Search Results (152 total)

With the first data sample collected by the CLEO-c detector at the ψ(3770) resonance we have studied four exclusive semileptonic decays of the D⁰ meson. Our results include the first observation and absolute branching fraction measurement for D⁰→ρ^-e⁺ν_e and improved measurements of the absolute branching fractions for D⁰ decays to K^-e⁺ν_e, π^-e⁺ν_e, and K^*-e⁺ν_e.

Using data collected at the ψ(3770) resonance with the CLEO-c detector at the Cornell e⁺e^- storage ring, we present improved measurements of the absolute branching fractions of D⁺ decays to K̅ ⁰e⁺ν_e, π⁰e⁺ν_e, K̅ ^*0e⁺ν_e, and ρ⁰e⁺ν_e, and the first observation and absolute branching fraction measurement of D⁺→ωe⁺ν_e. We also report the most precise tests to date of isospin invariance in semileptonic D⁰ and D⁺ decays.

Using 55.8  pb^-1 of e⁺e^- collisions recorded at the ψ(3770) resonance with the CLEO-c detector at CESR, we determine absolute hadronic branching fractions of charged and neutral D mesons using a double tag technique. Among measurements for three D⁰ and six D⁺ modes, we obtain reference branching fractions B(D⁰→K^-π⁺)=(3.91±0.08±0.09)% and B(D⁺→K^-π⁺π⁺)=(9.5±0.2±0.3)%, where the uncertainties are statistical and systematic, respectively. Final state radiation is included in these branching fractions by allowing for additional, unobserved, photons in the final state. Using a determination of the integrated luminosity, we also extract the cross sections σ(e⁺e^-→D⁰D̅ ⁰)=(3.60±0.07_-0.05^+0.07)  nb and σ(e⁺e^-→D⁺D^-)=(2.79±0.07_-0.04^+0.10)  nb.

In e⁺e^- collisions recorded using the CLEO II.V detector we have studied the Cabibbo suppressed decay of D⁰→π⁺π^-π⁰ with the initial flavor of the D⁰ tagged by the decay D^*+→D⁰π⁺. We use the Dalitz-plot analysis technique to measure the resonant substructure in this final state and observe ρπ and nonresonant contributions by fitting for their amplitudes and relative phases. We describe the ππ S wave with a K-matrix formalism and limit this contribution to the rate to be <2.5%@95% confidence level, in contrast to the large rate observed in D⁺→π⁺π^-π⁺ decay. Using the amplitudes and phases from this analysis, we calculate an integrated CP asymmetry of 0.01_-0.07^+0.09±0.05.

The resonant substructure in D⁰→K_S⁰π⁺π^- decays is described by a combination of ten quasi two-body intermediate states which include both CP-even and CP-odd eigenstates and one doubly Cabibbo suppressed channel. We present a formalism that connects the variation in D⁰ decay time over the Dalitz plot with the mixing parameters, x and y, that describe off-shell and on-shell D⁰-D̅ ⁰ mixing. We analyze the CLEO II.V data sample and find the parameters x and y are consistent with zero. We limit (-4.5<x<9.3)% and (-6.4<y<3.6)% at the 95% confidence level.

The rare τ lepton decays to four explicitly identified hadrons have been studied with the CLEO detector at the Cornell Electron Storage Ring using (7.56±0.15)  fb^-1 of data collected near sqrt[s]=10.58  GeV. The first statistically significant measurements of B(τ^-→K^-π⁺π^-π⁰ν_τ,excluding K⁰)=(7.4±0.8±1.1)×10^-4 and B(τ^-→K^-K⁺π^-π⁰ν_τ)=(5.5±1.4±1.2)×10^-5 are presented, including the first observation of the decay τ^-→K^-ων_τ with branching fraction, (4.1±0.6±0.7)×10^-4. We publish the first upper limit for B(τ^-→K^-K⁺K^-π⁰ν_τ)<4.8(6.1)×10^-6 at 90% (95%) confidence level. We measure for the first time the invariant mass distributions, which together with the branching fraction measurements are important ingredients that can be used to extract the standard model parameters, the strange quark mass, and the Cabibbo-Kobayashi-Maskawa element V_us.

We present measurements of the branching fractions for J/ψ→e⁺e^- and μ⁺μ^- using 3M ψ(2S) decays collected with the CLEO detector operating at the CESR e⁺e^- collider. We obtain B(J/ψ→e⁺e^-)=(5.945±0.067±0.042)% and B(J/ψ→μ⁺μ^-)=(5.960±0.065±0.050)%, leading to an average of B(J/ψ→ℓ⁺ℓ^-)=(5.953±0.056±0.042)% and a ratio of B(J/ψ→e⁺e^-)/B(J/ψ→μ⁺μ^-)=(99.7±1.2±0.6)%, all consistent with, but more precise than, previous measurements.

We describe new measurements of the inclusive and exclusive branching fractions for ψ(2S) transitions to J/ψ using e⁺e^- collision data collected with the CLEO detector operating at CESR. All branching fractions and ratios of branching fractions reported here represent either the most precise measurements to date or the first direct measurements. Indirectly and in combination with other CLEO measurements, we determine B(χ_cJ→γJ/ψ) and B[ψ(2S)→ light hadrons].

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^-.

