Search for B

We report the results of a search for the rare, purely leptonic decay B^{-}→µ^{-}ν[over ¯]_{µ} performed with a 711 fb^{-1} data sample that contains 772×10^{6} BB[over ¯] pairs, collected near the ϒ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e^{+}e^{-} collider. The signal events are selected based on the presence of a high momentum muon and the topology of the rest of the event showing properties of a generic B-meson decay, as well as the missing energy and momentum being consistent with the hypothesis of a neutrino from the signal decay. We find a 2.4 standard deviation excess above background including systematic uncertainties, which corresponds to a branching fraction of B(B^{-}→µ^{-}ν[over ¯]_{µ})=(6.46±2.22±1.60)×10^{-7} or a frequentist 90% confidence level interval on the B^{-}→µ^{-}ν[over ¯]_{µ} branching fraction of [2.9,10.7]×10^{-7}.

Search for CP Violation and Measurement of the Branching Fraction in the Decay D

We report a study of the decay D^{0}→K_{S}^{0}K_{S}^{0} using 921 fb^{-1} of data collected at or near the ϒ(4S) and ϒ(5S) resonances with the Belle detector at the KEKB asymmetric energy e^{+}e^{-} collider. The measured time-integrated CP asymmetry is A_{CP}(D^{0}→K_{S}^{0}K_{S}^{0})=(-0.02±1.53±0.02±0.17)%, and the branching fraction is B(D^{0}→K_{S}^{0}K_{S}^{0})=(1.321±0.023±0.036±0.044)×10^{-4}, where the first uncertainty is statistical, the second is systematic, and the third is due to the normalization mode (D^{0}→K_{S}^{0}π^{0}). These results are significantly more precise than previous measurements available for this mode. The A_{CP} measurement is consistent with the standard model expectation.

Measurement of the τ Lepton Polarization and R(D

We report the first measurement of the τ lepton polarization P_{τ}(D^{*}) in the decay B[over ¯]→D^{*}τ^{-}ν[over ¯]_{τ} as well as a new measurement of the ratio of the branching fractions R(D^{*})=B(B[over ¯]→D^{*}τ^{-}ν[over ¯]_{τ})/B(B[over ¯]→D^{*}ℓ^{-}ν[over ¯]_{ℓ}), where ℓ^{-} denotes an electron or a muon, and the τ is reconstructed in the modes τ^{-}→π^{-}ν_{τ} and τ^{-}→ρ^{-}ν_{τ}. We use the full data sample of 772×10^{6} BB[over ¯] pairs recorded with the Belle detector at the KEKB electron-positron collider. Our results, P_{τ}(D^{*})=-0.38±0.51(stat)_{-0.16}^{+0.21}(syst) and R(D^{*})=0.270±0.035(stat)_{-0.025}^{+0.028}(syst), are consistent with the theoretical predictions of the standard model.

Lepton-Flavor-Dependent Angular Analysis of B→K

We present a measurement of angular observables and a test of lepton flavor universality in the B→K^{*}ℓ^{+}ℓ^{-} decay, where ℓ is either e or µ. The analysis is performed on a data sample corresponding to an integrated luminosity of 711 fb^{-1} containing 772×10^{6} BB[over ¯] pairs, collected at the ϒ(4S) resonance with the Belle detector at the asymmetric-energy e^{+}e^{-} collider KEKB. The result is consistent with standard model (SM) expectations, where the largest discrepancy from a SM prediction is observed in the muon modes with a local significance of 2.6σ.

First Observation of the Doubly Cabibbo-Suppressed Decay of a Charmed Baryon: Λ_{c}

We report the first observation of the decay Λ_{c}^{+}→pK^{+}π^{-} using a 980 fb^{-1} data sample collected by the Belle detector at the KEKB asymmetric-energy e^{+}e^{-} collider. This is the first observation of a doubly Cabibbo-suppressed decay of a charmed baryon. We measure the branching ratio of this decay with respect to its Cabibbo-favored counterpart to be B(Λ_{c}^{+}→pK^{+}π^{-})/B(Λ_{c}^{+}→pK^{-}π^{+})=(2.35±0.27±0.21)×10^{-3}, where the uncertainties are statistical and systematic, respectively.

Observation of the Decay B_{s}

We measure the decay B_{s}^{0}→K^{0}K[over ¯]^{0} using data collected at the ϒ(5S) resonance with the Belle detector at the KEKB e^{+}e^{-} collider. The data sample used corresponds to an integrated luminosity of 121.4 fb^{-1}. We measure a branching fraction B(B_{s}^{0}→K^{0}K[over ¯]^{0})=[19.6_{-5.1}^{+5.8}(stat)±1.0(syst)±2.0(N_{B_{s}^{0}B[over ¯]_{s}^{0}})]×10^{-6} with a significance of 5.1 standard deviations. This measurement constitutes the first observation of this decay.

