Search Results (1,029 total)

We report measurements of the exclusive cross section for e⁺e^-→D⁰D^*-π⁺ as a function of center-of-mass energy from the D⁰D^*-π⁺ threshold to 5.2 GeV with initial-state radiation. No evidence is found for Y(4260)→D⁰D^*-π⁺ decays. The analysis is based on a data sample collected with the Belle detector at or near a center-of-mass energy of 10.58 GeV with an integrated luminosity of 695  fb^-1 at the KEKB asymmetric-energy e⁺e^- collider.

We demonstrate experimentally the efficient fusion neutron generation from Coulomb explosion (CE) of laser irradiated large-size heteronuclear deuterated methane clusters. A conversion efficiency of 2.1×10⁶ neutrons/J of incident laser energy is obtained with a 120 mJ, 70 fs laser pulse. It is 50 times higher than that of homonuclear deuterium clusters of similar size. This enhancement is attributed to the significant increase in the deuteron kinetic energies by fourfold due to energetic boosting and overrun effects during CE of heteronuclear clusters. The yield of 5.5×10⁶ neutrons per pulse is obtained with a 100 TW, 50 fs driving laser pulse at an intensity of 1.5×10¹⁹ W/cm². This work may facilitate the development of a high-flux table-top neutron source.

Realistic three-dimensional atomistic structures of Zr_xCu_100−x (x=35,50) bulk metallic glasses are constructed using a combination of x-ray diffraction experiment and computational modeling. A cluster correlation method is developed to analyze the medium-range order in amorphous systems. We show that the glass systems consist of a stringlike backbone network formed by icosahedral clusters and a liquidlike structure filling in the remaining space. These findings are consistent with those obtained from our independent classical molecular-dynamics studies with embedded-atom method potential for ZrCu system. Such a heterogeneous structure provides a fundamental structural perspective of dynamical heterogeneity and glass formation.

We study the existence and stability of localized modes in the two-dimensional (2D) nonlinear Schrödinger/Gross-Pitaevskii (NLS/GP) equation with a symmetric four-well potential. Using the corresponding four-mode approximation, we trace the parametric evolution of the trapped stationary modes, starting from the linear limit, and thus derive a complete bifurcation diagram for families of the stationary modes. This provides the picture of spontaneous symmetry breaking in the fundamental 2D setting. In a broad parameter region, the predictions based on the four-mode decomposition are found to be in good agreement with full numerical solutions of the NLS/GP equation. Stability properties of the stationary states coincide with those suggested by the corresponding discrete model in the large-amplitude limit. The dynamics of unstable modes is explored by means of direct simulations. Finally, in addition to the full analysis for the case of the self-attractive nonlinearity, the bifurcation diagram for the case of self-repulsion is briefly considered too.

Wrinkling was observed for a circular monolayer graphene sheet in nanoindentation based on molecular-dynamics simulations. The mechanics fundamentals of this phenomenon were then explored using a two-dimensional plate model. It was found that the graphene wrinkles when the indentation depth reaches a critical value, the wrinkling is induced by the circumferential compression in the graphene, and the bending stiffness of the graphene sheet plays an essential role in stabilizing its one-atom layer nanostructures. It was shown that bending stiffness and in-plane stiffness are key indicators that signify the intrinsic mechanical properties of a graphene.

We study B→K^(*)ℓ⁺ℓ^- decays (ℓ=e, μ) based on a data sample of 657×10⁶ BB̅ pairs collected with the Belle detector at the KEKB e⁺e^- collider. We report the differential branching fraction, isospin asymmetry, K^* polarization, and the forward-backward asymmetry (A_FB) as functions of q²=M_ℓℓ²c². The fitted A_FB spectrum exceeds the standard model expectation by 2.7 standard deviations. The measured branching fractions are B(B→K^*ℓ⁺ℓ^-)=(10.7_-1.0^+1.1±0.9)×10^-7 and B(B→Kℓ⁺ℓ^-)=(4.8_-0.4^+0.5±0.3)×10^-7, where the first errors are statistical and the second are systematic, with the muon to electron ratios R_K^*=0.83±0.17±0.08 and R_K=1.03±0.19±0.06.

