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Sun, L.

Publications and source records attributed to Sun, L..

At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

24 GHz microwave mode converter optimized for superconducting ECR ion source SECRAL

Over-sized round waveguide with a diameter about Ø33.0 mm excited in the TE{sub 01} mode has been widely adopted for microwave transmission and coupling to the ECR (Electron Cyclotron Resonance) plasma with the superconducting ECR ion sources operating at 24 or 28 GHz, such as SECRAL and VENUS. In order to study the impact of different microwave modes on ECRH (Electron Cyclotron Resonance Heating) efficiency and especially the production of highly charged ions, a set of compact and efficient TE{sub 01}-HE{sub 11} mode conversion and coupling system applicable to 24 GHz SECRAL whose overall length is 330 mm has been designed, fabricated and tested. Good agreements between off-line tests and calculation results have been achieved, which indicates the TE{sub 01}-HE{sub 11} converter meets the application design. The detailed results of the optimized coupling system will be presented in the paper.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Observation of B ¯ → D ( * ) π + π - ℓ - ν ¯ Decays in e + e - Collisions at the Υ ( 4 S ) Resonance

We report on measurements of the decays of $\bar{B}$ mesons into the semileptonic final states $\bar{B}$→D(*)π + π - l - $\bar{v}$, where D(*) represents a D or D* meson and l - is an electron or a muon. These measurements are based on 471×10 6 B$\bar{B}$ pairs recorded with the BABAR detector at the SLAC asymmetric B factory PEP-II. We determine the branching fraction ratios R$(*)\atop{π+π-}$ = B($\bar{B}$→D(*)π + π - l - $\bar{v}$)/B($\bar{B}$→D(*)l - $\bar{v}$) using events in which the second B meson is fully reconstructed. We find R π+π- =0.067 ± 0.010 ± 0.008 and R$*\atop{π+π-}$ = 0.019 ± 0.005 ± 0.004, where the first uncertainty is statistical and the second is systematic. Lastly, based on these results and assuming isospin invariance, we estimate that $\bar{B}$→D(*)ππl - $\bar{v}$ decays, where π denotes either a π ± and π 0 meson, account for up to half the difference between the measured inclusive semileptonic branching fraction to charm hadrons and the corresponding sum of previously measured exclusive branching fractions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Measurement of the I = 1 / 2 K π S -wave amplitude from Dalitz plot analyses of η c → K K ¯ π in two-photon interactions

Here we study the processes γγ→K$0\atop{S}$K ± π ∓ and γγ→K + K - π 0 using a data sample of 519 fb -1 recorded with the BABAR detector operating at the SLAC PEP-II asymmetric-energy e + e - collider at center-of-mass energies at and near the Υ(nS) (n=2, 3, 4) resonances. We observe ηc decays to both final states and perform Dalitz plot analyses using a model-independent partial wave analysis technique. This allows a model-independent measurement of the mass-dependence of the I=1/2 Kπ S-wave amplitude and phase. A comparison between the present measurement and those from previous experiments indicates similar behavior for the phase up to a mass of 1.5 GeV/c 2 . In contrast, the amplitudes show very marked differences. Lastly, the data require the presence of a new a 0 (1950) resonance with parameters m=1931±14±22 MeV/c 2 and Γ=271±22±29 MeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Elemental intermixing within an ultrathin SrRuO{sub 3} electrode layer in epitaxial heterostructure BaTiO{sub 3}/SrRuO{sub 3}/SrTiO{sub 3}

