Search Results (195 total)

By using 1.8×10⁶ DD̅ pairs, we have measured B(D⁰→π^-e⁺ν_e)=0.299(11)(9)%, B(D⁺→π⁰e⁺ν_e)=0.373(22)(13)%, B(D⁰→K^-e⁺ν_e)=3.56(3)(9)%, and B(D⁺→K̅ ⁰e⁺ν_e)=8.53(13)(23)% and have studied the q² dependence of the form factors. By combining our results with recent lattice calculations, we obtain |V_cd|=0.217(9)(4)(23) and |V_cs|=1.015(10)(11)(106).

Using a sample of 1.8 million DD̅ mesons collected at the ψ(3770) with the CLEO-c detector, we study the semileptonic decays D⁰→π^-e⁺ν_e, D⁺→π⁰e⁺ν_e, D⁰→K^-e⁺ν_e, and D⁺→K̅ ⁰e⁺ν_e. For the total branching fractions we find B(D⁰→π^-e⁺ν_e)=0.299(11)(9)%, B(D⁺→π⁰e⁺ν_e)=0.373(22)(13)%, B(D⁰→K^-e⁺ν_e)=3.56(3)(9)%, and B(D⁺→K̅ ⁰e⁺ν_e)=8.53(13)(23)%, where the first error is statistical and the second systematic. In addition, form factors are studied through fits to the partial branching fractions obtained in five q² ranges. By combining our results with recent unquenched lattice calculations, we obtain |V_cd|=0.217(9)(4)(23) and |V_cs|=1.015(10)(11)(106), where the final error is theoretical.

We present measurements of D→K_S⁰π and D→K_L⁰π branching fractions using 281  pb^-1 of ψ(3770) data at the CLEO-c experiment. We find that B(D⁰→K_S⁰π⁰) is larger than B(D⁰→K_L⁰π⁰), with an asymmetry of R(D⁰)=0.108±0.025±0.024. For B(D⁺→K_S⁰π⁺) and B(D⁺→K_L⁰π⁺), we observe no measurable difference; the asymmetry is R(D⁺)=0.022±0.016±0.018. The D⁰ asymmetry is consistent with the value based on the U-spin prediction A(D⁰→K⁰π⁰)/A(D⁰→K̅ ⁰π⁰)=-tan⁡²θ_C, where θ_C is the Cabibbo angle.

Using 281  pb^-1 of e⁺e^- collisions recorded at the ψ(3770) resonance with the CLEO-c detector at CESR (Cornell Electron Storage Ring), 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⁺)=(3.891±0.035±0.059±0.035)% and B(D⁺→K^-π⁺π⁺)=(9.14±0.10±0.16±0.07)%, where the first uncertainty is statistical, the second is all systematic errors other than final-state radiation (FSR), and the third is the systematic uncertainty due to FSR. We include FSR in these branching fractions by allowing for additional unobserved photons in the final state. Using an independent determination of the integrated luminosity, we also extract the cross sections σ(e⁺e^-→D⁰D̅ ⁰)=(3.66±0.03±0.06)  nb and σ(e⁺e^-→D⁺D^-)=(2.91±0.03±0.05)  nb at a center-of-mass energy, E_cm=3774±1  MeV.

We report on a study of exclusive radiative decays Υ(nS)→γ+R (n=1, 2, 3), with R a narrow resonant hadronic state decaying into four or more charged particles (plus possible neutrals). Using data collected from the CLEO III detector at the Cornell Electron Storage Ring, we present upper limits of order 10^-4 for such bottomonium two-body decays as a function of the mass M_R recoiling opposite the photon.

Using a 281  pb^-1 data sample collected at the ψ(3770) with the CLEO-c detector, we present the first absolute branching fraction measurement of the decay D⁰→K^-π⁺π^-e⁺ν_e at a statistical significance of about 4.0 standard deviations. We find 10 candidates consistent with the decay D⁰→K^-π⁺π^-e⁺ν_e. The probability that a background fluctuation accounts for this signal is less than 4.1×10^-5. We find B(D⁰→K^-π⁺π^-e⁺ν_e)=[2.8_-1.1^+1.4(stat)±0.3(syst)]×10^-4. By restricting the invariant mass of the hadronic system to be consistent with K₁(1270), we obtain the product of branching fractions B(D⁰→K₁^-(1270)e⁺ν_e)×B(K₁^-(1270)→K^-π⁺π^-)=[2.5_-1.0^+1.3(stat)±0.2(syst)]×10^-4. Using B(K₁^-(1270)→K^-π⁺π^-)=(33±3)%, we obtain B(D⁰→K₁^-(1270)e⁺ν_e)=[7.6_-3.0^+4.1(stat)±0.6(syst)±0.7]×10^-4. The last error accounts for the uncertainties in the measured K₁^-(1270)→K^-π⁺π^- branching fractions.

