Search Results (120 total)

Using the CLEO detector at the Cornell Electron Storage Ring, we have studied the distribution of kinematic variables in the decay Λ_c⁺→Λe⁺ν_e. By performing a four-dimensional maximum likelihood fit, we determine the form factor ratio, R=f₂/f₁=-0.31±0.05(stat)±0.04(syst), the pole mass, M_pole=[2.21±0.08(stat)±0.14(syst)]  GeV/c², and the decay asymmetry parameter of the Λ_c⁺, α_Λc=-0.86±0.03(stat)±0.02(syst), for ⟨q²⟩=0.67 (GeV/c²)². We compare the angular distributions of the Λ_c⁺ and Λ̅ _c^- and find no evidence for CP violation: A_Λc=(α_Λc+α_{Λ̅ c}) / (α_Λc-α_{Λ̅ c})=0.00±0.03(stat)±0.01(syst)±0.02, where the third error is from the uncertainty in the world average of the CP-violating parameter, A_Λ, for Λ→pπ^-.

Using the CLEO detector at the Cornell Electron-positron Storage Ring, we have measured the scaled momentum spectra, dσ/dx_p, and the inclusive production cross sections of the charm mesons D⁺, D⁰, D^⋆+, and D^⋆0 in e⁺e^- annihilation at about 10.5 GeV center of mass energy, excluding the decay products of B mesons. The statistical accuracy and momentum resolution are superior to previous measurements at this energy.

We report on a search for CP violation in the decay of D⁰ and D̅ ⁰ to K_S⁰π⁺π^-. The data come from an integrated luminosity of 9.0   fb^-1 of e⁺e^- collisions at sqrt[s]≈10  GeV recorded with the CLEO II.V detector. The resonance substructure of this decay is well described by ten quasi-two-body decay channels plus a small nonresonant component. We observe no evidence for CP violation in the amplitudes that describe the decay D⁰→K_S⁰π⁺π^-.

We report a new measurement of the B-meson semileptonic decay momentum spectrum that has been made with a sample of 9.4 fb^-1 of e⁺e^- data collected with the CLEO II detector at the Υ(4S) resonance. Electrons from primary semileptonic decays and secondary charm decays were separated by using charge and angular correlations in Υ(4S) events with a high-momentum lepton and an additional electron. We determined the semileptonic branching fraction to be B(B→Xe⁺ν_e)=(10.91±0.09±0.24)% from the normalization of the electron-energy spectrum. We also measured the moments of the electron-energy spectrum with minimum energies from 0.6 to 1.5 GeV.

We present a measurement of the composition of B meson inclusive semileptonic decays using 9.4 fb^-1 of e⁺e^- data taken with the CLEO detector at the Υ(4S) resonance. In addition to measuring the charged lepton kinematics, the neutrino four-vector is inferred using the hermiticity of the detector. We perform a maximum likelihood fit over the full three-dimensional differential decay distribution for the fractional contributions from the B→X_clν processes with X_c=D, D^*, D^**, and nonresonant X_c, and the process B→X_ulν. From the fit results we extract the first and second moments of the M_X² and q² distributions with minimum lepton-energy requirements of 1.0 GeV and 1.5 GeV. We find 〈M_X²-M_D²〉=(0.456±0.014±0.045±0.109) GeV²/c⁴ with a minimum lepton energy of 1.0 GeV and 〈M_X²-M_D²〉=(0.293±0.012±0.033±0.048) GeV²/c⁴ with minimum lepton energy of 1.5 GeV. The uncertainties are from statistics, detector systematic effects, and model dependence, respectively. As a test of the HQET and OPE calculations, the results for the M_X² moment as a function of the minimum lepton energy requirement are compared to the predictions.

We present the first evidence for the production of Υ(1D) states in the four-photon cascade, Υ(3S)→γχ_b(2P), χ_b(2P)→γΥ(1D), Υ(1D)→γχ_b(1P), χ_b(1P)→γΥ(1S), followed by the Υ(1S) annihilation into e⁺e^- or μ⁺μ^-. The signal has a significance of 10.2 standard deviations. The measured product branching ratio for these five decays, (2.5±0.5±0.5)×10^-5, is consistent with the theoretical estimates. The data are dominated by the production of one Υ(1D) state consistent with the J=2 assignment. Its mass is determined to be (10161.1±0.6±1.6) MeV, which is consistent with the predictions from potential models and lattice QCD calculations. We also searched for Υ(3S)→γχ_b(2P), χ_b(2P)→γΥ(1D), followed by either Υ(1D)→ηΥ(1S) or Υ(1D)→π⁺π^-Υ(1S). We find no evidence for such decays and set upper limits on the product branching ratios.

