I}}^3\hat{I}{\cdot }_b(1S)$, we measure the $\hat{I}{\cdot }_b(1S)$ mass $M_{\hat{I}{\cdot }_b(1S)}=(9400.7\pm 1.7\pm 1.6)$ MeV/$c^2$, corresponding to $\hat{I}”M_{\mathrm{H}F}(1S)=(59.6\pm 1.7\pm 1.6)$ MeV/$c^2$, the $\hat{I}{\cdot }_b(1S)$ width $\hat{I}{“}_{\hat{I}{\cdot }_b(1S)}=(8_{-5}^{+6}\pm 5)$ MeV/$c^2$ and the branching fraction $\mathcal{B}[h_b(1P)\to {\hat{I}}^3\hat{I}{\cdot }_b(1S)]=(56\pm 8\pm 4)\%$.

7 pages, 2 figures, submitted to Phys. Rev. Lett