Measurement of the branching fraction of the decay B+ →π+π-ℓ+νℓ in fully reconstructed events at Belle

We present an analysis of the exclusive B+→π+π-ℓ+νℓ decay, where ℓ represents an electron or a muon, with the assumption of charge-conjugation symmetry and lepton universality. The study exploits the full ϒ(4S) data sample collected by the Belle detector, corresponding to 711 fb-1 of integrated luminosity. Events are selected by fully reconstructing one B meson in hadronic decay modes, subsequently determining the properties of the other B meson. We extract the signal yields using a binned maximum-likelihood fit to the missing-mass squared distribution in bins of the invariant mass of the two pions or the momentum transfer squared. We measure a total branching fraction of B(B+→π+π-ℓ+νℓ)=[22.7-1.6+1.9(stat)±3.5(syst)]×10-5, where the uncertainties are statistical and systematic, respectively. This result is the first reported measurement of this decay

Search for Z′ →μ+μ- in the Lμ-Lτ gauge-symmetric model at Belle

We search for a new gauge boson Z′ that couples only to heavy leptons and their corresponding neutrinos in the process e+e-→Z′(→μ+μ-)μ+μ-, using a 643 fb-1 data sample collected by the Belle experiment at or near the ϒ(1S,2S,3S,4S,5S) resonances at the KEKB collider. While previous searches for Z′ performed a data-based estimation of the initial state radiation effect, our search for the Z′ is the first to include effects due to initial state radiation in the signal simulated samples that were used in estimating the detection efficiency. No signal is observed in the Z′ mass range of 0.212-10 GeV/c2, and we set an upper limit on the coupling strength, g′, constraining the possible Z′ contribution to the anomalous magnetic dipole moment of the muon

Measurement of the resonant and nonresonant branching ratios in Ξc0 → Ξ0K+K-

Using the entire data sample of 980 fb-1 integrated luminosity collected with the Belle detector at the KEKB asymmetric-energy e+e- collider, we present an amplitude analysis measuring the branching fractions of the Cabibbo-allowed, W-exchange resonant decay Ξc0→Ξ0φ(→K+K-) with a polarized φ and the nonresonant decay via a direct process Ξc0→Ξ0K+K-. We present these measurements, relative to the normalization mode Ξ-π+, and find branching ratios B(Ξc0→Ξ0φ(→K+K-))(BΞc0→Ξ-π+)=0.036±0.004(stat.)±0.002(syst.) and B(Ξc0→Ξ0K+K-)B(Ξc0→Ξ-π+)=0.039±0.004(stat.)±0.002(syst.), which suggest that only minor cusping peaks occur in the combinatorial background of ω∗-→Ξ0K- due to these Ξc0 decays

Search for charged lepton flavor violating decays of ϒ (1S)

We present a search for the charged lepton-flavor-violating decays ϒ(1S) →ℓ±ℓ′∓ and radiative charged lepton-flavour-violating decays ϒ(1S) → γℓ±ℓ′∓ [ℓ,ℓ′ = e, μ, τ] using the 158 million ϒ(2S) sample collected by the Belle detector at the KEKB collider. This search uses ϒ(1S) mesons produced in ϒ(2S) → π+π− ϒ(1S) transitions. We do not find any significant signal, so we provide upper limits on the branching fractions at the 90% confidence level. [Figure not available: see fulltext.

Search for B0 meson decays into Λ and missing energy with a hadronic tagging method at Belle

We present a search for the decays of B0 mesons into a final state containing a Λ baryon and missing energy. These results are obtained from a 711 fb-1 data sample that contains 772×106 BB¯ pairs and was collected near the (4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. We use events in which one B meson is fully reconstructed in a hadronic decay mode and require the remainder of the event to consist of only a single Λ. No evidence for these decays is found, and we set 90% confidence level upper limits on the branching fractions in the range 2.1-3.8×10-5. This measurement provides the world\u27s most restrictive limits, with implications for baryogenesis and dark matter production

