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Li, Y.

Publications and source records attributed to Li, Y..

At least 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Measurement of the decay B → D ℓ ν ℓ in fully reconstructed events and determination of the Cabibbo-Kobayashi-Maskawa matrix element | V c b |

We present a determination of the magnitude of the Cabibbo-Kobayashi-Maskawa matrix element |Vcb| using the decay B → Dℓν ℓ (ℓ = e,μ) based on 711 fb –1 of e + e – → Υ(4S) data recorded by the Belle detector and containing 772 × 10 6 BB¯ pairs. Here, one B meson in the event is fully reconstructed in a hadronic decay mode, while the other, on the signal side, is partially reconstructed from a charged lepton and either a D + or D 0 meson in a total of 23 hadronic decay modes. The isospin-averaged branching fraction of the decay B → Dℓν ℓ is found to be B(B 0 → D – ℓ + ν ℓ ) = (2.31 ± 0.03(stat) ± 0.11(syst))%. Analyzing the differential decay rate as a function of the hadronic recoil with the parametrization of Caprini, Lellouch, and Neubert and using the form-factor prediction G(1) = 1.0541 ± 0.0083 calculated by FNAL/MILC, we obtain η EW |V cb | = (40.12 ± 1.34) × 10 –3 , where ηEW is the electroweak correction factor. Alternatively, assuming the model-independent form-factor parametrization of Boyd, Grinstein, and Lebed and using lattice QCD data from the FNAL/MILC and HPQCD collaborations, we find η EW |V cb | = (41.10 ± 1.14) × 10 –3 .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

First observation of the decay B 0 → ψ ( 2 S ) π 0

We report a measurement of the B 0 → ψ(2S)π 0 branching fraction based on the full Υ(4S) data set of 772 × 10 6 BB¯ pairs collected by the Belle detector at the KEKB asymmetric-energy e + e – collider. We obtain B(B 0 → ψ(2S)π 0 ) = (1.17 ± 0.17(stat) ± 0.08(syst)) × 10 –5 . Here, the result has a significance of 7.2 standard deviations and is the first observation of the decay B 0 → ψ(2S)π 0 .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Search for B 0 → π – τ + ν τ with hadronic tagging at Belle

We search for the process B 0 → π – τ + ν τ using the full Belle data set of 711 fb –1 , corresponding to 772 × 10 6 BB¯ pairs, collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e + e – collider. Here, we reconstruct one B meson in a hadronic decay and search for the B 0 → π – τ + ν τ process in the remainder of the event. No significant signal is observed and an upper limit of B(B 0 → π – τ + ν τ ) < 2.5 × 10 –4 is obtained at the 90% confidence level.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Study of π 0 pair production in single-tag two-photon collisions

We report a measurement of the differential cross section of π 0 pair production in single-tag two-photon collisions, γ*γ→π 0 π 0 , in e + e - scattering. The cross section is measured for Q 2 up to 30 GeV 2 , where Q 2 is the negative of the invariant mass squared of the tagged photon, in the kinematic range 0.5 GeV < W < 2.1 GeV and |cosθ*| < 1.0 for the total energy and pion scattering angle, respectively, in the γ*γ center-of-mass system. The results are based on a data sample of 759 fb -1 collected with the Belle detector at the KEKB asymmetric-energy e + e - collider. The transition form factor of the f 0 (980) and that of the f 2 (1270) with the helicity-0, -1, and -2 components separately are measured for the first time and are compared with theoretical calculations.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

A conductive scanning study of La{sub 0.67}Sr{sub 0.33}MnO{sub 3}/Nb:SrTiO{sub 3} hetero-junction

Basing on conductive atomic force microscopy, we presented a direct conductance mapping for the interface of the La{sub 0.67}Sr{sub 0.33}MnO{sub 3}/Nb:SrTiO{sub 3} hetero-junction. The most remarkable observation is the presence of an interfacial layer in Nb:SrTiO{sub 3} adjacent to the manganite film. Within this layer, the AFM tip/Nb:SrTiO{sub 3} contact shows a current-voltage dependence that strongly deviates from Shockley equation, unlike a Schottky diode. Spatial extension of this layer is explored and possible transport mechanism in or outside this interfacial layer is discussed. The present work gives a direct intuitional image on the interface of manganite junction. The principle proven here can be extended to other complex oxide interfaces.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Measurement of the lepton forward-backward asymmetry in B → X s ℓ + ℓ - decays with a sum of exclusive modes

