Search Results (146 total)

We have searched for the charmless hadronic decay of B⁰ mesons into two neutral pions. Using 9.13 fb^-1 taken at the Υ(4S) with the CLEO detector, we obtain an improved upper limit for the branching fraction B(B⁰→π⁰π⁰)<5.7×10^-6 at the 90% confidence level.

We have studied two-body charmless decays of the B meson into the final states ρ⁰ρ⁰, K^*0ρ⁰, K^*0K^*0, K^*0K̅ ^*0, K^*+ρ⁰, K^*+K̅ ^*0, and K^*+K^*- using only decay modes with charged daughter particles. Using 9.7×10⁶ BB̅ pairs collected with the CLEO detector, we place 90% confidence level upper limits on the branching fractions (1.4–14.1)×10^-5, depending on final state and polarization.

We have searched for the two-body decay of the B meson to a light pseudoscalar meson h  =  π^±,K^±,K_S⁰ and a massless neutral feebly interacting particle X⁰ such as the familon, the Nambu-Goldstone boson associated with a spontaneously broken global family symmetry. We find no significant signal by analyzing a data sample containing 9.7×10⁶ BB̅ mesons collected with the CLEO detector at the Cornell Electron Storage Ring, and set 90% C.L. upper limits B(B^±→h^±X⁰)  =  4.9×10^-5 and B(B⁰→K_S⁰X⁰)  =  5.3×10^-5. These limits correspond to a lower bound of approximately 10⁸ GeV on the family symmetry breaking scale with vector coupling involving the third generation of quarks.

We have measured the first and second moments of the hadronic mass-squared distribution in B→X_cℓν, for P_lepton>1.5 GeV/c. We find 〈M_X²-M̅ _D²〉  =  0.251±0.066 GeV², 〈(M_X²-〈M_X²〉)²〉  =  0.576±0.170 GeV⁴, where M̅ _D is the spin-averaged D meson mass. From that first moment and the first moment of the photon energy spectrum in b→sγ, we find the heavy quark effective theory parameter λ₁ (in the modified minimal subtraction renormalization scheme, to order 1/M_B³ and β₀α_s²) to be -0.24±0.11 GeV². Using these first moments and the B semileptonic width, and assuming parton-hadron duality, we obtain |V_cb|  =  0.0404±0.0013.

We have measured the branching fraction and photon energy spectrum for the radiative penguin process b→sγ. We find B(b→sγ)  =  (3.21±0.43±0.27_-0.10^+0.18)×10^-4, where the errors are statistical, systematic, and from theory corrections. We obtain first and second moments of the photon energy spectrum above 2.0 GeV, 〈E_γ〉  =  2.346±0.032±0.011 GeV, and 〈E_γ²〉-〈E_γ〉²  =  0.0226±0.0066±0.0020 GeV², where the errors are statistical and systematic. From the first moment, we obtain (in the modified minimal subtraction renormalization scheme, to order 1/M_B³ and β₀α_s²) the heavy quark effective theory parameter Λ̅  =  0.35±0.08±0.10 GeV.

We search for CP nonconservation in the decays of τ leptons produced via e⁺e^- annihilation at sqrt[s]∼10.6 GeV. The method uses correlated decays of pairs of τ leptons, each decaying to the ππ⁰ν_τ final state. The search is done within the framework of a model with a scalar boson exchange. In an analysis of a data sample corresponding to 12.2×10⁶ produced τ pairs collected with the CLEO detector, we find no evidence of violation of CP symmetry. We obtain a limit on the imaginary part of the coupling constant parametrizing the relative contribution of diagrams that would lead to CP violation to be -0.046<Im(Λ)<0.022 at 90% C.L. This result provides a restriction on CP nonconservation in tau lepton decays. As a cross-check, we study the decay angular distribution and perform a model-independent search for a CP violation effect of a scalar exchange in single τ→ππ⁰ν_τ decays. The limit on the imaginary part of the τ scalar coupling is -0.033<Im(Λ)<0.089 at 90% C.L.

