RESUMEN
We present the study of B[over ¯]^{0}âΣ_{c}(2455)^{0,++}π^{±}p[over ¯] decays based on 772×10^{6} BB[over ¯] events collected with the Belle detector at the KEKB asymmetric-energy e^{+}e^{-} collider. The Σ_{c}(2455)^{0,++} candidates are reconstructed via their decay to Λ_{c}^{+}π^{∓} and Λ_{c}^{+} decays to pK^{-}π^{+}, pK_{S}^{0}, and Λπ^{+} final states. The corresponding branching fractions are measured to be B(B[over ¯]^{0}âΣ_{c}(2455)^{0}π^{+}p[over ¯])=(1.09±0.06±0.07)×10^{-4} and B(B[over ¯]^{0}âΣ_{c}(2455)^{++}π^{-}p[over ¯])=(1.84±0.11±0.12)×10^{-4}, which are consistent with the world average values with improved precision. A new structure is found in the M_{Σ_{c}(2455)^{0,++}π^{±}} spectrum with a significance of 4.2σ including systematic uncertainty. The structure is possibly an excited Λ_{c}^{+} and is tentatively named Λ_{c}(2910)^{+}. Its mass and width are measured to be (2913.8±5.6±3.8) MeV/c^{2} and (51.8±20.0±18.8) MeV, respectively. The products of branching fractions for the Λ_{c}(2910)^{+} are measured to be B(B[over ¯]^{0}âΛ_{c}(2910)^{+}p[over ¯])×B(Λ_{c}(2910)^{+}âΣ_{c}(2455)^{0}π^{+})=(9.5±3.6±1.6)×10^{-6} and B(B[over ¯]^{0}âΛ_{c}(2910)^{+}p[over ¯])×B(Λ_{c}(2910)^{+}âΣ_{c}(2455)^{++}π^{-})=(1.24±0.35±0.10)×10^{-5}. Here, the first and second uncertainties are statistical and systematic, respectively.
RESUMEN
We study B^{+}âπ^{+}π^{0}π^{0} using 711 fb^{-1} of data collected at the Ï(4S) resonance with the Belle detector at the KEKB asymmetric-energy e^{+}e^{-} collider. We measure an inclusive branching fraction of (19.0±1.5±1.4)×10^{-6} and an inclusive CP asymmetry of (9.2±6.8±0.7)%, where the first uncertainties are statistical and the second are systematic, and a B^{+}âρ(770)^{+}π^{0} branching fraction of (11.2±1.1±0.9_{-1.6}^{+0.8})×10^{-6}, where the third uncertainty is due to possible interference with B^{+}âρ(1450)^{+}π^{0}. We present the first observation of a structure around 1 GeV/c^{2} in the π^{0}π^{0} mass spectrum, with a significance of 6.4σ, and measure a branching fraction to be (6.9±0.9±0.6)×10^{-6}. We also report a measurement of local CP asymmetry in this structure.
RESUMEN
Using the data sample of 980 fb^{-1} collected with the Belle detector operating at the KEKB asymmetric-energy e^{+}e^{-} collider, we present the results of an investigation of the Λπ^{+} and Λπ^{-} invariant mass distributions looking for substructure in the decay Λ_{c}^{+}âΛπ^{+}π^{+}π^{-}. We find a significant signal in each mass distribution. When interpreted as resonances, we find for the Λπ^{+} (Λπ^{-}) combination a mass of 1434.3±0.6(stat)±0.9(syst) MeV/c^{2} [1438.5±0.9(stat)±2.5(syst) MeV/c^{2}], an intrinsic width of 11.5±2.8(stat)±5.3(syst) MeV/c^{2} [33.0±7.5(stat)±23.6(syst) MeV/c^{2}] with a significance of 7.5σ (6.2σ). As these two signals are very close to the K[over ¯]N threshold, we also investigate the possibility of a K[over ¯]N cusp, and find that we cannot discriminate between these two interpretations due to the limited size of the data sample.
RESUMEN
The first simultaneous determination of the absolute value of the Cabibbo-Kobayashi-Maskawa matrix element V_{ub} using inclusive and exclusive decays is performed with the full Belle data set at the Ï(4S) resonance, corresponding to an integrated luminosity of 711 fb^{-1}. We analyze collision events in which one B meson is fully reconstructed in hadronic modes. This allows for the reconstruction of the hadronic X_{u} system of the semileptonic bâuâν[over ¯]_{â} decay. We separate exclusive Bâπâν[over ¯]_{â} decays from other inclusive BâX_{u}âν[over ¯]_{â} and backgrounds with a two-dimensional fit that utilizes the number of charged pions in the X_{u} system and the four-momentum transfer q^{2} between the B and X_{u} systems. Combining our measurement with information from lattice QCD and QCD calculations of the inclusive partial rate as well as external experimental information on the shape of the Bâπâν[over ¯]_{â} form factor, we determine |V_{ub}^{excl}|=(3.78±0.23±0.16±0.14)×10^{-3} and |V_{ub}^{incl}|=(3.88±0.20±0.31±0.09)×10^{-3}, respectively, with the uncertainties being the statistical error, systematic errors, and theory errors. The ratio of |V_{ub}^{excl}|/|V_{ub}^{incl}|=0.97±0.12 is compatible with unity.