We report the first measurement of the lepton forward-backward asymmetry $\mathscr{A}$ FB as a function of the squared four-momentum of the dilepton system, q 2 , for the electroweak penguin process B→X s ℓ + ℓ - with a sum of exclusive final states, where ℓ is an electron or a muon and X s is a hadronic recoil system with an s quark. The results are based on a data sample containing 772×10 6 $B$$\bar{B}$ pairs recorded at the Υ(4S) resonance with the Belle detector at the KEKB e + e - collider. $\mathscr{A}4 FB for the inclusive B→X s ℓ + ℓ - is extrapolated from the sum of 10 exclusive X s states whose invariant mass is less than 2 GeV/c 2 . For q 2 >10.2 GeV 2 /c 2 , $\mathscr{A}$ FB <0 is excluded at the 2.3σ level, where σ is the standard deviation. For q 2 <4.3 GeV 2 /c 2 , the result is within 1.8σ of the Standard Model theoretical expectation.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Measurements of the Υ ( 10860 ) and Υ ( 11020 ) resonances via σ ( e + e - → Υ ( n S ) π + π - )

In this work, we report new measurements of the total cross sections for e + e - → Υ ( n S ) π + π - ( n = 1 , 2, 3) and e + e - → b b ¯ from a high-luminosity fine scan of the region s = 10.63 – 11.05 GeV with the Belle detector. We observe that the Υ ( n S ) π + π - spectra have little or no nonresonant component and extract from them the masses and widths of Υ ( 10860 ) and Υ ( 11020 ) and their relative phase. We find M 10860 = ( 10891.1 ± 3. 2 - 1.7 + 0.6 ) MeV / c 2 and Γ 10860 = ( 53. 7 - 5.6 - 5.4 + 7.1 + 1.3 ) MeV and report first measurements M 11020 = ( 10987. 5 - 2.5 - 2.1 + 6.4 + 9.0 ) MeV / c 2 , Γ 11020 = ( 6 1 - 19 - 20 + 9 + 2 ) MeV , and Φ 11020 - Φ 10860 = ( - 1.0 ± 0.4 - 0.1 + 1.4 ) rad .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS2016

WRF-Chem Simulations of Lightning-NOx Production and Transport in Oklahoma and Colorado Thunderstorms Observed During DC3

The focus of this analysis is on lightning-generated nitrogen oxides (LNOx) and their distribution for two thunderstorms observed during the Deep Convective Clouds and Chemistry (DC3) field campaign in May-June 2012. The Weather Research and Forecasting Chemistry (WRF-Chem) model is used to perform cloud-resolved simulations for the May 29-30 Oklahoma severe convection, which contained one supercell, and the June 6-7 Colorado squall line. Aircraft and ground-based observations (e.g., trace gases, lightning and radar) collected during DC3 are used in comparisons against the model-simulated lightning flashes generated by the flash rate parameterization schemes (FRPSs) incorporated into the model, as well as the model-simulated LNOx predicted in the anvil outflow. Newly generated FRPSs based on DC3 radar observations and Lightning Mapping Array data are implemented in the model, along with previously developed schemes from the literature. The results of these analyses will also be compared between storms to investigate which FRPSs were most appropriate for the two types of convection and to examine the variation in the LNOx production. The simulated LNOx results from WRF-Chem will also be compared against other previously studied mid-latitude thunderstorms.

Lightning↗
DOE OSTI2015

Toward complete spectroscopy of 167 Lu

Excited states in 167 Lu were populated in the 123 Sb( 48 Ca,4n) reaction at 203 MeV and decay γ rays measured using the Gammasphere spectrometer array. Two triaxial strongly deformed bands were identified previously and interpreted as zero- and one-phonon wobbling excitations. As a result of more extensive band search, the level scheme has been considerably extended to include ten new rotational bands and some 630γ-ray transitions. A number of interband linking transitions were revealed, so that all but two bands could be connected with each other. Configurations are proposed for all new bands based on measured observables, with the help of cranked shell model calculations. A γ-ray sequence, previously suggested as a triaxial strongly deformed band based on quasiparticle excitations coexisting with the wobbling excitation in the triaxial potential well, has now been determined to be a signature partner of a coupled band, associated with a normal deformed five-quasiparticle configuration. Here, the possibility of two new bands being associated with triaxial deformation is discussed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

The effects of insulating coatings and current prepulse on tungsten planar wire array Z-pinches

This paper presents experimental results on the effects of insulating coatings and current prepulse on tungsten planar wire array Z-pinches on ∼100 ns main current facility. Optical framing images indicated that without a current prepulse the wire ablation process was asymmetrical and the implosion was zippered. The x-ray peak power was ∼320 GW. By using insulating coatings on the wire surface the asymmetry remained, and the processes of ablation and implosion were delayed by ∼30 ns. The x-ray burst was narrow and decreased to ∼200 GW. When current prepulses were used on both standard and insulated wire arrays, implosion symmetry was improved and the x-ray burst was improved (to ∼520 GW peak power). In addition, there was a strong emitting precursor column for insulated loads with the current prepulse.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Monoclinic crystal structure of α - RuCl 3 and the zigzag antiferromagnetic ground state