Using molecular dynamics simulation, we show direct evidence of the unexpected phenomenon of “water that does not wet a water monolayer” at room temperature. This phenomenon is attributed to the structure of the water beneath the water droplet, which exhibits an ordered water monolayer. Remarkably, there remains a considerable number of dangling OH bonds in this room temperature water monolayer, in contrast with the absence of dangling OH bonds at cryogenic temperature.

We present a measurement of the D⁰-D̅ ⁰ mixing parameter y_CP using a flavor-untagged sample of D⁰→K_S⁰K⁺K^- decays. The measurement is based on a 673  fb^-1 data sample recorded with the Belle detector at the KEKB asymmetric-energy e⁺e^- collider. Using a method based on measuring the mean decay time for different K⁺K^- invariant mass intervals, we find y_CP=(+0.11±0.61(stat.)±0.52(syst.))%.

The nonresonant component of radiative neutron capture reactions is parametrized at low energies by a polynomial of second degree. The potential model is first used to reproduce experimental data below 1 MeV with the help of spectroscopic factors. The fits are found sensitive to the scattering length of the initial s or p waves. The coefficients of a Taylor expansion are then calculated by resolution of the Schrödinger equation and its energy derivatives at energy zero. Such theory-guided parametrizations are derived for neutron capture by ⁷Li, ¹²C, ¹⁴C, ¹⁶O, and ¹⁸O. When the capture proceeds from the s wave to a weakly bound state, a Padé-like parametrization better approximates the potential-model results.

We report a measurement of the exclusive B⁺ meson decay to the D_s^(*)-K⁺π⁺ final state using 657×10⁶BB̅ pairs collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e⁺e^- collider. We use D_s^*-→D_s^-γ and the D_s^-→ϕπ^-, K̅ ^*(892)⁰K^- and K_S⁰K^- decay modes for D_s^(*) reconstruction and measure the following branching fractions: B(B⁺→D_s^-K⁺π⁺)=(1.71_-0.07^+0.08(stat)_-0.20^+0.20(syst)±0.15(B_int))×10^-4 and B(B⁺→D_s^*-K⁺π⁺)=(1.31_-0.12^+0.13(stat)_-0.25^+0.25(syst)±0.12(B_int))×10^-4. The uncertainties are due to statistics, experimental systematic errors, and uncertainties of intermediate branching fractions, respectively.

The passage of a free-electron beam through a nanohole in a periodically layered metal-dielectric structure creates a new type of tunable, nanoscale radiation source—a “light well”. In the reported demonstration, tunable light is generated at an intensity of ∼200  W/cm² as electrons with energies in the 20–40 keV range are injected into gold-silica well structures with a lateral size of just a few hundred nanometers.

We report measurements of charmless hadronic B⁰ decays into the π⁺π^-K⁺π^- final state. The analysis uses a sample of 657×10⁶ BB̅ pairs collected with the Belle detector at the KEKB asymmetric-energy e⁺e^- collider at the resonance. The decay B⁰→ρ⁰K⁺π^- is observed for the first time; the significance is 5.0σ and the corresponding partial branching fraction for M_Kπ∈(0.75,1.20)  GeV/c² is [2.8±0.5(stat)±0.5(syst)]×10^-6. We also obtain the first evidence for B⁰→f₀(980)K⁺π^- with 3.5σ significance and for B⁰→π⁺π^-K^*0 with 4.5σ significance. For the two-body decays B⁰→ρ⁰K^*0 and B⁰→f₀(980)K^*0, the significances are 2.7σ and 2.5σ, respectively, and the upper limits on the branching fractions are 3.4×10^-6 and 2.2×10^-6 at 90% confidence level.

