Search Results (191 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 exploit the quantum coherence between pair-produced D⁰ and D̅ ⁰ in ψ(3770) decays to study charm mixing, which is characterized by the parameters x and y, and to make a first determination of the relative strong phase δ between D⁰→K⁺π^- and D̅ ⁰→K⁺π^-. Using 281  pb^-1 of e⁺e^- collision data collected with the CLEO-c detector at E_cm=3.77  GeV, as well as branching fraction input and time-integrated measurements of R_M≡(x²+y²)/2 and R_WS≡Γ(D⁰→K⁺π^-)/Γ(D̅ ⁰→K⁺π^-) from other experiments, we find cos⁡δ=1.03_-0.17^+0.31±0.06, where the uncertainties are statistical and systematic, respectively. By further including other mixing parameter measurements, we obtain an alternate measurement of cos⁡δ=1.10±0.35±0.07, as well as xsin⁡δ=(4.4_-1.8^+2.7±2.9)×10^-3 and δ=(22_-12-11⁺¹¹⁺⁹)°.

Using 281  pb^-1 of data collected with the CLEO-c detector, we present new measurements of Cabibbo-suppressed decays of D⁰ and D⁺ mesons to η and η^′ final states. We make first observations of D⁰→η^′π⁰, ηη, ηη^′, and ηπ⁺π^-, and find evidence for D⁺→ηπ⁺π⁰, D⁺→η^′π⁺π⁰, and D⁰→η^′π⁺π^-. We also report on improved measurements of D⁰→ηπ⁰, D⁺→ηπ⁺, and D⁺→η^′π⁺. Using the measured two-body Cabibbo-suppressed decays, we extract amplitudes for specific flavor topologies and compare them to those from Cabibbo-favored decays.

Using 281  pb^-1 of data collected with the CLEO-c detector at the ψ(3770) resonance, we have studied Cabibbo-suppressed decays of D mesons to final states with two kaons. We present results for the absolute branching fractions of the modes D⁰→K⁺K^-, D⁰→K_S⁰K_S⁰, and D⁺→K⁺K_S⁰. We measure B(D⁰→K⁺K^-)=(4.08±0.08±0.09)×10^-3, B(D⁰→K_S⁰K_S⁰)=(1.46±0.32±0.09)×10^-4, and B(D⁺→K⁺K_S⁰)=(3.14±0.09±0.08)×10^-3. We also determine the ratio B(D⁰→K⁺K^-)/B(D⁰→π⁺π^-)=2.89±0.05±0.06. For each measurement, the first uncertainty is statistical and the second uncertainty is systematic.

Using e⁺e^-→D_s^*-D_s⁺ data collected near the peak D_s production energy, E_cm=4170  MeV, with the CLEO-c detector, we present the first observation of the decay D_s⁺→pn̅ . We measure a branching fraction B(D_s⁺→pn̅ )=(1.30±0.36_-0.16^+0.12)×10^-3. This is the first observation of a charmed meson decaying into a baryon-antibaryon final state.

The branching fractions of D_s^± meson decays serve to normalize many measurements of processes involving charm quarks. Using 298  pb^-1 of e⁺e^- collisions recorded at a center of mass energy of 4.17 GeV, we determine absolute branching fractions for eight D_s^± decays with a double tag technique. In particular we determine the branching fraction B(D_s⁺→K^-K⁺π⁺)=(5.50±0.23±0.16)%, where the uncertainties are statistical and systematic, respectively. We also provide partial branching fractions for kinematic subsets of the K^-K⁺π⁺ decay mode.

Using a sample of tagged D_s⁺ decays collected near the D_s^*±D_s^∓ peak production energy in e⁺e^- collisions with the CLEO-c detector, we study the leptonic decay D_s⁺→τ⁺ν_τ via the decay channel τ⁺→e⁺ν_eν̅ _τ. We measure B(D_s⁺→τ⁺ν_τ)=(6.17±0.71±0.34)%, where the first error is statistical and the second systematic. Combining this result with our measurements of D_s⁺→μ⁺ν_μ and D_s⁺→τ⁺ν_τ (via τ⁺→π⁺ν̅ _τ), we determine f_Ds=(274±10±5)  MeV.

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.