We present the first study of the vector (Wess-Zumino) current in τ^-→K^-π^-K⁺ν_τ decay using data collected with the CLEO III detector at the Cornell Electron Storage Ring. We determine the quantitative contributions to the decay width from the vector and axial vector currents. Within the framework of a model by Kühn and Mirkes, we identify the quantitative contributions to the total decay rate from the intermediate states ωπ, ρ^(′)π, and K^*K.

The CLEO Collaboration has made the first observations of hadronic transitions among bottomonium (bb̅ ) states other than the dipion transitions among Υ(nS) states. In our study of Υ(3S) decays, we find a significant signal for Υ(3S)→γωΥ(1S) that is consistent with radiative decays Υ(3S)→γχ_b1,2(2P), followed by χ_b1,2(2P)→ωΥ(1S). The branching ratios we obtain are B[χ_b1(2P)→ωΥ(1S)]=(1.63_-0.31-0.15^+0.35+0.16)% and B[χ_b2(2P)→ωΥ(1S)]=(1.10_-0.28-0.10^+0.32+0.11)%, in which the first error is statistical and the second is systematic.

Using a 13.7 fb^-1 data sample collected with the CLEO II and II.V detectors, we report new branching fraction measurements for two Cabibbo-suppressed decay modes of the D⁺ meson: B(D⁺→π⁺π⁰)=(1.31±0.17±0.09±0.09)×10^-3 and B(D⁺→K⁺K⁰)=(5.24±0.43±0.20±0.34)×10^-3 which are significant improvements over past measurements. The errors reflect statistical and systematical uncertainties as well as the uncertainty in the absolute D⁺ branching fraction scale. We also set the first 90% confidence level upper limit on the branching fraction of the doubly Cabibbo-suppressed decay mode B(D⁺→K⁺π⁰)<4.2×10^-4.

We report on the observation of the η_c^′(2¹S₀), the radial excitation of the η_c(1¹S₀) ground state of charmonium, in the two-photon fusion reaction γγ→η_c^′→K_S⁰K^±π^∓ in 13.6   fb^-1 of CLEO II/II.V data and 13.1   fb^-1 of CLEO III data. We obtain M(η_c^′)=3642.9±3.1(stat)±1.5(syst)  MeV and M(η_c)=2981.8±1.3(stat)±1.5(syst)  MeV. The corresponding values of hyperfine splittings between ¹S₀ and ³S₁ states are ΔM_hf(1S)=115.1±2.0  MeV and ΔM_hf(2S)=  43.1±3.4  MeV. Assuming that the η_c and η_c^′ have equal branching fractions to K_SKπ, we obtain Γ_γγ(η_c^′)=1.3±0.6  keV.

Using the CLEO III detector at CESR, we have measured the branching ratio of the decay Ξ_c⁰→pK^-K^-π⁺ relative to Ξ_c⁰→Ξ^-π⁺. We find B(Ξ_c⁰→pK^-K^-π⁺)/B(Ξ_c⁰→Ξ^-π⁺)=0.35±0.06(stat)±0.03(syst). In the resonant substructure of this mode, we find evidence for Ξ_c⁰ decays to pK^*̅ (892)⁰K^-, and measure B(Ξ_c⁰→pK^*̅ (892)⁰K^-)×B(K^*̅ (892)⁰→K^-π⁺)/B(Ξ_c⁰→Ξ^-π⁺)=0.14±0.03(stat)±0.01(syst) and B(Ξ_c⁰→pK^-K^-π⁺)/B(Ξ_c⁰→Ξ^-π⁺)=0.21±0.04(stat)±0.02(syst) for the non-K^*̅ (892)⁰Ξ_c⁰→pK^-K^-π⁺ decays.

We report on determinations of |V_ub| resulting from studies of the branching fraction and q² distributions in exclusive semileptonic B decays that proceed via the b→u transition. Our data set consists of the 9.7×10⁶ BB̅ meson pairs collected at the Υ(4S) resonance with the CLEO II detector. We measure B(B⁰→π^-l⁺ν)=(1.33±0.18±0.11±0.01±0.07)×10^-4 and B(B⁰→ρ^-l⁺ν)=(2.17±0.34_-0.54^+0.47±0.41±0.01)×10^-4, where the errors are statistical, experimental systematic, systematic due to residual form-factor uncertainties in the signal, and systematic due to residual form-factor uncertainties in the cross-feed modes, respectively. We also find B(B⁺→ηl⁺ν)=(0.84±0.31±0.16±0.09)×10^-4, consistent with what is expected from the B→πlν mode and quark model symmetries. We extract |V_ub| using light-cone sum rules for 0<~q²<16 GeV² and lattice QCD for 16 GeV²<~q²<q_max². Combining both intervals yields |V_ub|=(3.24±0.22±0.13_-0.39^+0.55±0.09)×10^-3 for πlν, and |V_ub|=(3.00±0.21_-0.35-0.38^+0.29+0.49±0.28)×10^-3 for ρlν, where the errors are statistical, experimental systematic, theoretical, and ρlν form-factor shape, respectively. Our combined value from both decay modes is |V_ub|=(3.17±0.17_-0.17-0.39^+0.16+0.53±0.03)×10^-3.