The differential cross section for the process γγ→ηπ⁰ has been measured in the kinematic range 0.84  GeV<W<4.0  GeV, |cos⁡θ^*|<0.8, where W and θ^* are the energy and π⁰ (or η) scattering angle, respectively, in the γγ center-of-mass system. The results are based on a 223  fb^-1 data sample collected with the Belle detector at the KEKB e⁺e^- collider. Clear peaks due to the a₀(980) and a₂(1320) are visible. The differential cross sections are fitted in the energy region 0.9  GeV<W<1.46  GeV to obtain the parameters of the a₀(980). Its mass, width and Γ_γγB(ηπ⁰) are measured to be 982.3_-0.7-4.7^+0.6+3.1  MeV/c², 75.6±1.6_-10.0^+17.4  MeV and 128_-2-43⁺³⁺⁵⁰²  eV, respectively. The energy and angular dependences above 3.1 GeV are compared with those measured in the π⁰π⁰ channel. The integrated cross section over |cos⁡θ^*|<0.8 has a W^-n dependence with n=10.5±1.2±0.5, which is slightly larger than that for π⁰π⁰. The differential cross sections show a sin⁡^-4θ^* dependence similar to γγ→π⁰π⁰. The measured cross section ratio, σ(ηπ⁰)/σ(π⁰π⁰)=0.48±0.05±0.04, is consistent with a QCD-based prediction.

From a Dalitz plot analysis of B→Kπ⁺ψ^′ decays, we find a signal for Z(4430)⁺→π⁺ψ^′ with a mass M=(4443_-12-13⁺¹⁵⁺¹⁹)  MeV/c², width Γ=(107_-43-56⁺⁸⁶⁺⁷⁴)  MeV, product branching fraction B(B̅ ⁰→K^-Z(4430)⁺)×B(Z(4430)⁺→π⁺ψ^′)=(3.2_-0.9-1.6^+1.8+5.3)×10^-5, and significance of 6.4σ that agrees with previous Belle measurements based on the same data sample. In addition, we determine the branching fraction B(B⁰→K^*(892)⁰ψ^′)=(5.52_-0.32-0.58^+0.35+0.53)×10^-4 and the fraction of K^*(892)⁰ mesons that are longitudinally polarized f_L=(44.8_-2.7-5.3^+4.0+4.0)%. These results are obtained from a 605  fb^-1 data sample that contains 657×10⁶ BB̅ pairs collected near the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e⁺e^- collider.

The cross sections for e⁺e^-→ϕπ⁺π^- and e⁺e^-→ϕf₀(980) are measured from threshold to sqrt[s]=3.0  GeV using initial-state radiation. The analysis is based on a data sample of 673  fb^-1 collected on and below the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e⁺e^- collider. First measurements are reported for the resonance parameters of the ϕ(1680) in the ϕπ⁺π^- mode: m=(1689±7±10)  MeV/c² and Γ=(211±14±19)  MeV/c². A structure at sqrt[s]=2.1  GeV/c², corresponding to the so called Y(2175), is observed; its mass and width are determined to be (2079±13_-28⁺⁷⁹)  MeV/c² and (192±23_-61⁺²⁵)  MeV/c², respectively.

We present in this work a theoretical framework based on the tight-binding method, which is able to probe at a local atomic level the optoelectronic response of nanomaterial systems and link it to the associated disorder. We apply this methodology to carbon nanocomposites containing diamond nanocrystals. We find that significant structural and topological disorder exists at the interface between the nanodiamonds and the embedding amorphous carbon matrix. This can be quantitatively probed by extracting the Urbach energies from the optical parameters. Disorder in the nanocrystals appears in their outer shell near the interface and is manifested as bond length and angle distortions. Energetics and stability analysis show that nanodiamonds embedded in matrices with high density and high fraction of fourfold coordinated atoms are more stable.

Photoproduction of Λ(1520) with liquid hydrogen and deuterium targets was examined at photon energies below 2.4 GeV in the SPring-8 LEPS experiment. For the first time, the differential cross sections were measured at low energies and with a deuterium target. A large asymmetry of the production cross sections from protons and neutrons was observed at backward K^+/0 angles. This suggests the importance of the contact term, which coexists with t-channel K exchange under gauge invariance. This interpretation was compatible with the differential cross sections, decay asymmetry, and photon beam asymmetry measured in the production from protons at forward K⁺ angles.

We use spin-transfer-driven ferromagnetic resonance (ST-FMR) to measure the spin-transfer torque vector τ in MgO-based magnetic tunnel junctions as a function of the offset angle between the magnetic moments of the electrodes and as a function of bias, V. We explain the conflicting conclusions of two previous experiments by accounting for additional terms that contribute to the ST-FMR signal at large |V|. Including the additional terms gives us improved precision in the determination of τ(V), allowing us to distinguish among competing predictions. We determine that the in-plane component of dτ/dV has a weak but nonzero dependence on bias, varying by 30%–35% over the bias range where the measurements are accurate, and that the perpendicular component can be large enough to be technologically significant. We also make comparisons to other experimental techniques that have been used to try to measure τ(V).