Using the CLEO III detector, we measure absolute cross sections for e⁺e^-→hadrons at seven center-of-mass energies between 6.964 and 10.538 GeV. The values of R, the ratio of hadronic and muon pair production cross sections, are determined within 2% total root-mean-square uncertainty.

We report on a search for the radiative decay of Υ(1S) to the pseudoscalar mesons η and η^′ in (21.2±0.2)×10⁶ Υ(1S) decays collected with the CLEO III detector at the Cornell Electron Storage Ring. The η meson was reconstructed in the three modes η→γγ, η→π⁺π^-π⁰, or η→π⁰π⁰π⁰. The η^′ meson was reconstructed in the mode η^′→π⁺π^-η with η decaying through any of the above three modes, and also η^′→γρ⁰, where ρ⁰→π⁺π^-. Five out of the seven submodes are found to have very low backgrounds. In four of them we find no signal candidates and in one [Υ(1S)→γη^′, η^′→π⁺π^-η, η→π⁺π^-π⁰] there are two good signal candidates, which is insufficient evidence to claim a signal. The other two submodes (η→γγ and η^′→γρ) are background limited, and show no excess of events in their signal regions. We combine the results from different channels and obtain upper limits at the 90% C.L. which are B(Υ(1S)→γη)<1.0×10^-6 and B(Υ(1S)→γη^′)<1.9×10^-6. Our limits are an order of magnitude tighter than the previous ones and below the predictions made by some theoretical models.

We examine e⁺e^-→D_s^-D_s^*+ and D_s^*-D_s⁺ interactions at 4170 MeV using the CLEO-c detector in order to measure the decay constant f_Ds⁺. We use the D_s⁺→ℓ⁺ν channel, where the ℓ⁺ designates either a μ⁺ or a τ⁺, when the τ⁺→π⁺ν̅ . Analyzing both modes independently, we determine B(D_s⁺→μ⁺ν)=(0.594±0.066±0.031)%, and B(D_s⁺→τ⁺ν)=(8.0±1.3±0.4)%. We also analyze them simultaneously to find an effective value of B^eff(D_s⁺→μ⁺ν)=(0.638±0.059±0.033)% and extract f_Ds⁺=274±13±7  MeV. Combining with our previous determination of B(D⁺→μ⁺ν), we also find the ratio f_Ds⁺/f_D⁺=1.23±0.11±0.04. We compare to current theoretical estimates. Finally, we find B(D_s⁺→e⁺ν)<1.3×10^-4 at 90% confidence level.

We present measurements of decay matrix elements for hadronic transitions of the form Υ(nS)→Υ(mS)ππ, where (n,m)=(3,1),(2,1),(3,2). We reconstruct charged and neutral pion modes with the final state Upsilon decaying to either μ⁺μ^- or e⁺e^-. Dalitz plot distributions for the 12 decay modes are fit individually as well as jointly assuming isospin symmetry, thereby measuring the matrix elements of the decay amplitude. We observe and account for the anomaly previously noted in the dipion invariant mass distribution for the Υ(3S)→Υ(1S)ππ transition and obtain good descriptions of the dynamics of the decay using the most general decay amplitude allowed by partial conservation of the axial-vector current considerations. The fits further indicate that the Υ(2S)→Υ(1S)ππ and Υ(3S)→Υ(2S)ππ transitions also show the presence of terms in the decay amplitude that were previously ignored, although at a relatively suppressed level.

We measure the decay constant f_Ds⁺ using the D_s⁺→ℓ⁺ν channel, where the ℓ⁺ designates either a μ⁺ or a τ⁺, when the τ⁺→π⁺ν̅ . Using both measurements we find f_Ds⁺=274±13±7  MeV. Combining with our previous determination of f_D⁺, we compute the ratio f_Ds⁺/f_D⁺=1.23±0.11±0.04. We compare with theoretical estimates.