Aberration corrected scanning transmission electron microscopy is used to directly observe atom columns in an epitaxial BaTiO{sub 3} thin film deposited on a 3.6 nm-thick SrRuO{sub 3} electrode layer above an SrTiO{sub 3} (001) substrate. Compositional gradients across the heterointerfaces were examined using electron energy-loss spectroscopy techniques. It was found that a small amount of Ba and Ti had diffused into the SrRuO{sub 3} layer, and that this layer contained a non-negligible concentration of oxygen vacancies. Such point defects are expected to degrade the electrode’s electronic conductivity drastically, resulting in a much longer screening length. This may explain the discrepancy between experimental measurements and theoretical estimates of the ferroelectric critical thickness of a BaTiO{sub 3} ferroelectric barrier sandwiched between metallic SrRuO{sub 3} electrodes, since theoretical calculations generally assume ideal (stoichiometric) perovskite SrRuO{sub 3}.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Collins asymmetries in inclusive charged K K and K π pairs produced in e + e - annihilation

Here, we present measurements of Collins asymmetries in the inclusive process e + e - →h 1 h 2 X, h 1 h 2 = KK, Kπ, ππ, at the center-of-mass energy of 10.6 GeV, using a data sample of 468 fb -1 collected by the BABAR experiment at the PEP-II B factory at SLAC National Accelerator Center. Considering hadrons in opposite thrust hemispheres of hadronic events, we observe clear azimuthal asymmetries in the ratio of unlike sign to like sign, and unlike sign to all charged h 1 h 2 pairs, which increase with hadron energies. The Kπ asymmetries are similar to those measured for the ππ pairs, whereas those measured for high-energy KK pairs are, in general, larger.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Current Status of Helium-3 Alternative Technologies for Nuclear Safeguards

International safeguards inspectorates (e.g., International Atomic Energy Agency {IAEA}, or Euratom) rely heavily on neutron assay techniques, and in particular, on coincidence counters for the verification of declared nuclear materials under safeguards and for monitoring purposes. While 3 He was readily available, the reliability, safety, ease of use, gamma-ray insensitivity, and high intrinsic thermal neutron detection efficiency of 3 He-based detectors obviated the need for alternative detector technologies. However, the recent decline of the 3 He gas supply has triggered international efforts to develop and field neutron detectors that make use of alternative materials. In response to this global effort, the U.S. Department of Energy’s (DOE) National Nuclear Security Administration (NNSA) and Euratom launched a joint effort aimed at bringing together international experts, technology users and developers in the field of nuclear safeguards to discuss and evaluate the proposed 3 He alternative materials and technologies. The effort involved a series of two workshops focused on detailed overviews and viability assessments of various 3 He alternative technologies for use in nuclear safeguards applications. The key objective was to provide a platform for collaborative discussions and technical presentations organized in a compact, workshop-like format to stimulate interactions among the participants. The meetings culminated in a benchmark exercise providing a unique opportunity for the first inter-comparison of several available alternative technologies. This report provides an overview of the alternative technology efforts presented during the two workshops along with a summary of the benchmarking activities and results. The workshop recommendations and key consensus observations are discussed in the report, and used to outline a proposed path forward and future needs foreseeable in the area of 3 He-alternative technologies.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Measurement of initial-state–final-state radiation interference in the processes e + e – → μ + μ – γ and e + e – → π + π – γ [Measurement of ISR-FSR interference in the processes e + e – → μ + μ – γ and e + e – → π + π – γ ]

Charge asymmetry in the processes e + e – → μ + μ – γ and e + e – → π + π – γ is measured using 232 fb –1 of data collected with the BABAR detector at e + e – center-of-mass energies near 10.58 GeV. An observable is introduced and shown to be very robust against detector asymmetries while keeping a large sensitivity to the physical charge asymmetry that results from the interference between initial- and final-state radiation (FSR). The asymmetry is determined as a function of the invariant mass of the final-state tracks from production threshold to a few GeV/c 2 . It is compared to the expectation from QED for e + e – → μ + μ – γ, and from theoretical models for e + e – → π + π – γ. A clear interference pattern is observed in e + e – → π + π – γ, particularly in the vicinity of the f 2 (1270) resonance. As a result, the inferred rate of lowest-order FSR production is consistent with the QED expectation for e + e – → μ + μ – γ, and is negligibly small for e + e – → π + π – γ.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Study of the e + e - → K + K - reaction in the energy range from 2.6 to 8.0 GeV