RESUMEN
We report on a search for a heavy Majorana neutrino in the decays τ^{-}âπ^{-}ν_{h}, ν_{h}âπ^{±}â^{∓}, â=e, µ. The results are obtained using the full data sample of 988 fb^{-1} collected with the Belle detector at the KEKB asymmetric energy e^{+}e^{-} collider, which contains 912×10^{6} ττ pairs. We observe no significant signal and set 95% CL upper limits on the couplings of the heavy right-handed neutrinos to the conventional standard model left-handed neutrinos in the mass range 0.2-1.6 GeV/c^{2}. This is the first study of a mixed couplings of heavy neutrinos to τ leptons and light-flavor leptons.
RESUMEN
We report the first measurement of the Michel parameter ξ^{'} in the τ^{-}âµ^{-}ν[over ¯]_{µ}ν_{τ} decay with a new method proposed just recently. The measurement is based on the reconstruction of the τ^{-}âµ^{-}ν[over ¯]_{µ}ν_{τ} events with subsequent muon decay in flight in the Belle central drift chamber. The analyzed data sample of 988 fb^{-1} collected by the Belle detector corresponds to approximately 912×10^{6} τ^{+}τ^{-} pairs. We measure ξ^{'}=0.22±0.94(stat)±0.42(syst), which is in agreement with the standard model prediction of ξ^{'}=1. Statistical uncertainty dominates in this study, being a limiting factor, while systematic uncertainty is well under control. Our analysis proved the practicability of this promising method and its prospects for further precise measurement in future experiments.
RESUMEN
We search for a light Higgs boson (A^{0}) decaying into a τ^{+}τ^{-} or µ^{+}µ^{-} pair in the radiative decays of Ï(1S). The production of Ï(1S) mesons is tagged by Ï(2S)âπ^{+}π^{-}Ï(1S) transitions, using 158×10^{6} Ï(2S) events accumulated with the Belle detector at the KEKB asymmetric energy electron-positron collider. No significant A^{0} signals in the mass range from the τ^{+}τ^{-} or µ^{+}µ^{-} threshold to 9.2 GeV/c^{2} are observed. We set the upper limits at 90% credibility level (C.L.) on the product branching fractions for Ï(1S)âγA^{0} and A^{0}âτ^{+}τ^{-} varying from 3.8×10^{-6} to 1.5×10^{-4}. Our results represent an approximately twofold improvement on the current world best upper limits for the Ï(1S)âγA^{0}(âτ^{+}τ^{-}) production. For A^{0}âµ^{+}µ^{-}, the upper limits on the product branching fractions for Ï(1S)âγA^{0} and A^{0}âµ^{+}µ^{-} are at the same level as the world average limits, and vary from 3.1×10^{-7} to 1.6×10^{-5}. The upper limits at 90% credibility level on the Yukawa coupling f_{Ï(1S)} and mixing angle sinθ_{A^{0}} are also given.
RESUMEN
We report the first evidence for X(3872) production in two-photon interactions by tagging either the electron or the positron in the final state, exploring the highly virtual photon region. The search is performed in e^{+}e^{-}âe^{+}e^{-}J/ψπ^{+}π^{-}, using 825 fb^{-1} of data collected by the Belle detector operated at the KEKB e^{+}e^{-} collider. We observe three X(3872) candidates, where the expected background is 0.11±0.10 events, with a significance of 3.2σ. We obtain an estimated value for Γ[over Ë]_{γγ}B(X(3872)âJ/ψπ^{+}π^{-}) assuming the Q^{2} dependence predicted by a cc[over ¯] meson model, where -Q^{2} is the invariant mass squared of the virtual photon. No X(3915)âJ/ψπ^{+}π^{-} candidates are found.
