We study the processes $e^{+}e^{–} → ωχ_{bJ}$(1P) (J=0, 1, or 2) using samples at center-of-mass energies $\sqrt{s}$ = 10.701, 10.745, and 10.805 GeV, corresponding to 1.6, 9.8, and 4.7 fb–1 of ...integrated luminosity, respectively. These data were collected with the Belle II detector during special operations of the SuperKEKB collider above the Υ(4S) resonance. We report the first observation of $ωχ_{bJ}$(1P) signals at $\sqrt{s}$ = 10.745 GeV. By combining Belle II data with Belle results at $\sqrt{s}$ = 10.867 GeV, we find energy dependencies of the Born cross sections for $e^{+}e^{–} → ωχ_{b1,b2}$(1P) to be consistent with the shape of the Υ(10753) state. These data indicate that the internal structures of the Υ(10753) and Υ(10860) states may differ. Including data at $\sqrt{s}$ = 10.653 GeV, we also search for the bottomonium equivalent of the X(3872) state decaying into ωΥ(1S). No significant signal is observed for masses between 10.45 and 10.65 GeV/c2.
We present the results of the first Dalitz plot analysis of the decay D 0 → K-π +η. The analysis is performed on a data set corresponding to an integrated luminosity of 953 fb-1 collected by the ...Belle detector at the asymmetric-energy e+e- KEKB collider. The Dalitz plot is well described by a combination of the six resonant decay channels K- * (892)0 η, K-a0(980)+, K-a2(1320)+, K¯ * (1410)0 η, K* (1680)-π + and K* 2 (1980)-π +, together with Kπ and Kη S-wave components. The decays K* (1680)- → K-η and K* 2 (1980)- → K-η are observed for the first time. We measure ratio of the branching fractions, B(D0→K-π+η) B(D0→K=π+) = 0.500 ± 0.002(stat) ± 0.020(syst) ± 0.003(BPDG). Using the Dalitz fit result, the ratio B(K*(1680)→Kη) B(K*(1680)→Kπ) is measured to be 0.11±0.02(stat)+0.06 =0.04(syst)± 0.04(BPDG); this is much lower than the theoretical expectations (≈ 1) made under the assumption that K* (1680) is a pure 1 3D1 state. The product branching fraction B(D 0 → K* 2 (1980)- → K-ηπ +) = (2.2 +1.7 -1.9 ) × 10-4 is determined. In addition, the πη' contribution to the a0(980)± resonance shape is confirmed with 10.1σ statistical significance using the three-channel Flatté model. We also measure B(D 0 → K¯ * (892)0 η) = (1.41+0.13 -0.12)%. This is consistent with, and more precise than, the current world average (1.02 ± 0.30)%, deviates with a significance of more than 3σ from the theoretical predictions of (0.51-0.92)%.
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