Search Results (504 total)

We present a measurement of the spin-dependent cross sections for the ³He→(e→,e^′)X reaction in the quasielastic and resonance regions at a four-momentum transfer 0.1≤Q²≤0.9  GeV². The spin-structure functions have been extracted and used to evaluate the nuclear Burkhardt-Cottingham and extended Gerasimov-Drell-Hearn sum rules for the first time. The data are also compared to an impulse approximation calculation and an exact three-body Faddeev calculation in the quasielastic region.

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 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.

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.

We report a generalized scenario for the formation of modulated smectic phases of bent-core molecules based on locally ferroelectric layering and spontaneous splay of the polarization. Twelve phases are proposed, distinguished by neighboring splay stripes with either syn- or antiorder of the polarization and undulation slope, in addition to layer continuity versus layer discontinuity at the intervening defects. We outline the experimental techniques necessary to differentiate among the phases and interpret previous results in the present context, using high resolution x-ray scattering diffraction and block and undulation models of the layer organization to distinguish among the three 2D lattice types which emerge.

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 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.

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.