We report the first observation of the doubly Cabibbo-suppressed decay D_s⁺→K⁺K⁺π^- using 605  fb^-1 of data collected with the Belle detector at the KEKB asymmetric-energy e⁺e^- collider. The branching ratio with respect to its Cabibbo-favored counterpart B(D_s⁺→K⁺K⁺π^-)/B(D_s⁺→K⁺K^-π⁺) is (0.229±0.028±0.012)%, where the first uncertainty is statistical and the second is systematic. We also report a significantly improved measurement of the doubly Cabibbo-suppressed decay D⁺→K⁺π⁺π^-, with a branching ratio B(D⁺→K⁺π⁺π^-)/B(D⁺→K^-π⁺π⁺)=(0.569±0.018±0.014)%.

The bulk and surface electronic structure of In₂O₃ has proved controversial, prompting the current combined experimental and theoretical investigation. The band gap of single-crystalline In₂O₃ is determined as 2.93±0.15 and 3.02±0.15 eV for the cubic bixbyite and rhombohedral polymorphs, respectively. The valence-band density of states is investigated from x-ray photoemission spectroscopy measurements and density-functional theory calculations. These show excellent agreement, supporting the absence of any significant indirect nature of the In₂O₃ band gap. Clear experimental evidence for an s-d coupling between In 4d and O 2s derived states is also observed. Electron accumulation, recently reported at the (001) surface of bixbyite material, is also shown to be present at the bixbyite (111) surface and the (0001) surface of rhombohedral In₂O₃.

We have studied Ni-substitution effect in LaFe_1−xNi_xAsO (0≤x≤0.1) by the measurements of x-ray diffraction, electrical resistivity, magnetic susceptibility, and heat capacity. The nickel doping drastically suppresses the resistivity anomaly associated with spin-density-wave ordering in the parent compound. Superconductivity emerges in a narrow region of 0.03≤x≤0.06 with the maximum T_c of 6.5 K at x=0.04, where enhanced magnetic susceptibility shows up. The upper critical field at zero temperature is estimated to exceed the Pauli paramagnetic limit. The much lowered T_c in comparison with LaFeAsO_1−xF_x system is discussed.

We propose an efficient scheme to simulate noncontact atomic force microscopy images by using first-principles self-consistent potential from the sample as input without explicit modeling of the atomic force microscopy tip. Our method is applied to various types of semiconductor surfaces including Si(111)-(7×7), TiO₂(110)-(1×1), Ag/Si(111)-(sqrt[3]×sqrt[3])R30°, and Ge/Si(105)-(1×2) surfaces. We obtain good agreement with experimental results and previous theoretical studies, and our method can aid in identifying different structural models for surface reconstruction.

In their comment [X. F. Sun and Yoichi Ando, preceding paper, Phys. Rev. B79, 176501 (2009)] on our study of phonon heat transport in Nd₂CuO₄ [S. Y. Li, J.-B. Bonnemaison, A. Payeur, P. Fournier, C. H. Wang, X. H. Chen, and Louis Taillefer, Phys. Rev. B 77, 134501 (2008)], Sun and Ando estimate that the phonon mean free path at low temperature is roughly half the width of the single crystal used in our study, from which they argue that phonon scattering cannot be dominated by sample boundaries. Here we show that their use of specific-heat data on Nd₂CuO₄, which contains a large magnetic contribution at low temperature that is difficult to reliably extract, leads to an underestimate of the mean free path by a factor 2 compared to an estimate based on the specific-heat data of the nonmagnetic isostructural analog Pr₂CuO₄. This removes the apparent contradiction raised by Sun and Ando.

We report on a search for the X(1812) state in the decay B^±→K^±ωϕ with a data sample of 657×10⁶ BB̅ pairs collected with the Belle detector at the KEKB e⁺e^- collider. No significant signal is observed. An upper limit B(B^±→K^±X(1812),X(1812)→ωϕ)<3.2×10^-7 (90% C.L.) is determined. We also constrain the three-body decay branching fraction to be B(B^±→K^±ωϕ)<1.9×10^-6 (90% C.L.).