We present final measurements of 13 charmless hadronic B decay modes from the CLEO experiment. The decay modes include the ten ππ, Kπ, and KK final states and new limits on dibaryonic final states, pp̅ , pΛ̅ , and ΛΛ̅ , as well as a new determination of the ratio B(B→DK)/B(B→Dπ). The results are based on the full CLEO II and CLEO III data samples totalling 15.3 fb^-1 at the Υ(4S), and supercede previously published results.

Using 13.5 fb^-1 of e⁺e^- annihilation data collected with the CLEO II detector, we have observed a narrow resonance decaying to D_s^*+π⁰ with a mass near 2.46 GeV/c². The search for such a state was motivated by the recent discovery by the BaBar Collaboration of a narrow state at 2.32 GeV/c², the D_sJ^*(2317)⁺, that decays to D_s⁺π⁰. Reconstructing the D_s⁺π⁰ and D_s^*+π⁰ final states in CLEO data, we observe peaks in both of the corresponding reconstructed mass difference distributions, ΔM(D_sπ⁰)=M(D_sπ⁰)-M(D_s) and ΔM(D_s^*π⁰)=M(D_s^*π⁰)-M(D_s^*), both of them at values near 350 MeV/c². We interpret these peaks as signatures of two distinct states, the D_sJ^*(2317)⁺ plus a new state, designated as the D_sJ(2463)⁺. Because of the similar ΔM values, each of these states represents a source of background for the other if photons are lost, ignored or added. A quantitative accounting of these reflections confirms that both states exist. We have measured the mean mass differences 〈ΔM(D_sπ⁰)〉=350.0±1.2 (stat)±1.0 (syst) MeV/c² for the D_sJ^*(2317)⁺ state, and 〈ΔM(D_s^*π⁰)〉=351.2±1.7 (stat)±1.0 (syst) MeV/c² for the new D_sJ(2463)⁺ state. We have also searched, but find no evidence, for decays of the two states via the channels D_s^*+γ, D_s⁺γ, and D_s⁺π⁺π^-. The observations of the two states at 2.32 and 2.46 GeV/c², in the D_s⁺π⁰ and D_s^*+π⁰ decay channels, respectively, are consistent with their interpretations as cs̅ mesons with an orbital angular momentum L=1 and spin and parity J^P=0⁺ and 1⁺.

We have searched for the baryon-containing radiative penguin decays B^-→Λp̅ γ and B^-→Σ⁰p̅ γ, using a sample of 9.7×10⁶ BB̅ events collected at the Υ(4S) with the CLEO detector. We find no evidence for either, and set 90% confidence level upper limits of B(B^-→Λp̅ γ)+0.3B(B^-→Σ⁰p̅ γ)]_{Eγ>2.0 GeV}<3.3×10^-6, [B(B^-→Σ⁰p̅ γ)+0.4B(B^-→Λp̅ γ)]_{Eγ>2.0 GeV}<6.4×10^-6. From the latter, we estimate B(B→X_sγ,X_s containing baryons)_{Eγ>2.0 GeV}<3.8×10^-5. This limit implies upper limits on corrections to CLEO’s recent measurement of branching fraction, mean photon energy, and variance in photon energy from b→sγ that are less than half the combined statistical and systematic errors quoted on these quantities.

Using data collected on the Υ(4S) resonance and the nearby continuum by the CLEO detector at the Cornell Electron Storage Ring, we have searched for the semileptonic decay of B mesons to ep̅ inclusive final states. We obtain an upper limit for b→c decays of B(B→p̅ e^-ν̅ _eX)<5.9×10^-4. For the b→u decay, we find an upper limit of B(B^-→pp̅ e^-ν̅ _e)<1.2×10^-3 based on a V-A model, while a phase space model gives an upper limit of B(B^-→pp̅ e^-ν̅ _e)<5.2×10^-3. All upper limits are measured at the 90% confidence level.