We have proposed the layered honeycomb magnet α - RuCl 3 as a candidate to realize a Kitaev spin model with strongly frustrated, bond-dependent, anisotropic interactions between spin-orbit entangled j eff = 1/2 Ru 3 + magnetic moments. We report a detailed study of the three-dimensional crystal structure using x-ray diffraction on untwinned crystals combined with structural relaxation calculations. We consider several models for the stacking of honeycomb layers and find evidence for a parent crystal structure with a monoclinic unit cell corresponding to a stacking of layers with a unidirectional in-plane offset, with occasional in-plane sliding stacking faults, in contrast with the currently assumed trigonal three-layer stacking periodicity. We also report electronic band-structure calculations for the monoclinic structure, which find support for the applicability of the j eff = 1/2 picture once spin-orbit coupling and electron correlations are included. Of the three nearest-neighbor Ru-Ru bonds that comprise the honeycomb lattice, the monoclinic structure makes the bond parallel to the b axis nonequivalent to the other two, and we propose that the resulting differences in the magnitude of the anisotropic exchange along these bonds could provide a natural mechanism to explain the previously reported spin gap in powder inelastic neutron scattering measurements, in contrast to spin models based on the three-fold symmetric trigonal structure, which predict a gapless spectrum within linear spin wave theory. Our susceptibility measurements on both powders and stacked crystals, as well as magnetic neutron powder diffraction, show a single magnetic transition upon cooling below T N ≈ 13 K. Our analysis of our neutron powder diffraction data provides evidence for zigzag magnetic order in the honeycomb layers with an antiferromagnetic stacking between layers. Magnetization measurements on stacked single crystals in pulsed field up to 60 T show a single transition around 8 T for in-plane fields followed by a gradual, asymptotic approach to magnetization saturation, as characteristic of strongly anisotropic exchange interactions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Observation of B 0 → p Λ ¯ D ( * ) -

We report the first observation of the decays B 0 →p$\bar{Λ}$D(*)-. The data sample of 711 fb -1 used in this analysis corresponds to 772 million $B$$\bar{B}$ pairs, collected at the Υ(4S) resonance by the Belle detector at the KEKB asymmetric-energy e + e - collider. We observe 19.8σ and 10.8σ excesses of events for the two decay modes and measure the branching fractions of B 0 →p$\bar{Λ}$D- and B 0 →p$\bar{Λ}$D(*)- to be (25.1±2.6±3.5)×10 -6 and (33.6±6.3±4.4)×10 -6 , respectively, where the first uncertainties are statistical and the second are systematic. These results are not compatible with the predictions based on the generalized factorization approach. In addition, a threshold enhancement in the di-baryon (p$\bar{Λ}$) system is observed, consistent with that observed in similar B decays.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Correlation between stress-induced leakage current and dielectric degradation in ultra-porous SiOCH low-k materials

Stress-Induced Leakage Current (SILC) behavior during the dielectric degradation of ultra-porous SiOCH low-k materials was investigated. Under high voltage stress, SILC increases to a critical value before final hard breakdown. This SILC increase rate is mainly driven by the injected charges and is negligibly influenced by temperature and voltage. SILC is found to be transient and shows a t{sup −1} relaxation behavior, where t is the storage time at low voltages. This t{sup −1} transient behavior, described by the tunneling front model, is caused by both electron charging of neutral defects in the dielectric close to the cathode interface and discharging of donor defects close to the anode interface. These defects have a uniform density distribution within the probed depth range, which is confirmed by the observed flat band voltage shift results collected during the low voltage storage. By applying an additional discharging step after the low voltage storage, the trap energies and spatial distributions are derived. In a highly degraded low-k dielectric, the majority of defects have a trap depth between 3.4 eV and 3.6 eV and a density level of 1 × 10{sup 18 }eV{sup −1 }cm{sup −3}. The relation between the defect density N and the total amount of the injected charges Q is measured to be sub-linear, N ∼ Q{sup 0.45±0.07}. The physical nature of these stress-induced defects is suggested to be caused by the degradation of the Si-O based skeleton in the low-k dielectric.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Semi-inclusive studies of semileptonic B s decays at Belle

We present an analysis of the semi-inclusive decays B s → D s - X ℓ + ν and B s → D s * - X ℓ + ν , where X denotes a final state that may consist of additional hadrons or photons and ℓ is an electron or muon. The studied B s decays are contained in the 121.4 fb - 1 Υ ( 5 S ) data sample collected by the Belle detector at the KEKB asymmetric-energy e + e - collider. The branching fractions of the decays are measured to be B ( B s → D s - X ℓ + ν ) = [ 8.2 ± 0.2 ( stat ) ± 0.6 ( syst ) ± 1.4 ( ext ) ] % and B ( B s → D s * - X ℓ + ν ) = [ 5.4 ± 0.4 ( stat ) ± 0.4 ( syst ) ± 0.9 ( ext ) ] % , where the first two uncertainties are statistical and systematic and the last is due to external parameters. The measurement also provides an estimate of the B s ( * ) B ¯ s ( * ) production cross section, σ ( e + e - → B s ( * ) B ¯ s ( * ) ) = [ 53.8 ± 1.4 ( stat ) ± 4.0 ( syst ) ± 3.4 ( ext ) ] pb , at the center-of-mass energy s = 10.86 GeV .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