We have studied semileptonic B decay to the exclusive charmless states π, ρ/ω, η and η^′ using the full 15.5  fb^-1 CLEO Υ(4S) sample, with measurements performed in subregions of phase space to minimize dependence on a priori knowledge of the form factors involved. We find total branching fractions B(B⁰→π^-ℓ⁺ν)=(1.37±0.15_stat±0.11_sys)×10^-4 and B(B⁰→ρ^-ℓ⁺ν)=(2.93±0.37_stat±0.37_sys)×10^-4. We find evidence for B⁺→η^′ℓ⁺ν, with B(B⁺→η^′ℓ⁺ν)=(2.66±±0.80_stat±0.56_sys)×10^-4 and 1.20×10^-4<B(B⁺→η^′ℓ⁺ν)<4.46×10^-4 (90% CL). We also limit B(B⁺→ηℓ⁺ν)<1.01×10^-4 (90% CL). By combining our B→πℓν information with unquenched lattice calculations, we find |V_ub|=(3.6±0.4_stat±0.2_sys-0.4thy^+0.6)×10^-3.

Using e⁺e^-→hadrons data collected with the CLEO-III detector at the Cornell Electron Storage Ring, we study the inclusive production of baryons/antibaryons (p,Λ) and mesons (ϕ and f₂(1270)) in gluon-fragmentation and quark-fragmentation processes. We first corroborate previous per-event total particle yields in Υ(1S)→ggg compared with nearby continuum (e⁺e^-→qq̅ ) indicating greater (∼×2) per-event yields of baryons in 3-gluon fragmentation. We find similar results when we extend that comparison to include the Υ(2S) and Υ(3S) resonances. With higher statistics, we now also probe the momentum dependence of these per-event particle yields. Next, we compare particle production in the photon-tagged process Υ(1S)→ggγ with that in e⁺e^-→qq̅ γ events, to allow comparison of two-parton with three-parton particle-specific fragmentation. For each particle, we determine the “enhancement” ratio, defined as the ratio of particle yields per gluon-fragmentation event compared to quark-fragmentation event. Thus defined, an enhancement of 1.0 implies equal per-event production in gluon and quark fragmentation. In the photon-tagged analysis (Υ(1S)→ggγ compared to e⁺e^-→qq̅ γ), we find almost no enhancement for protons (∼1.2±0.1), but a significant enhancement (∼1.9±0.3) for Λ’s. This small measured proton enhancement rate is supported by a study of baryon production in χ_b2→gg→p+X relative to χ_b1→qq̅ g→p+X. Overall, per-event baryon production in radiative two-gluon fragmentation is somewhat smaller than that observed in three-gluon decays of the Υ(1S). Our results for baryon production are inconsistent with the predictions of the JETSET (7.3) fragmentation model.

We study semileptonic B decay to the exclusive charmless states π, ρ/ω, η, and η^′ using the 16  fb^-1 CLEO Υ(4S) data sample. We find B(B⁰→π^-ℓ⁺ν)=(1.37±0.15_stat±0.11_sys)×10^-4 and B(B⁰→ρ^-ℓ⁺ν)=(2.93±0.37_stat±0.37_sys)×10^-4 and find evidence for B⁺→η^′ℓ⁺ν, with B(B⁺→η^′ℓ⁺ν)=(2.66±0.80_stat±0.56_sys)×10^-4. From our B→πℓν rate for q²>16  GeV² and lattice QCD, we find |V_ub|=(3.6±0.4_stat±0.2_syst-0.4thy^+0.6)×10^-3.

Using 281  pb^-1 of data recorded by the CLEO-c detector in e⁺e^- collisions at the ψ(3770), corresponding to 0.78×10⁶ D⁺D^- pairs, we investigate the substructure of the decay D⁺→π^-π⁺π⁺ using the Dalitz plot technique. We find that our data are consistent with the following intermediate states: ρ(770)π⁺, f₂(1270)π⁺, f₀(1370)π⁺, f₀(1500)π⁺, f₀(980)π⁺, and σπ⁺. We confirm large S wave contributions at low ππ mass. We set upper limits on contributions of other possible intermediate states. We consider three models of the ππ S wave and find that all of them adequately describe our data.