We report on the observation of B̅ →D^*π⁺π^-π^-π⁰ decays. The branching ratios for D^*+ and D^*0 are (1.72±0.14±0.24)% and (1.80±0.24±0.27)%, respectively. Each final state has a D^*ωπ^- component, with branching ratios (0.29±0.03±0.04)% and (0.45±0.10±0.07)% for the D^*+ and D^*0 modes, respectively. We also observe B̅ →Dωπ^- decays. The branching ratios for D⁺ and D⁰ are (0.28±0.05±0.04)% and (0.41±0.07±0.06)%, respectively. A spin parity analysis of the ωπ^- system in the Dωπ^- final state shows a preference for a wide 1^- resonance. A fit to the ωπ^- mass spectrum finds a central mass of (1349±25_-5⁺¹⁰) MeV and width of (547±86_-45⁺⁴⁶) MeV. We identify this object as the ρ(1450) or the ρ^′.

We report on a search for the decay B⁺→D^*+K_S⁰ and its charge conjugate with the CLEO detector at the Cornell Electron Storage Ring (CESR). No candidates are found in 9.10 fb^-1 of data. The background is estimated to be 0.29±0.05 leading to an upper limit B(B⁺→D^*+K⁰)=9.5×10^-5 (90% confidence level).

We present an observation and time-integrated rate measurement of the decay D⁰→K⁺π^-π⁰ produced in 9 fb^-1 of e⁺e^- collisions near the ϒ(4S) resonance. The signal is inconsistent with an upward fluctuation of the background by 4.9 standard deviations. We measured the time-integrated rate of D⁰→K⁺π^-π⁰ normalized to the rate of D⁰̅ →K⁺π^-π⁰ to be 0.0043_-0.0010^+0.0011 (stat)±0.0007 (syst). This decay can be produced by doubly Cabibbo-suppressed decays or by the D⁰ evolving into a D⁰̅ through mixing, followed by a Cabibbo-favored decay to K⁺π^-π⁰. We also found the CP asymmetry A  =  (9_-22⁺²⁵)% be consistent with zero.

Using 12.7 fb^-1 of data collected with the CLEO detector at CESR, we observed two-photon production of the cc̅ states χ_c0 and χ_c2 in their decay to π⁺π^-π⁺π^-. We measured Γ_γγ(χ_c)×B(χ_c→π⁺π^-π⁺π^-) to be 75±13(stat)±8(syst) eV for the χ_c0 and 6.4±1.8(stat)±0.8(syst) eV for the χ_c2, implying Γ_γγ(χ_c0)  =  3.76±0.65(stat)±0.41(syst)±1.69(br) keV and Γ_γγ(χ_c2)  =  0.53±0.15(stat)±0.06(syst)±0.22(br) keV. Also, cancellation of dominant experimental and theoretical uncertainties permits a precise comparison of Γ_γγ(χ_c0)/Γ_γγ(χ_c2), evaluated to be 7.4±2.4(stat)±0.5(syst)±0.9(br), with QCD-based predictions.

We have measured the CP asymmetry A_CP≡[Γ(b→sγ)-Γ(b̅ →s̅ γ)]/[Γ(b→sγ)+Γ(b̅ →s̅ γ)] to be A_CP  =  (-0.079±0.108±0.022) (1.0±0.030), implying that, at 90% confidence level, A_CP lies between -0.27 and +0.10. These limits rule out some extreme non-standard-model predictions, but are consistent with most, as well as with the standard model.

We have measured the charge asymmetry in like-sign dilepton yields from B⁰B̅ ⁰ meson decays using the CLEO detector at the Cornell Electron Storage Ring. We find a_ℓℓ⁰≡[N(ℓ⁺ℓ⁺)-N(ℓ^-ℓ^-)]/[N(ℓ⁺ℓ⁺)+N(ℓ^-ℓ^-)]  =  +0.013±0.050±0.005. We combine this result with a previous, independent measurement and obtain Re(ε_B)/(1+|ε_B|²)  =  +0.0035±0.0103±0.0015 (uncertainties are statistical and systematic, respectively) for the CP impurity parameter, ε_B.