The exclusive electroproduction process e→p→e^'nπ⁺ was measured in the range of the photon virtuality Q²=1.7-4.5 GeV², and the invariant mass range for the nπ⁺ system of W=1.15-1.7 GeV using the CEBAF Large Acceptance Spectrometer. For the first time, these kinematics are probed in exclusive π⁺ production from protons with nearly full coverage in the azimuthal and polar angles of the nπ⁺ center-of-mass system. The nπ⁺ channel has particular sensitivity to the isospin ½ excited nucleon states, and together with the pπ⁰ final state will serve to determine the transition form factors of a large number of resonances. The largest discrepancy between these results and present modes was seen in the σ_LT^' structure function. In this experiment, 31,295 cross section and 4,184 asymmetry data points were measured. Because of the large volume of data, only a reduced set of structure functions and Legendre polynomial moments can be presented that are obtained in model-independent fits to the differential cross sections.

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.

The photoproduction of vector mesons on various nuclei has been studied using the CLAS detector at Jefferson Laboratory. The vector mesons, ρ, ω, and ϕ, are observed via their decay to e⁺e^-, in order to reduce the effects of final-state interactions in the nucleus. Of particular interest are possible in-medium effects on the properties of the ρ meson. The ρ mass spectrum is extracted from the data on various nuclei, ²H, C, Fe, and Ti. We observe no significant mass shift and some broadening consistent with expected collisional broadening for the ρ meson.

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.

The cross section and decay angular distributions for the coherent ϕ-meson photoproduction on the deuteron have been measured for the first time up to a squared four-momentum transfer t=(p_γ-p_ϕ)²=-2 GeV²/c², using the CLAS detector at the Thomas Jefferson National Accelerator Facility. The cross sections are compared with predictions from a rescattering model. In a framework of vector meson dominance, the data are consistent with the total ϕ-N cross section σ_ϕN at about 10 mb. If vector meson dominance is violated, a larger σ_ϕN is possible by introducing a larger t slope for the ϕN→ϕN process than that for the γN→ϕN process. The decay angular distributions of the ϕ are consistent with helicity conservation.

Using data collected near the D_s^*+D_s^- peak production energy E_cm=4170  MeV by the CLEO-c detector, we study the decays of D_s⁺ mesons to two pseudoscalar mesons. We report on searches for the singly Cabibbo-suppressed D_s⁺ decay modes K⁺η, K⁺η^′, π⁺K_S⁰, K⁺π⁰, and the isospin-forbidden decay mode D_s⁺→π⁺π⁰. We normalize with respect to the Cabibbo-favored D_s⁺ modes π⁺η, π⁺η^′, and K⁺K_S⁰, and obtain ratios of branching fractions: B(D_s⁺→K⁺η)/B(D_s⁺→π⁺η)=(8.9±1.5±0.4)%, B(D_s⁺→K⁺η^′)/B(D_s⁺→π⁺η^′)=(4.2±1.3±0.3)%, B(D_s⁺→π⁺K_S⁰)/B(D_s⁺→K⁺K_S⁰)=(8.2±0.9±0.2)%, B(D_s⁺→K⁺π⁰)/B(D_s⁺→K⁺K_S⁰)=(5.5±1.3±0.7)%, and B(D_s⁺→π⁺π⁰)/B(D_s⁺→K⁺K_S⁰)<4.1% at 90% C.L., where the uncertainties are statistical and systematic, respectively.

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 mass of the η meson using ψ(2S)→ηJ/ψ events acquired with the CLEO-c detector operating at the CESR e⁺e^- collider. Using the four decay modes η→γγ, 3π⁰, π⁺π^-π⁰, and π⁺π^-γ, we find M_η=547.785±0.017±0.057  MeV, in which the first uncertainty is statistical and the second systematic. This result has an uncertainty comparable to the two most precise previous measurements and is consistent with that of NA48, but is inconsistent at the level of 6.5σ with the much smaller mass obtained by GEM.

The decay ψ(2S)→ηJ/ψ is used to measure, for the first time, all prominent η-meson branching fractions with the same experiment in the same dataset, thereby providing a consistent treatment of systematics across branching fractions. We present results for η decays to γγ, π⁺π^-π⁰, 3π⁰, π⁺π^-γ and e⁺e^-γ, accounting for 99.9% of all η decays. The precision of several of the branching fractions and their ratios is improved. Two channels, π⁺π^-γ and e⁺e^-γ, show results that differ at the level of three standard deviations from those previously determined.