RESUMEN
The first measurements of differential branching fractions of inclusive semileptonic BâX_{u}â^{+}ν_{â} decays are performed using the full Belle data set of 711 fb^{-1} of integrated luminosity at the Ï(4S) resonance and for â=e, µ. With the availability of these measurements, new avenues for future shape-function model-independent determinations of the Cabibbo-Kobayashi-Maskawa matrix element |V_{ub}| can be pursued to gain new insights in the existing tension with respect to exclusive determinations. The differential branching fractions are reported as a function of the lepton energy, the four-momentum-transfer squared, light-cone momenta, the hadronic mass, and the hadronic mass squared. They are obtained by subtracting the backgrounds from semileptonic BâX_{c}â^{+}ν_{â} decays and other processes, and corrected for resolution and acceptance effects.
RESUMEN
The experimental results on the ratios of branching fractions R(D)=B(B[over ¯]âDτ^{-}ν[over ¯]_{τ})/B(B[over ¯]âDâ^{-}ν[over ¯]_{â}) and R(D^{*})=B(B[over ¯]âD^{*}τ^{-}ν[over ¯]_{τ})/B(B[over ¯]âD^{*}â^{-}ν[over ¯]_{â}), where â denotes an electron or a muon, show a long-standing discrepancy with the standard model predictions, and might hint at a violation of lepton flavor universality. We report a new simultaneous measurement of R(D) and R(D^{*}), based on a data sample containing 772×10^{6} BB[over ¯] events recorded at the Ï(4S) resonance with the Belle detector at the KEKB e^{+}e^{-} collider. In this analysis the tag-side B meson is reconstructed in a semileptonic decay mode and the signal-side τ is reconstructed in a purely leptonic decay. The measured values are R(D)=0.307±0.037±0.016 and R(D^{*})=0.283±0.018±0.014, where the first uncertainties are statistical and the second are systematic. These results are in agreement with the standard model predictions within 0.2, 1.1, and 0.8 standard deviations for R(D), R(D^{*}), and their combination, respectively. This work constitutes the most precise measurements of R(D) and R(D^{*}) performed to date as well as the first result for R(D) based on a semileptonic tagging method.
RESUMEN
We report the first observation of the radiative decay of the Ï(1S) into a charmonium state. The significance of the observed signal of Ï(1S)âγχ_{c1} is 6.3 standard deviations including systematics. The branching fraction is calculated to be B[Ï(1S)âγχ_{c1}]=[4.7_{-1.8}^{+2.4}(stat)_{-0.5}^{+0.4}(sys)×10^{-5}]. We also searched for Ï(1S) radiative decays into χ_{c0,2} and η_{c}(1S,2S), and set upper limits on their branching fractions. These results are obtained from a 24.9 fb^{-1} data sample collected with the Belle detector at the KEKB asymmetric-energy e^{+}e^{-} collider at a center-of-mass energy equal to the Ï(2S) mass using Ï(1S) tagging by the Ï(2S)âÏ(1S)π^{+}π^{-} transitions.
RESUMEN
We present the first measurements of absolute branching fractions of Ξ_{c}^{0} decays into Ξ^{-}π^{+}, ΛK^{-}π^{+}, and pK^{-}K^{-}π^{+} final states. The measurements are made using a dataset comprising (772±11)×10^{6} BB[over ¯] pairs collected at the Ï(4S) resonance with the Belle detector at the KEKB e^{+}e^{-} collider. We first measure the absolute branching fraction for B^{-}âΛ[over ¯]_{c}^{-}Ξ_{c}^{0} using a missing-mass technique; the result is B(B^{-}âΛ[over ¯]_{c}^{-}Ξ_{c}^{0})=(9.51±2.10±0.88)×10^{-4}. We subsequently measure the product branching fractions B(B^{-}âΛ[over ¯]_{c}^{-}Ξ_{c}^{0})B(Ξ_{c}^{0}âΞ^{-}π^{+}), B(B^{-}âΛ[over ¯]_{c}^{-}Ξ_{c}^{0})B(Ξ_{c}^{0}âΛK^{-}π^{+}), and B(B^{-}âΛ[over ¯]_{c}^{-}Ξ_{c}^{0})B(Ξ_{c}^{0}âpK^{-}K^{-}π^{+}) with improved precision. Dividing these product branching fractions by the result for B^{-}âΛ[over ¯]_{c}^{-}Ξ_{c}^{0} yields the following branching fractions: B(Ξ_{c}^{0}âΞ^{-}π^{+})=(1.80±0.50±0.14)%, B(Ξ_{c}^{0}âΛK^{-}π^{+})=(1.17±0.37±0.09)%, and B(Ξ_{c}^{0}âpK^{-}K^{-}π^{+})=(0.58±0.23±0.05)%. For the above branching fractions, the first uncertainties are statistical and the second are systematic. Our result for B(Ξ_{c}^{0}âΞ^{-}π^{+}) can be combined with Ξ_{c}^{0} branching fractions measured relative to Ξ_{c}^{0}âΞ^{-}π^{+} to yield other absolute Ξ_{c}^{0} branching fractions.