Using 13.7 fb^-1 of data recorded by the CLEO detector at the Cornell Electron Storage Ring, we investigate the spectrum of charmed baryons which decay into Λ_c⁺π^-π⁺ and are more massive than the Λ_c⁺(2625) baryon. We find evidence for two new states: one is broad and has an invariant mass roughly 480 MeV above that of the Λ_c⁺ baryon; the other is narrow with an invariant mass of 596±1±2 MeV above the Λ_c⁺ mass.

The τ decays to six-pion final states have been studied with the CLEO detector at the Cornell Electron Storage Ring. The measured branching fractions are B(τ^-→2π^-π⁺3π⁰ν_τ)  =  (2.2±0.3±0.4)×10^-4 and B(τ^-→3π^-2π⁺π⁰ν_τ)  =  (1.7±0.2±0.2)×10^-4. A search for substructure in these decays shows that they are saturated by intermediate states with η or ω mesons. We present the first observation of the decay τ^-→2π^-π⁺ων_τ and the branching fraction is measured to be (1.2±0.2±0.1)×10^-4. The measured branching fractions are in good agreement with the isospin expectations but somewhat below the conserved-vector-current predictions.

Using 13.7 fb^-1 of data recorded by the CLEO detector at Cornell Electron Storage Ring, we report evidence of two new charmed baryons: one decaying into Ξ_c^0′π⁺ with the subsequent decay Ξ_c^0′→Ξ_c⁰γ, and its isospin partner decaying into Ξ_c^+′π^- followed by Ξ_c^+′→Ξ_c⁺γ. We measure the following mass differences for the two states: M(Ξ_c⁰γπ⁺)-M(Ξ_c⁰)  =  318.2±1.3±2.9 MeV and M(Ξ_c⁺γπ^-)-M(Ξ_c⁺)  =  324.0±1.3±3.0 MeV. We interpret these new states as the J^P  =  1 / 2^- Ξ_c1 particles, the charmed-strange analogs of the Λ_c1⁺(2593).

Using 13.6 fb^-1 of continuum two-jet e⁺e^-→cc̅ events collected with the CLEO detector, we have searched for baryon number correlations at the primary quark level. We have measured the likelihood for a Λ_c⁺ charmed baryon to be produced in the hemisphere opposite a Λ̅ _c^- relative to the likelihood for a Λ_c⁺ charmed baryon to be produced opposite an anticharmed meson D̅ ; in all cases, the reconstructed hadrons must have momentum greater than 2.3 GeV/c. We find that, given a Λ̅ _c^- (reconstructed in five different decay modes), a Λ_c⁺ is observed in the opposite hemisphere (0.72±0.11)% of the time (not corrected for efficiency). By contrast, given a D̅ in one hemisphere, a Λ_c⁺ is observed in the opposite hemisphere only (0.21±0.02)% of the time. Normalized to the total number of either Λ̅ _c^- or D̅ “tags,” it is therefore 3.52±0.45±0.42 times more likely to find a Λ_c⁺ opposite a Λ̅ _c^- than a D̅ meson. This enhancement is not observed in the JETSET 7.3 e⁺e^-→cc̅ Monte Carlo simulation.

The CLEO experiment at the CESR collider has used 13.7 fb^-1 of data to search for the production of the Ω_c⁰ (css ground state) in e⁺e^- collisions at sqrt[s]≃10.6 GeV. The modes used to study the Ω_c⁰ are Ω^-π⁺, Ω^-π⁺π⁰, Ξ^-K^-π⁺π⁺, Ξ⁰K^-π⁺, and Ω^-π⁺π⁺π^-. We observe a signal of 40.4±9.0(stat) events at a mass of 2694.6±2.6(stat)±1.9(syst) MeV/c², for all modes combined.

We have studied two-body charmless hadronic decays of B mesons into the final states φK and φK^*. Using 9.7 million BB̅ pairs collected with the CLEO II detector, we observe the decays B^-→φK^- and B⁰→φK^*0 with the following branching fractions: B(B^-→φK^-)  =  (5.5_-1.8^+2.1±0.6)×10^-6 and B(B⁰→φK^*0)  =  (11.5_-3.7-1.7^+4.5+1.8)×10^-6. We also see evidence for the decays B⁰→φK⁰ and B^-→φK^*-. However, since the statistical significance is not overwhelming for these modes, we determine upper limits of <12.3×10^-6 and <22.5×10^-6 ( 90% confidence level), respectively.