Energy Scan of the e

Using data collected with the Belle detector at the KEKB asymmetric-energy e^{+}e^{-} collider, we measure the energy dependence of the e^{+}e^{-}→h_{b}(nP)π^{+}π^{-} (n=1, 2) cross sections from thresholds up to 11.02 GeV. We find clear ϒ(10860) and ϒ(11020) peaks with little or no continuum contribution. We study the resonant substructure of the ϒ(11020)→h_{b}(nP)π^{+}π^{-} transitions and find evidence that they proceed entirely via the intermediate isovector states Z_{b}(10610) and Z_{b}(10650). The relative fraction of these states is loosely constrained by the current data: The hypothesis that only Z_{b}(10610) is produced is excluded at the level of 3.3 standard deviations, while the hypothesis that only Z_{b}(10650) is produced is not excluded at a significant level.

Observation of B

We report the first observation of the decays B^{0}→pΛ[over ¯]D^{(*)-}. The data sample of 711 fb^{-1} used in this analysis corresponds to 772×10^{6} BB[over ¯] pairs, collected at the ϒ(4S) resonance by the Belle detector at the KEKB asymmetric-energy e^{+}e^{-} collider. We observe 19.8σ and 10.8σ excesses of events for the two decay modes and measure the branching fractions of B^{0}→pΛ[over ¯]D^{-} and B^{0}→pΛ[over ¯]D^{*-} to be (25.1±2.6±3.5)×10^{-6} and (33.6±6.3±4.4)×10^{-6}, respectively, where the first uncertainties are statistical and the second are systematic. These results are not compatible with the predictions based on the generalized factorization approach. In addition, a threshold enhancement in the dibaryon (pΛ[over ¯]) system is observed, consistent with that observed in similar B decays.

First Observation of the Hadronic Transition ϒ(4S)→ηh(b)(1P) and New Measurement of the h(b)(1P) and η(b)(1S) Parameters.

Using a sample of 771.6×10(6) ϒϒ(4S) decays collected by the Belle experiment at the KEKB e(+)e(-) collider, we observe, for the first time, the transition ϒ(4S)→ηh(b)(1P) with the branching fraction B[ϒ(4S)→ηh(b)(1P)]=(2.18±0.11±0.18)×10(-3) and we measure the h(b)(1P) mass M(h(b)(1P))=(9899.3±0.4±1.0) MeV/c(2), corresponding to the hyperfine (HF) splitting ΔM(HF)(1P)=(0.6±0.4±1.0) MeV/c(2). Using the transition h(b)(1P)→γη(b)(1S), we measure the η(b)(1S) mass M(η(b)(1S))=(9400.7±1.7±1.6) MeV/c(2), corresponding to ΔM(HF)(1S)=(59.6±1.7±1.6) MeV/c(2), the η(b)(1S) width Γ(η(b)(1S))=(8(-5)(+6)±5) MeV/c(2) and the branching fraction B[h(b)(1P)→γη(b)(1S)]=(56±8±4)%.

First Observation of CP Violation in B[over ¯]

We report a measurement of the time-dependent CP asymmetry of B[over ¯]^{0}→D_{CP}^{(*)}h^{0} decays, where the light neutral hadron h^{0} is a π^{0}, η, or ω meson, and the neutral D meson is reconstructed in the CP eigenstates K^{+}K^{-}, K_{S}^{0}π^{0}, or K_{S}^{0}ω. The measurement is performed combining the final data samples collected at the ϒ(4S) resonance by the BABAR and Belle experiments at the asymmetric-energy B factories PEP-II at SLAC and KEKB at KEK, respectively. The data samples contain (471±3)×10^{6} BB[over ¯] pairs recorded by the BABAR detector and (772±11)×10^{6} BB[over ¯] pairs recorded by the Belle detector. We measure the CP asymmetry parameters -η_{f}S=+0.66±0.10(stat)±0.06(syst) and C=-0.02±0.07(stat)±0.03(syst). These results correspond to the first observation of CP violation in B[over ¯]^{0}→D_{CP}^{(*)}h^{0} decays. The hypothesis of no mixing-induced CP violation is excluded in these decays at the level of 5.4 standard deviations.

Measurement of the Direct CP Asymmetry in B¯â†’X(s+dγ) Decays with a Lepton Tag.