RESUMEN
We report the first observation of the double strange baryon Ξ(1620)^{0} in its decay to Ξ^{-}π^{+} via Ξ_{c}^{+}âΞ^{-}π^{+}π^{+} decays based on a 980 fb^{-1} data sample collected with the Belle detector at the KEKB asymmetric-energy e^{+}e^{-} collider. The mass and width are measured to be 1610.4±6.0(stat)_{-4.2}^{+6.1} (syst) MeV/c^{2} and 59.9±4.8(stat)_{-7.1}^{+2.8}(syst) MeV, respectively. We obtain 4.0σ evidence of the Ξ(1690)^{0} with the same data sample. These results shed light on the structure of hyperon resonances with strangeness S=-2.
RESUMEN
We report the first observation of the spontaneous polarization of Λ and Λ[over ¯] hyperons transverse to the production plane in e^{+}e^{-} annihilation, which is attributed to the effect arising from a polarizing fragmentation function. For inclusive Λ/Λ[over ¯] production, we also report results with subtracted feed-down contributions from Σ^{0} and charm. This measurement uses a dataset of 800.4 fb^{-1} collected by the Belle experiment at or near a center-of-mass energy of 10.58 GeV. We observe a significant polarization that rises with the fractional energy carried by the Λ/Λ[over ¯] hyperon.
RESUMEN
We report the first observation of the hadronic transition Ï(4S)âη^{'}Ï(1S), using 496 fb^{-1} data collected at the Ï(4S) resonance with the Belle detector at the KEKB asymmetric-energy e^{+}e^{-} collider. We reconstruct the η^{'} meson through its decays to ρ^{0}γ and to π^{+}π^{-}η, with ηâγγ. We measure B(Ï(4S)âη^{'}Ï(1S))=[3.43±0.88(stat)±0.21(syst)]×10^{-5}, with a significance of 5.7σ.
RESUMEN
We report the results of a search for the rare, purely leptonic decay B^{-}âµ^{-}ν[over ¯]_{µ} performed with a 711 fb^{-1} data sample that contains 772×10^{6} BB[over ¯] pairs, collected near the Ï(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^{-}âµ^{-}ν[over ¯]_{µ})=(6.46±2.22±1.60)×10^{-7} or a frequentist 90% confidence level interval on the B^{-}âµ^{-}ν[over ¯]_{µ} branching fraction of [2.9,10.7]×10^{-7}.
RESUMEN
We report the observation of Ï(2S)âγη_{b}(1S) decay based on an analysis of the inclusive photon spectrum of 24.7 fb^{-1} of e^{+}e^{-} collisions at the Ï(2S) center-of-mass energy collected with the Belle detector at the KEKB asymmetric-energy e^{+}e^{-} collider. We measure a branching fraction of B[Ï(2S)âγη_{b}(1S)]=(6.1_{-0.7-0.6}^{+0.6+0.9})×10^{-4} and derive an η_{b}(1S) mass of 9394.8_{-3.1-2.7}^{+2.7+4.5} MeV/c^{2}, where the uncertainties are statistical and systematic, respectively. The significance of our measurement is greater than 7 standard deviations, constituting the first observation of this decay mode.
RESUMEN
Using data recorded with the Belle detector, we observe a new excited hyperon, an Ω^{*-} candidate decaying into Ξ^{0}K^{-} and Ξ^{-}K_{S}^{0} with a mass of 2012.4±0.7(stat)±0.6(syst) MeV/c^{2} and a width of Γ=6.4_{-2.0}^{+2.5}(stat)±1.6(syst) MeV. The Ω^{*-} is seen primarily in Ï(1S),Ï(2S), and Ï(3S) decays.
RESUMEN
We report the first measurement of the τ lepton polarization P_{τ}(D^{*}) in the decay B[over ¯]âD^{*}τ^{-}ν[over ¯]_{τ} as well as a new measurement of the ratio of the branching fractions R(D^{*})=B(B[over ¯]âD^{*}τ^{-}ν[over ¯]_{τ})/B(B[over ¯]âD^{*}â^{-}ν[over ¯]_{â}), where â^{-} denotes an electron or a muon, and the τ is reconstructed in the modes τ^{-}âπ^{-}ν_{τ} and τ^{-}âρ^{-}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.
RESUMEN
We report a study of the decay D^{0}âK_{S}^{0}K_{S}^{0} using 921 fb^{-1} of data collected at or near the Ï(4S) and Ï(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}âK_{S}^{0}K_{S}^{0})=(-0.02±1.53±0.02±0.17)%, and the branching fraction is B(D^{0}âK_{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}âK_{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.