Using the CLEO II detector at the Cornell Electron Storage Ring we have measured the Ξ_c⁰ decay asymmetry parameter in the decay Ξ_c⁰→Ξ^-π⁺. We find α_Ξc⁰α_Ξ=0.26±0.18(stat)_-0.04^+0.05(syst); using the world average value of α_Ξ=-0.456±0.014 we obtain α_Ξc⁰=-0.56±0.39(stat)_-0.09^+0.10(syst). The physically allowed range of a decay asymmetry parameter is -1<α<+1. Our result prefers a negative value: α_Ξc⁰ is <0.1 at the 90% C.L. The central value occupies the middle of the theoretically expected range but is not yet precise enough to choose between models.

We use data collected with the CLEO II detector to perform a high-statistics measurement of the resonant substructure in D⁰→K^-π⁺π⁰ decays. We find that the Dalitz plot is well represented by a combination of seven quasi-two-body decay channels [K^*0π⁰, K^-ρ, K^*-π⁺, K₀(1430)^-π⁺, K₀(1430)⁰π⁰, K^-ρ⁺(1700), and K^*(1680)^-π⁺], plus a small non-resonant component. We see no evidence of a scalar κ→K^-π⁺ resonance in the mass range recently reported by other groups. Using the amplitudes and phases from this analysis, we calculate an integrated CP asymmetry of -0.031±0.086.

We report results of a search for B→τν in a sample of 9.7×10⁶ charged B meson decays. We exclusively reconstruct the companion B̅ decay to suppress background. We set an upper limit on the branching fraction B(B→τν)<8.4×10^-4 at 90% confidence level. We also establish B(B^±→K^±νν̅ )<2.4×10^-4 at 90% confidence level.

We analyze 9.7×10⁶ BB̅ pairs recorded with the CLEO detector to determine the production ratio of charged to neutral B-meson pairs produced at the ϒ(4S) resonance. We measure the rates for B⁰→J/ψK^(*)0 and B⁺→J/ψK^(*)+ decays and use the world-average B-meson lifetime ratio to extract the relative widths f_+- / f₀₀  =  Γ(ϒ(4S)→B⁺B^-) / Γ(ϒ(4S)→B⁰B̅ ⁰)  =  1.04±0.07(stat)±0.04(syst). With the assumption that f_+-+f₀₀  =  1, we obtain f₀₀  =  0.49±0.02(stat)±0.01(syst) and f_+-  =  0.51±0.02(stat)±0.01(syst). This production ratio and its uncertainty apply to all exclusive B-meson branching fractions measured at the ϒ(4S) resonance.

We report the first observation of exclusive decays of the type B→D^*NN̅ X, where N is a nucleon. Using a sample of 9.7×10⁶BB̅ pairs collected with the CLEO detector operating at the Cornell Electron Storage Ring, we measure the branching fractions B(B⁰→D^*-pp̅ π⁺)  =  (6.5_-1.2^+1.3±1.0)×10^-4 and B(B⁰→D^*-pn̅ )  =  (14.5_-3.0^+3.4±2.7)×10^-4. Antineutrons are identified by their annihilation in the CsI electromagnetic calorimeter.

The Λ_c⁺ lifetime is measured using 9.0 fb^-1 of e⁺e^- annihilation data collected on or just below the ϒ(4S) resonance with the CLEO II.V detector at CESR. Using an unbinned maximum likelihood fit, the Λ_c⁺ lifetime is measured to be 179.6±6.9(stat)±4.4(syst) fs. The precision of this colliding beam measurement is comparable to other measurements, which are based on fixed-target experiments, with different systematic uncertainties.

We have searched for CP-violating asymmetries in neutral charm meson decays in 13.7 fb^-1 of e⁺e^- collision data at sqrt[s]≈10.6 GeV with the CLEO detector. The measured asymmetries in the rate of D⁰ and D⁰̅ decays to K_S⁰π⁰, π⁰π⁰ and K_S⁰K_S⁰ final states are (+0.1±1.3)%, (+0.1±4.8)% and (-23±19)%, respectively.