We report the measurement of the direct CP asymmetry in the radiative B¯â†’X(s+dγ) decay using a data sample of (772 ± 11)×10(6) BB[over ¯] pairs collected at the ϒ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider. The CP asymmetry is measured as a function of the photon energy threshold. For Eγ*≥2.1 GeV, where Eγ* is the photon energy in the center-of-mass frame, we obtain A(CP)(B¯â†’X(s+dγ))=(2.2±3.9±0.9)%, consistent with the standard model prediction.

Difference in direct charge-parity violation between charged and neutral B meson decays.

Equal amounts of matter and antimatter are predicted to have been produced in the Big Bang, but our observable Universe is clearly matter-dominated. One of the prerequisites for understanding this elimination of antimatter is the nonconservation of charge-parity (CP) symmetry. So far, two types of CP violation have been observed in the neutral K meson (K(0)) and B meson (B(0)) systems: CP violation involving the mixing between K(0) and its antiparticle (and likewise for B(0) and ), and direct CP violation in the decay of each meson. The observed effects for both types of CP violation are substantially larger for the B(0) meson system. However, they are still consistent with the standard model of particle physics, which has a unique source of CP violation that is known to be too small to account for the matter-dominated Universe. Here we report that the direct CP violation in charged B(+/-)-->K(+/-)pi(0) decay is different from that in the neutral B(0) counterpart. The direct CP-violating decay rate asymmetry, (that is, the difference between the number of observed B(-)-->K(-)pi(0) event versus B(+)-->K(+) pi(0) events, normalized to the sum of these events) is measured to be about +7%, with an uncertainty that is reduced by a factor of 1.7 from a previous measurement. However, the asymmetry for versus B(0)-->K(+)pi(-) is at the -10% level. Although it is susceptible to strong interaction effects that need further clarification, this large deviation in direct CP violation between charged and neutral B meson decays could be an indication of new sources of CP violation-which would help to explain the dominance of matter in the Universe.

First observation of the P-wave spin-singlet bottomonium states hb(1P) and hb(2P).

We report the first observations of the spin-singlet bottomonium states h(b)(1P) and h(b)(2P). The states are produced in the reaction e(+)e(-)→h(b)(nP)π(+)π(-) using a 121.4 fb(-1) data sample collected at energies near the Υ(5S) resonance with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider. We determine M[h(b)(1P)]=(9898.2(-1.0-1.1)(+1.1+1.0)) MeV/c(2) and M[h(b)(2P)]=(10,259.8±0.6(-1.0)(+1.4)) MeV/c(2), which correspond to P-wave hyperfine splittings ΔM(HF)=(+1.7±1.5) and (+0.5(-1.2)(+1.6)) MeV/c(2), respectively. The significances of the h(b)(1P) and h(b)(2P) are 5.5σ and 11.2σ, respectively. We find that the production of the h(b)(1P) and h(b)(2P) is not suppressed relative to the production of the Υ(1S), Υ(2S), and Υ(3S).

Observation of two charged bottomoniumlike resonances in Υ(5S) decays.

We report the observation of two narrow structures in the mass spectra of the π(±)Υ(nS) (n=1, 2, 3) and π(±)h(b)(mP) (m=1, 2) pairs that are produced in association with a single charged pion in Υ(5S) decays. The measured masses and widths of the two structures averaged over the five final states are M(1)=(10,607.2±2.0) MeV/c2, Γ(1)=(18.4±2.4) MeV, and M(2)=(10,652.2±1.5) MeV/c2, Γ(2)=(11.5±2.2) MeV. The results are obtained with a 121.4 fb(-1) data sample collected with the Belle detector in the vicinity of the Υ(5S) resonance at the KEKB asymmetric-energy e+ e- collider.

Search for CP violation in the decays D(0)→K(S)(0)P(0).

We have searched for CP violation in the decays D(0)→K(S)(0)P(0) where P(0) denotes a neutral pseudoscalar meson that is either a π(0), η, or η' using KEKB asymmetric-energy e(+)e(-) collision data corresponding to an integrated luminosity of 791 fb(-1) collected with the Belle detector. No evidence of significant CP violation is observed. We report the most precise CP asymmetry measurement in the decay D(0)→K(S)(0)π(0) to date: A(CP)(D(0)→K(S)(0)π(0))=(-0.28±0.19±0.10)%. We also report the first measurements of CP asymmetries in the decays D(0)→K(S)(0)η and D(0)→K(S)(0)η': A(CP)(D(0)→K(S)(0)η)=(+0.54±0.51±0.16)% and A(CP)(D(0)→K(S)(0)η')=(+0.98±0.67±0.14)%, respectively.

Evidence for the suppressed decay B(-)→DK(-), D→K(+)π(-).