The e + e - →K + K - cross section and charged-kaon electromagnetic form factor are measured in the e + e - center-of-mass energy range (E) from 2.6 to 8.0 GeV using the initial-state radiation technique with an undetected photon. The study is performed using 469 fb-1 of data collected with the BABAR detector at the PEP-II2 e + e - collider at center-of-mass energies near 10.6 GeV. The form factor is found to decrease with energy faster than 1/E 2 and approaches the asymptotic QCD prediction. Production of the K + K - final state through the J/ψ and ψ(2S) intermediate states is observed. The results for the kaon form factor are used together with data from other experiments to perform a model-independent determination of the relative phases between electromagnetic (single-photon) and strong amplitudes in J/ψ and ψ(2S)→K + K - decays. The values of the branching fractions measured in the reaction e + e - →K + K - are shifted relative to their true values due to interference between resonant and nonresonant amplitudes. The values of these shifts are determined to be about ±5% for the J/ψ meson and ±15% for the ψ(2S) meson.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Spectroscopic study of Gd nanostructures quantum confined in Fe corrals

Low dimensional nanostructures have attracted attention due to their rich physical properties and potential applications. The essential factor for their functionality is their electronic properties, which can be modified by quantum confinement. Here the electronic states of Gd atom trapped in open Fe corrals on Ag(111) were studied via scanning tunneling spectroscopy. A single spectroscopic peak above the Fermi level is observed after Gd adatoms are trapped inside Fe corrals, while two peaks appear in empty corrals. The single peak position is close to the higher energy peak of the empty corrals. These findings, attributed to quantum confinement of the corrals and Gd structures trapped inside, are supported by tight-binding calculations. As a result, this demonstrates and provides insights into atom trapping in open corrals of various diameters, giving an alternative approach to modify the properties of nano-objects.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Watching the dynamics of electrons and atoms at work in solar energy conversion

The photochemical reactions performed by transition metal complexes have been proposed as viable routes towards solar energy conversion and storage into other forms that can be conveniently used in our everyday applications. In order to develop efficient materials, it is necessary to identify, characterize and optimize the elementary steps of the entire process on the atomic scale. To this end, we have studied the photoinduced electronic and structural dynamics in two heterobimetallic ruthenium–cobalt dyads, which belong to the large family of donor–bridge–acceptor systems. Using a combination of ultrafast optical and X-ray absorption spectroscopies, we can clock the light-driven electron transfer processes with element and spin sensitivity. In addition, the changes in local structure around the two metal centers are monitored. These experiments show that the nature of the connecting bridge is decisive for controlling the forward and the backward electron transfer rates, a result supported by quantum chemistry calculations. More generally, this work illustrates how ultrafast optical and X-ray techniques can disentangle the influence of spin, electronic and nuclear factors on the intramolecular electron transfer process. Finally, some implications for further improving the design of bridged sensitizer-catalysts utilizing the presented methodology are outlined.

14 SOLAR ENERGY↗
DOE OSTI2015

Search for Long-Lived Particles in e + e - Collisions

We present a search for a neutral, long-lived particle L that is produced in e + e - collisions and decays at a significant distance from the e + e - interaction point into various flavor combinations of two oppositely charged tracks. The analysis uses an e + e - data sample with a luminosity of 489.1 fb -1 collected by the BABAR detector at the γ (4S), γ (3S), and γ (2S) resonances and just below the γ (4S). Fitting the two-track mass distribution in search of a signal peak, we do not observe a significant signal, and set 90% confidence level upper limits on the product of the L production cross section, branching fraction, and reconstruction efficiency for six possible two-body L decay modes as a function of the L mass. The efficiency is given for each final state as a function of the mass, lifetime, and transverse momentum of the candidate, allowing application of the upper limits to any production model. In addition, upper limits are provided on the branching fraction B(B→X s L), where X s is a strange hadronic system.

Lees, J. P.↗