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We report a search for B decays to selected final states with the ηc meson: B± → K±ηcπ+π-, B± → K±ηcω, B± → K±ηcη and B± → K±ηcπ0. The analysis is based on 772 × 106 BB-bar pairs collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. We set 90% confidence level upper limits on the branching fractions of the studied B decay modes, independent of intermediate resonances, in the range (0.6–5.3) × 10-4. We also search for molecular-state candidates in the D0D*-bar0 - D-bar0D*0, D0D-bar0 + D-bar0D0 and D*0D*-bar0 + D*-bar0D*0 combinations, neutral partners of the Z(3900)± and Z(4020)±, and a poorly understood state X(3915) as possible intermediate states in the decay chain, and set 90% confidence level upper limits on the product of branching fractions to the mentioned intermediate states and decay branching fractions of these states in the range (0.6–6.9) × 10-5.

We present a measurement of the time-dependent CP violation parameters in B0 → η'K0 decays. The measurement is based on the full data sample containing 772×106 BB-bar pairs collected at the Υ(4S) resonance using the Belle detector at the KEKB asymmetric-energy e+e- collider. The measured values of the mixing-induced and direct CP violation parameters are: sin 2φ1eff = +0.68 ± 0.07 ± 0.03, Aη'K0 = +0.03 ± 0.05 ± 0.04, where the first uncertainty is statistical and the second is systematic. The values obtained are the most accurate to date. Furthermore, these results are consistent with our previous measurements and with the world-average value of sin 2φ1 measured in B0 → J/ψK0 decays.

(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) Abstract We report a search for B decays to selected final states with the [eta] ^sub c^ meson: B ^sup ±^ [arrow right] K ^sup ±^ [eta] ^sub c^ [pi] ^sup +^ [pi] ^sup -^, B ^sup ±^ [arrow right] K ^sup ±^ [eta] ^sub c^ [omega], B ^sup ±^ [arrow right] K ^sup ±^ [eta] ^sub c^ [eta] and B ^sup ±^ [arrow right] K ^sup ±^ [eta] ^sub c^ [pi] ^sup 0^. The analysis is based on 772 × 10^sup 6^ ... pairs collected at the [Upsilon](4S) resonance with the Belle detector at the KEKB asymmetric-energy e ^sup +^ e ^sup -^ collider. We set 90% confidence level upper limits on the branching fractions of the studied B decay modes, independent of intermediate resonances, in the range (0.6-5.3) × 10^sup -4^. We also search for molecular-state candidates in the ... and ... combinations, neutral partners of the Z(3900)^sup ±^ and Z(4020)^sup ±^, and a poorly understood state X(3915) as possible intermediate states in the decay chain, and set 90% confidence level upper limits on the product of branching fractions to the mentioned intermediate states and decay branching fractions of these states in the range (0.6-6.9) × 10^sup -5^. [Figure not available: see fulltext.]

We report a high-statistics measurement of the differential cross section of the process γγ → K⁰_(S) K⁰_(S) in the range 1.05 GeV ≤ W ≤ 4.00 GeV, where W is the center-of-mass energy of the colliding photons, using 972 fb-1 of data collected with the Belle detector at the KEKB asymmetric-energy e⁺ e⁻ collider operated at and near the Υ-resonance region. The differential cross section is fitted by parameterized S-, D0-, D2-, G0- and G2-wave amplitudes. In the D2 wave, the f₂(1270), a₂(1320) and f^(′)₂(1525) are dominant and a resonance, the f₂(2200), is also present. The f₀(1710) and possibly the f₀(2500) are seen in the S wave. The mass, total width and product of the two-photon partial decay width and decay branching fraction to the KK̅ state Γᵧᵧ(ΒKK̅) are extracted for the f^(′)₂(1525), f₀(1710), f₂(2200) and f₀(2500). The destructive interference between the f₂(1270) and a₂(1320) is confirmed by measuring their relative phase. The parameters of the charmonium states Χ_(c0) and Χ_(c2) are updated. Possible contributions from the Χ_(c0)(2P) and Χ_(c2)(2P) states are discussed. A new upper limit for the branching fraction of the P- and CP-violating decay channel η_(c) → K⁰_(S) K⁰_(S) is reported. The detailed behavior of the cross section is updated and compared with QCD-based calculations.

(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) Abstract We present a measurement of the time-dependent CP violation parameters in B ^sup 0^ [arrow right] [eta]'K ^sup 0^ decays. The measurement is based on the full data sample containing 772 × 10^sup 6^ ... pairs collected at the [Upsilon](4S) resonance using the Belle detector at the KEKB asymmetric-energy e ^sup +^ e ^sup -^ collider. The measured values of the mixing-induced and direct CP violation parameters are: ... ... where the first uncertainty is statistical and the second is systematic. The values obtained are the most accurate to date. Furthermore, these results are consistent with our previous measurements and with the world-average value of sin 2 ^sub 1^ measured in B ^sup 0^ [arrow right] J/[psi]K ^sup 0^ decays. [Figure not available: see fulltext.]

We propose a new algorithm for the identification of the production flavor of neutral \\(D\\) mesons in the Belle II experiment. The algorithm exploits the correlation between the flavor of a reconstructed neutral \\(D\\) meson (signal \\(D\\) meson) and the electric charges of particles reconstructed in the rest of the \\(e^+e^-\\to c \\bar{c}\\) event. These include those originating from the decay of the other charm hadron produced in the event, as well as those possibly produced in association with the signal \\(D\\) meson. We develop the algorithm using simulation and calibrate it in data using decay modes that identify the flavor of the decaying neutral \\(D\\) meson. We use a data sample of \\(e^+e^-\\) collisions, corresponding to \\(362\\,\\mathrm{fb}^{-1}\\) of integrated luminosity, collected by Belle II at center-of-mass energies near the \\(\\Upsilon(4S)\\) mass. The effective tagging efficiency in data is \\((47.91 \\pm 0.07 \\mathrm{(stat)} \\pm 0.51 \\mathrm{(syst)})\\%\\), independent of the neutral-\\(D\\)-meson decay mode. This charm flavor tagger will approximately double the effective sample size of many \\(CP\\)-violation and charm-mixing measurements that so far have exclusively relied on neutral \\(D\\) mesons originating from \\(D^{*\\pm}\\) decays. While developed for Belle II, the basic principles underlying the charm flavor tagger can be used in other experiments, including those at hadron colliders.

We report a search for the lepton-flavor-violating decays \\(^^\\)~(\\(=e,\\)), where \\(\\) is an undetected spin-0 particle, such as an axion-like particle using \\(73610^6\\) tau lepton pairs collected by the Belle detector at the KEKB asymmetric-energy \\(e^+e^-\\) collider. We find no evidence of signal and obtain the most stringent upper limits on the branching fractions at 95\\% confidence level: \\(B(^ e^)\\) \\(<\\) \\((0.4\\)--\\(6.4)10^-4\\) and \\(B(^ ^)\\) \\(<\\) \\((0.2\\)--\\(3.5)10^-4\\) at 95\\% confidence level for an \\(\\) mass in the range \\(0.0 m_ 1.6\\)~GeV/\\(c^2\\).