Studies of hadron spectroscopy at Belle and Belle II

Abstract

The Belle and Belle II experiments have collected a $1.6{\mathrm{ab}}^{-1}$ sample of $e^{+}{e}^{-}$ collision data at center-of-mass energies near the $\hat{I}\yen (nS)$ resonances. We conduct searches for transitions from the spin-singlet $h_b(1P,2P)$ states to the spin-triplet $\hat{I}\yen (1S)$ and $\ddot{I}{‡}_{bJ}(1P)$ states. We do not find evidence for the $h_b(1P,2P)\to \hat{I}\yen (1S)\ddot{I}{€}^0$ and $h_b(2P)\to \ddot{I}{‡}_{bJ}(1P){\hat{I}}^3$ transitions. We find the first evidence for the $h_b(2P)\to \hat{I}\yen (1S)\hat{I}\cdot$ transition. However, the measured branching fraction is lower than expected from related decays. Furthermore, we find evidence for $P_{c\bar{c}s}(4459{)}^0\to J/\ddot{I}ˆ\hat{I}›$ decays in inclusive $\hat{I}\yen (1S,2S)$ decays. This is the first evidence for an exotic state produced in $\hat{I}\yen (1S,2S)$ decays.