Measurements of q2 moments of inclusive B →xcℓ+νℓ decays with hadronic tagging

We present the measurement of the first to fourth order moments of the four-momentum transfer squared, q2, of inclusive B→Xcℓ+νℓ decays using the full Belle dataset of 711 fb-1 of integrated luminosity at the (4S) resonance where ℓ=e, μ. The determination of these moments and their systematic uncertainties open new pathways to determine the absolute value of the Cabibbo-Kobayashi-Maskawa matrix element Vcb using a reduced set of matrix elements of the heavy quark expansion. In order to identify and reconstruct the Xc system, we reconstruct one of the two B-mesons using machine learning techniques in fully hadronic decay modes. The moments are measured with progressively increasing threshold selections on q2 starting with a lower value of 3.0 GeV2 in steps of 0.5 GeV2 up to a value of 10.0 GeV2. The measured moments are further unfolded, correcting for reconstruction and selection effects as well as QED final state radiation. We report the moments separately for electron and muon final states and observe no lepton flavor universality violating effects

Search for the decay Bs0 →η′η

We report the results of the first search for the decay Bs0→η′η using 121.4 fb-1 of data collected at the I (5S) resonance with the Belle detector at the KEKB asymmetric-energy e+e-collider. We observe no significant signal and set a 90% confidence-level upper limit of 6.5×10-5 on the branching fraction of this decay

Measurement of B (Bs →dsX) with Bs semileptonic tagging

We report the first direct measurement of the inclusive branching fraction B(Bs→DsX) via Bs tagging in e+e-→ (5S) events. Tagging is accomplished through a partial reconstruction of semileptonic decays Bs→DsXℓν, where X denotes unreconstructed additional hadrons or photons and ℓ is an electron or muon. With 121.4 fb-1 of data collected at the (5S) resonance by the Belle detector at the KEKB asymmetric-energy e+e- collider, we obtain B(Bs→DsX)=(60.2±5.8±2.3)%, where the first uncertainty is statistical and the second is systematic

Measurement of branching fractions and search for CP violation in D \u3csup\u3e0\u3c/sup\u3e → π \u3csup\u3e+\u3c/sup\u3e π \u3csup\u3e −\u3c/sup\u3e η, D \u3csup\u3e0\u3c/sup\u3e → K \u3csup\u3e+\u3c/sup\u3e K \u3csup\u3e −\u3c/sup\u3e η, and D \u3csup\u3e0\u3c/sup\u3e → ϕη at Belle

We measure the branching fractions and CP asymmetries for the singly Cabibbo-suppressed decays D0 → π+π−η, D0 → K+K−η, and D0 → ϕη, using 980 fb−1 of data from the Belle experiment at the KEKB e+e− collider. We obtainB(D0→π+π−η)=[1.22±0.02(stat)±0.02(syst)±0.03(Bref)]×10−3,B(D0→K+K−η)=[1.80−0.06+0.07(stat)±0.04(syst)±0.05(Bref)]×10−4,B(D0→ϕη)=[1.84±0.09(stat)±0.06(syst)±0.05(Bref)]×10−4, where the third uncertainty (Bref) is from the uncertainty in the branching fraction of the reference mode D0 → K−π+η. The color-suppressed decay D0 → ϕη is observed for the first time, with very high significance. The results for the CP asymmetries areACP(D0π+π−η)=[0.9±1.2(stat)±0.5(syst)]%,ACP(D0→K+K−η)=[−1.4±3.3(stat)±1.1(syst)]%,ACP(D0→ϕη)=[−1.9±4.4(stat)±0.6(syst)]%. The results for D0 → π+π−η are a significant improvement over previous results. The branching fraction and ACP results for D0 → K+K−η, and the ACP result for D0 → ϕη, are the first such measurements. No evidence for CP violation is found in any of these decays. [Figure not available: see fulltext.

Measurements of the branching fractions of Λc+ →pη and Λc+ →pπ0 decays at Belle

We report measurements of the branching fractions of singly Cabibbo-suppressed decays Λc+→pη and Λc+→pπ0 using the full Belle data sample corresponding to an integrated luminosity of 980.6 fb-1. The data were collected by the Belle detector at the KEKB e+e- asymmetric energy collider. A clear Λc+ signal is seen in the invariant mass distribution of pη. The fitted number of signal events of the Λc+→pη process is 7734±263; from this, we measure the ratio of branching fractions B(Λc+→pη)/B(Λc+→pK-π+)=[2.258±0.077(stat)±0.122(syst)]×10-2, from which we infer the branching fraction B(Λc+→pη)=[1.42±0.05(stat)±0.11(syst)]×10-3. In addition, no significant signal for Λc+→pπ0 is found, so an upper limit on the branching fraction of B(Λc+→pπ0)\u3c8.0×10-5 at a 90% credibility level is set, more than 3 times better than the best current upper limit