Search Results (318 total)

We evaluate the partial widths for internal conversions in the Higgs decays to two photons. For the Higgs masses of interest at the CERN LHC in the range of 100–150 GeV, the conversions to pairs of fermions represent a significant fraction of Higgs decays.

Using the current world’s largest data sample of ψ(3770) decays, we present results of a search for the non-DD̅ decay ψ(3770)→K_S⁰K_L⁰. We find no signal, and obtain an upper limit of σ(e⁺e^-→ψ(3770)→K_S⁰K_L⁰)<0.07  pb at 90% confidence level (CL). Our result tests a theoretical prediction for the upper bound on B(ψ(3770)→K_S⁰K_L⁰) based on a charmonia-mixing model.

Using a sample of 3.08×10⁶ ψ(2S) decays collected at sqrt[s]=3.686  GeV with the CLEO detector at the Cornell Electron Storage Ring, we have measured the branching fractions for ψ(2S) decays to pseudoscalar pairs π⁺π^-, K⁺K^- and K_S⁰K_L⁰. We obtain B(ψ(2S)→π⁺π^-)<2.1×10^-5 (90% C.L.), B(ψ(2S)→K⁺K^-)=(6.3±0.6(stat)±0.3(syst))×10^-5, and B(ψ(2S)→K_S⁰K_L⁰)=(5.8±0.8(stat)±0.4(syst))×10^-5. The branching fractions allow extraction of the relative phase Δ=(95±15)° and strength ratio R=(2.5±0.4) of the three-gluon and one-photon amplitudes for these modes.

Using data taken with the CLEO III detector at the Cornell Electron Storage Ring, we have investigated the direct photon spectrum in the decays Υ(1S)→γgg, Υ(2S)→γgg, Υ(3S)→γgg. The latter two of these are first measurements. Our analysis procedures differ from previous ones in the following ways: (a) background estimates (primarily from π⁰ decays) are based on isospin symmetry rather than a determination of the π⁰ spectrum, which permits measurement of the Υ(2S) and Υ(3S) direct photon spectra without explicit corrections for π⁰ backgrounds from, e.g., χ_bJ states, (b) we estimate the branching fractions with a parametrized functional form (exponential) used for the background, and c) we use the high-statistics sample of Υ(2S)→ππΥ(1S) to obtain a tagged sample of Υ(1S)→γ+X events, for which there are no QED backgrounds. We determine values for the ratio of the inclusive direct photon decay rate to that of the dominant three-gluon decay Υ→ggg  (R_γ=B(ggγ)/B(ggg)) to be R_γ(1S)=(2.70±0.01±0.13±0.24)%, R_γ(2S)=(3.18±0.04±0.22±0.41)%, and R_γ(3S)=(2.72±0.06±0.32±0.37)%, where the errors shown are statistical, systematic, and theoretical model dependent, respectively. Given a value of Q², one can estimate a value for the strong coupling constant α_s(Q²) from R_γ.

Using 420  pb^-1 of data collected on the Υ(5S) resonance with the CLEO III detector, we reconstruct B mesons in 25 exclusive decay channels to measure or set upper limits on the decay rate of Υ(5S) into B meson final states. We measure the inclusive B cross section to be σ(Υ(5S)→BB̅ (X))=(0.177±0.030±0.016)  nb and make the first measurements of the production rates of σ(Υ(5S)→B^*B̅ ^*)=(0.131±0.025±0.014)  nb and σ(Υ(5S)→BB̅ ^*)=(0.043±0.016±0.006)  nb, respectively. We set 90% confidence level limits of σ(Υ(5S)→BB̅ )<0.038  nb, σ(Υ(5S)→B^(*)B̅ ^(*)π)<0.055  nb and σ(Υ(5S)→BB̅ ππ)<0.024  nb. We also extract the most precise value of the B_s^* mass to date, M(B_s^*)=(5411.7±1.6±0.6)  MeV/c².

We present the first experimental limits on high-q² contributions to charmless semileptonic B decays of the form expected from the weak annihilation (WA) decay mechanism. Such contributions could bias determinations of |V_ub| from inclusive measurements of B→X_ulν. Using a wide range of models based on available theoretical input we set a limit of Γ_WA/Γ_b→u<7.4% (90% confidence level) on the WA fraction, and assess the impact on previous inclusive determinations of |V_ub|.

We determine the dielectron widths of the Υ(1S), Υ(2S), and Υ(3S) resonances with better than 2% precision by integrating the cross section of e⁺e^-→Υ over the e⁺e^- center-of-mass energy. Using e⁺e^- energy scans of the Υ resonances at the Cornell Electron Storage Ring and measuring Υ production with the CLEO detector, we find dielectron widths of 1.252±0.004(σ_stat)±0.019(σ_syst)  keV, 0.581±0.004±0.009  keV, and 0.413±0.004±0.006  keV for the Υ(1S), Υ(2S), and Υ(3S), respectively.

Using data acquired with the CLEO detector at the CESR e⁺e^- collider at sqrt[s]=3.773  GeV, we measure the cross section for the radiative return process e⁺e^-→γJ/ψ, J/ψ→μ⁺μ^-, resulting in B(J/ψ→μ⁺μ^-)×Γ_ee(J/ψ)=0.3384±0.0058±0.0071  keV, Γ_ee(J/ψ)=5.68±0.11±0.13  keV, and Γ_tot(J/ψ)=95.5±2.4±2.4  keV, in which the errors are statistical and systematic, respectively. We also determine the ratio Γ_ee[ψ(2S)]/Γ_ee(J/ψ)=0.45±0.01±0.02.

Using 281  pb^-1 of data collected with the CLEO-c detector, we report on first observations and measurements of Cabibbo-suppressed decays of D mesons in the following six decay modes: π⁺π^-π⁰π⁰, π⁺π⁺π^-π^-π⁰, π⁺π⁰π⁰, π⁺π⁺π^-π⁰, ηπ⁰, and ωπ⁺π^-. Improved branching fraction measurements in eight other multipion decay modes are also presented. The measured D→ππ rates allow us to extract the ratio of isospin amplitudes A(ΔI=3/2)/A(ΔI=1/2)=0.420±0.014(stat)±0.016(syst) and the strong phase shift of δ_I=(86.4±2.8±3.3)°, which is quite large and now more precisely determined.

Using data obtained with the CLEO III detector, running at the Cornell Electron Storage Ring (CESR), we report on a new study of exclusive radiative Υ(1S) decays into the final states γπ⁺π^-, γK⁺K^-, and γpp̅ . We present branching ratio measurements for the decay modes Υ(1S)→γf₂(1270), Υ(1S)→γf₂^′(1525), and Υ(1S)→γK⁺K^-; helicity production ratios for f₂(1270) and f₂^′(1525); upper limits for the decay Υ(1S)→γf_J(2200), with f_J(2220)→π⁺π^-, K⁺K^-, pp̅ ; and an upper limit for the decay Υ(1S)→γX(1860), with X(1860)→γpp̅ .

We use data collected by the CLEO III detector at the Cornell Electron Storage Ring to measure the inclusive yields of D_s mesons as B(Υ(5S)→D_sX)=(44.7±4.2±9.9)% and B(Υ(4S)→D_sX)=(18.1±0.5±2.8)%. From these measurements, we make a model dependent estimate of the ratio of B_s^(*)B̅ _s^(*) to the total bb̅ quark pair production of (16.0±2.6±5.8)% at the Υ(5S) energy.

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.

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.

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.