Based on a measurement of high momentum η^′ production in B decays, we determine the charmless inclusive B→η^′X_nc branching fraction in the lab-frame momentum interval 2.0<P_η^′<2.7 GeV/c. Using 9.7×10⁶BB̅ pairs collected at the Υ(4S) center-of-mass energy with the CLEO II and II.V detector configurations, we find B(B→η^′X_nc)=[4.6±1.1±0.4±0.5]×10^-4 in the 2.0<P_η^′<2.7 GeV/c momentum range, where the uncertainties are statistical, systematic, and from subtraction of background from B decays to charm, respectively.

We report on a search for a CP-violating asymmetry in the charmless hadronic decay B→K^*(892)^±π^∓, using 9.1 fb^-1 of integrated luminosity produced at sqrt[s]=10.58 GeV and collected with the CLEO detector. We find A_CP(B→K^*(892)^±π^∓)=0.26_-0.34^+0.33(stat)_-0.08^+0.10(syst), giving an allowed interval of [-0.31,0.78] at the 90% confidence level.

Using 9.1 fb^-1 of e⁺e^- data collected at the Υ(4S) with the CLEO detector using the Cornell Electron Storage Ring, measurements are reported for both the branching fractions and the helicity amplitudes for the decays B^-→D^*0ρ^- and B⁰→D^*+ρ^-. The fraction of longitudinal polarization in B⁰→D^*+ρ^- is found to be consistent with that in B⁰→D^*+l^-ν̅ at q²=M_ρ², indicating that the factorization approximation works well. The longitudinal polarization in the B^- mode is similar. The measurements also show evidence of nontrivial final-state interaction phases for the helicity amplitudes.

From electron-positron collision data collected with the CLEO detector operating at Cornell Electron Storage Ring near sqrt[s]=10.6  GeV, improved measurements of the branching fractions for τ decays into three explicitly identified hadrons and a neutrino are presented as B(τ^-→π^-π⁺π^-ν_τ)=(9.13±0.05±0.46)%, B(τ^-→K^-π⁺π^-ν_τ)=(3.84±0.14±0.38)×10^-3, B(τ^-→K^-K⁺π^-ν_τ)=(1.55±0.06±0.09)×10^-3, and B(τ^-→K^-K⁺K^-ν_τ)<3.7×10^-5 at 90% C.L., where the uncertainties are statistical and systematic, respectively.

We measure the primary lepton momentum spectrum in B̅ →Xlν̅ decays, for p_l>~1.5 GeV/c in the B rest frame. From this, we calculate various moments of the spectrum. In particular, we find R₀≡∫_{1.7 GeV}(dΓ/dE_sl)dE_l/∫_{1.5 GeV}(dΓ/dE_sl)dE_l=0.6187±0.0014_stat±0.0016_sys and R₁≡∫_{1.5 GeV}E_l(dΓ/dE_sl)dE_l/∫_{1.5 GeV}(dΓ/dE_sl)dE_l=(1.7810±0.0007_stat±0.0009_sys) GeV. We use these moments to determine non-perturbative parameters governing the semileptonic width. In particular, we extract the heavy quark expansion parameters Λ̅ =(0.39±0.03_stat±0.06_sys±0.12_th) GeV and λ₁=(-0.25±0.02_stat±0.05_sys±0.14_th) GeV². The theoretical constraints used are evaluated through order 1/M_B³ in the non-perturbative expansion and β₀α_s² in the perturbative expansion. We use these parameters to extract |V_cb| from the world average of the semileptonic width and find |V_cb|=(40.8±0.5_Γsl±0.4_{(λ1,Λ̅ )exp}±0.9_th)×10^-3. In addition, we extract the short range b-quark mass m_b^1S=(4.82±0.07_exp±0.11_th) GeV/c². Finally, we discuss the implications of our measurements for the theoretical understanding of inclusive semileptonic processes.

Using the CLEO II detector at CESR, we measure the η^′ energy spectra in Υ(1S) decays that we compare with models of the η^′g^*g form factor. This form factor, especially at large η^′ energies, may provide an explanation of the large rate for B→X_sη^′. Our data do not support a large anomalous coupling at higher q² and thus the large η^′ rate remains a mystery, possibly requiring a non-standard-model explanation.

Using 13.8   fb^-1 of data collected at or just below the Υ(4S) with the CLEO detector, we report the result of a search for the flavor changing neutral current process D⁰→γγ. We observe no significant signal for this decay mode and determine 90% confidence level upper limits on the branching fractions B(D⁰→γγ)/B(D⁰→π⁰π⁰)<0.033 and B(D⁰→γγ)<2.9×10^-5.