We analyze 13.8  fb^-1 of the integrated e⁺e^- luminosity collected at 10.6 GeV center-of-mass energy with the CLEO II and CLEO II.V detectors to study exclusive two-photon production of hadrons with masses below 1.7  GeV/c² decaying into the K_S⁰K^±π^∓ final state. We observe two statistically significant enhancements in the η(1475) mass region. These enhancements have large transverse momentum which rules them out as being due to pseudoscalar resonances but is consistent with the production of axial-vector mesons. We use tagged two-photon events to study the properties of the observed enhancements and associate them with the production of f₁(1285) and f₁(1420). Our nonobservation of η(1475) is inconsistent by more than 2 standard deviations with the first observation of this resonance in two-photon collisions by the L3 experiment. We present our estimates for 90% confidence level upper limits on the products of two-photon partial widths of light pseudoscalar hadrons and their branching fractions into K_S⁰(π⁺π^-)K^±π^∓.

Using the CLEO II.V detector observing e⁺e^- collisions at around 10.6 GeV we search for neutral D mixing in semileptonic D⁰ decays tagged in charged D^* decays. Combining the results from the Keν and K^*eν channels we find that the rate for D mixing is less than 0.0078 at 90% C.L.

Using data recorded by the CLEO III detector at the Cornell electron storage ring (CESR), we have made measurements of some properties of the Σ_c^*++ and Σ_c^*0 charmed baryons. In particular: Γ(Σ_c^*++)=14.4_-1.5^+1.6±1.4  MeV, M(Σ_c^*++)-M(Λ_c⁺)=231.5±0.4±0.3  MeV, Γ(Σ_c^*0)=16.6_-1.7^+1.9±1.4  MeV,M(Σ_c^*0)-M(Λ_c⁺)=231.4±0.5±0.3  MeV.

We report on a search for the recently reported X(3872) state using 15.1   fb^-1 of e⁺e^- data taken in the sqrt[s]=9.46–11.30  GeV region. Separate searches for the production of the X(3872) in untagged γγ fusion and e⁺e^- annihilation following initial state radiation are made by taking advantage of the unique angular correlation between the leptons from the decay J/ψ→l⁺l^- in X(3872) decay to π⁺π^-J/ψ. No signals are observed in either case, and 90% confidence upper limits are established as (2J+1)Γ_γγ(X(3872))B(X→π⁺π^-J/ψ)<12.9  eV and Γ_ee(X(3872))B(X→π⁺π^-J/ψ)<8.3  eV.

We have studied the inclusive photon spectra in Υ(2S) and Υ(3S) decays using a large statistics data sample obtained with the CLEO III detector. We present the most precise measurements of electric dipole (E1) photon transition rates and photon energies for Υ(2S)→γχ_bJ(1P) and Υ(3S)→γχ_bJ(2P) (J=0, 1, 2). We measure the rate for a rare E1 transition Υ(3S)→γχ_b0(1P) for the first time. We also set upper limits on the rates for the hindered magnetic dipole (M1) transitions to the η_b(1S) and η_b(2S) states.

Using the CLEO-III detector at CESR we study e⁺e^- collisions in the center-of-mass energy close to, or above, Λ_b⁰Λ̅ _b⁰ production threshold. We search for evidence of Λ_b⁰Λ̅ _b⁰ resonance production and set upper limits based on inclusive hadron production as a barometer of Λ_b⁰Λ̅ _b⁰ production.

Using CLEO data collected from CESR e⁺e^- collisions at the ψ(2S) resonance and nearby continuum at sqrt[s]=3.67  GeV, we report the first significantly nonzero measurements of light vector-pseudoscalar hadron pair production (including ρπ, ωπ, ρη, and K^*0K⁰̅ ) and the π⁺π^-π⁰ final state, both from ψ(2S) decays and direct e⁺e^- annihilation.

The decay branching fractions of the three narrow Υ resonances to μ⁺μ^- have been measured by analyzing about 4.3   fb^-1 e⁺e^- data collected with the CLEO III detector. The branching fraction B(Υ(1S)→μ⁺μ^-)=(2.49±0.02±0.07)% is consistent with the current world average, but B(Υ(2S)→μ⁺μ^-)=(2.03±0.03±0.08)% and B(Υ(3S)→μ⁺μ^-)=(2.39±0.07±0.10)% are significantly larger than prior results. These new muonic branching fractions imply a narrower total decay width for the Υ(2S) and Υ(3S) resonances and lower other branching fractions that rely on these decays in their determination.

We investigate the decays D⁰→π^-ℓ⁺ν and D⁰→K^-ℓ⁺ν, where ℓ is e or μ, using approximately 7  fb^-1 of data collected with the CLEO III detector. We find R₀≡B(D⁰→π^-e⁺ν)/B(D⁰→K^-e⁺ν)=0.082±0.006±0.005. Fits to the kinematic distributions of the data provide parameters describing the form factor of each mode. Combining the form factor results and R₀ gives |f₊^π(0)|²|V_cd|²/|f₊^K(0)|²|V_cs|²=0.038_-0.007-0.003^+0.006+0.005.

In 60   pb^-1 of data taken on the ψ(3770) resonance with the CLEO-c detector, we find eight D⁺→μ⁺ν decay candidates that are mostly signal, containing only one estimated background. Using this statistically compelling sample, we measure a value of B(D⁺→μ⁺ν)=(3.5±1.4±0.6)×10^-4, and determine f_D⁺=(202±41±17)  MeV.

We have studied the inclusive photon spectrum in ψ(2S) decays using the CLEO III detector. We present the most precise measurements of electric dipole (E1) photon transition rates for ψ(2S)→γχ_cJ(1P) (J=0,1,2). We also confirm the hindered magnetic dipole (M1) transition, ψ(2S)→γη_c(1S). However, the direct M1 transition ψ(2S)→γη_c(2S) observed by the Crystal Ball as a narrow peak at a photon energy of 91 MeV is not found in our data.