The suppressed decay chain B(-)→DK(-), D→K(+)π(-), where D indicates a D(¯)(0) or D(0) state, provides important information on the CP-violating angle ϕ(3). We measure the ratio R(DK) of the decay rates to the favored mode B(-)→DK(-), D→K(-)π(+) to be R(DK)=[1.63(-0.41)(+0.44)(stat)(-0.13)(+0.07)(syst)]×10(-2), which indicates the first evidence of the signal with a significance of 4.1σ. We also measure the asymmetry A(DK) between the charge-conjugate decays to be A(DK)=-0.39(-0.28)(+0.26)(stat)(-0.03)(+0.04)(syst). The results are based on the full 772×10(6) BB(¯) pair data sample collected at the Υ(4S) resonance with the Belle detector.

Search for CP violation in τ±â†’K(S)0π±ντ decays at Belle.

We report on a search for CP violation in τ(±)→K(S)(0)π(±)ν(τ) decays using a data sample of 699 fb(-1) collected by the Belle experiment at the KEKB electron-positron asymmetric-energy collider. The CP asymmetry is measured in four bins of the invariant mass of the K(S)(0)π(±) system and found to be compatible with zero with a precision of O(10(-3)) in each mass bin. Limits for the CP violation parameter Im(η(S)) are given at the 90% confidence level. These limits are |Im(η(S))| < 0.026 or better, depending on the parametrization used to describe the hadronic form factors, and improve upon previous limits by 1 order of magnitude.

Observation of B(s)°â†’J/ψf0(980) and evidence for B(s)°â†’J/ψf0(1370).

We report the observation of B(s)°â†’J/ψf0(980) and evidence for B(s)°â†’J/ψf0(1370), which are CP eigenstate decay modes. These results are obtained from 121.4 fb⁻¹ of data collected at the Υ(5S) resonance with the Belle detector at the KEKB e(+)e⁻ collider. We measure the branching fractions B(B(s)°â†’J/ψf0(980); f0(980)→π(+)π⁻)=(1.16(-0.19)(+0.31)(stat)(-0.17)(+0.15)(syst)(-0.18)(+0.26)(N(B(s)((*))B(s)((*)))))×10⁻4 with a significance of 8.4σ, and B(B(s)°â†’J/ψf0(1370); f0(1370)→π(+)π⁻)=(0.34(-0.14)(+0.11)(stat)(-0.02)(+0.03)(syst)(-0.05)(+0.08)(N(B(s)((*))B(s)((*)))))×10⁻4 with a significance of 4.2σ. The last error listed is due to uncertainty in the number of produced B(s)((*))B(s)((*)) pairs.

Observation of X(3872)→J/ψγ and search for X(3872)→ψ'γ in B decays.

We report a study of B→(J/ψγ)K and B→(ψ'γ)K decay modes using 772×106 B ̅B events collected at the Υ(4S) resonance with the Belle detector at the KEKB energy-asymmetric e(+)e(-) collider. We observe X(3872)→J/ψγ and report the first evidence for χ(c2)→J/ψγ in B→(X_{c ̅cγ)K decays, while in a search for X(3872)→ψ'γ no significant signal is found. We measure the branching fractions, B(B(±)→X(3872)K(±))B(X(3872)→J/ψγ)=(1.78(-0.44)(+0.48)±0.12)×10(-6), B(B(±)→χ(c2)K(±))=(1.11(-0.34)(+0.36)±0.09)×10(-5), B(B(±)→X(3872)K(±))B(X(3872)→ψ'γ)<3.45×106 (upper limit at 90% C.L.), and also provide upper limits for other searches.

Observation of D+ → K(+)η(') and search for CP violation in D+ → π(+)η(') decays.

We report the first observation of the doubly Cabibbo-suppressed decays D(+)→K(+)η((')) using a 791 fb(-1) data sample collected with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider. The ratio of the branching fractions of doubly Cabibbo-suppressed relative to singly Cabibbo-suppressed D(+)→π(+)η((')) decays are B(D(+)→K(+)η)/B(D(+)→π(+)η)=(3.06±0.43±0.14)% and B(D(+)→K(+)η')/B(D(+)→π(+)η')=(3.77±0.39±0.10)%. From these, we find that the relative final-state phase difference between the tree and annihilation amplitudes in D(+) decays, δ(TA), is (72±9)° or (288±9)°. We also report the most precise measurements of CP asymmetries to date: A(CP)(D(+)→π(+)η)=(+1.74±1.13±0.19)% and A(CP)(D(+)→π(+)η')=(-0.12±1.12±0.17)%.