Studies of hadron spectroscopy at Belle and Belle II

Key Points

Evidence for the $h_b(2P) \to \Upsilon(1S) \eta$ transition was observed, highlighting new transitions among hadron states.
The measured branching fraction for the observed transition is lower than expected from similar decays, indicating further investigation is needed.
Searches were conducted for several decay transitions, but no evidence was found for some, such as $h_b(1P,2P) \to \Upsilon(1S) \pi^0$.
New evidence for the exotic state $P_{c\bar c s}(4459)^0 \to J/\psi \Lambda$ was found in inclusive ${\Upsilon(1S,2S)}$ decays, marking a significant discovery.

Abstract

The Belle and Belle II experiments have collected a 1. 6\, ab^-1 sample of e^+e^- collision data at center-of-mass energies near the (nS) resonances. We conduct searches for transitions from the spin-singlet hb (1P, 2P) states to the spin-triplet (1S) and ₁₉ (1P) states. We do not find evidence for the hb (1P, 2P) (1S) ⁰ and hb (2P) ₁₉ (1P) transitions. We find the first evidence for the hb (2P) (1S) transition. However, the measured branching fraction is lower than expected from related decays. Furthermore, we find evidence for P₂ ₂ ₒ (4459) ⁰ J/ decays in inclusive (1S, 2S) decays. This is the first evidence for an exotic state produced in (1S, 2S) decays.

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Studies of hadron spectroscopy at Belle and Belle II

Key Points

Abstract

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