Engineering Papers⌕ Search

Engineering topics

Li, Y.

Publications and source records attributed to Li, Y..

At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Measurement of the branching ratio of B ¯ 0 → D * + τ - ν ¯ τ relative to B ¯ 0 → D * + ℓ - ν ¯ ℓ decays with a semileptonic tagging method

Here, we report a measurement of the ratio R ( D * ) = B ( B ¯ 0 → D * + τ - ν ¯ τ ) / B ( B ¯ 0 → D * + ℓ - ν ¯ ℓ ) , where ℓ denotes an electron or a muon. The results are based on a data sample containing 772 × 1 0 6 B B ¯ pairs recorded at the Υ ( 4 S ) resonance with the Belle detector at the KEKB e + e - collider. We select a sample of B 0 B ¯ 0 pairs by reconstructing both B mesons in semileptonic decays to D * ∓ ℓ ± . We measure R ( D * ) = 0.302 ± 0.030 ( stat ) ± 0.011 ( syst ) , which is within 1.6 σ of the Standard Model theoretical expectation, where the standard deviation σ includes systematic uncertainties. We use this measurement to constrain several scenarios of new physics in a model-independent technique.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Study of excited Ξ c states decaying into Ξ c 0 and Ξ c + baryons

Here, with a data sample of 980 fb - 1 of e + e - annihilation data taken with the Belle detector operating at the KEKB asymmetric-energy e + e - collider, we discuss the results of a study of excited Ξ c states that decay, via the emission of photons and/or charged pions, into Ξ c 0 or Ξ c + ground state charmed-strange baryons. We present new measurements of the masses of all members of the Ξ c ' , Ξ c ( 2645 ) , Ξ c ( 2790 ) , Ξ c ( 2815 ) , and Ξ c ( 2980 ) isodoublets, measurements of the intrinsic widths of those that decay strongly, and evidence of previously unknown transitions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Measurement of the CKM angle φ 1 in B 0 → D ¯ ( * ) 0 h 0 , D ¯ 0 → K S 0 π + π - decays with time-dependent binned Dalitz plot analysis

Here, we show a measurement of the C P -violation parameter φ 1 obtained in a time-dependent analysis of B 0 → D ¯ ( * ) 0 h 0 decays followed by D ¯ 0 → K S 0 π + π - decay. A model-independent measurement is performed using the binned Dalitz plot technique. The measured value is φ 1 = 11.7 ° ± 7.8 ° ( stat ) ± 2.1 ° ( syst ) . Treating sin 2 φ 1 and cos 2 φ 1 as independent parameters, we obtain sin 2 φ 1 = 0.43 ± 0.27 ( stat ) ± 0.08 ( syst ) and cos 2 φ 1 = 1.06 ± 0.33 ( stat ) - 0.15 + 0.21 ( syst ) . The findings are obtained with a full data sample of 772 × 1 0 6 B B ¯ pairs collected near the Υ ( 4 S ) resonance with the Belle detector at the KEKB asymmetric-energy e + e - collider.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Path to AWAKE: Evolution of the concept

This paper describes the conceptual steps in reaching the design of the AWAKE experiment currently under construction at CERN. We start with an introduction to plasma wakefield acceleration and the motivation for using proton drivers. We then describe the self-modulation instability – a key to an early realization of the concept. This is then followed by the historical development of the experimental design, where the critical issues that arose and their solutions are described. We conclude with the design of the experiment as it is being realized at CERN and some words on the future outlook. A summary of the AWAKE design and construction status as presented in this conference is given in Gschwendtner et al. [1] .

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

Magnetostructural martensitic transformations with large volume changes and magneto-strains in all-d-metal Heusler alloys

The all-d-metal Mn{sub 2}-based Heusler ferromagnetic shape memory alloys Mn{sub 50}Ni{sub 40−x}Co{sub x}Ti{sub 10} (x = 8 and 9.5) are realized. With a generic comparison between d-metal Ti and main-group elements in lowering the transformation temperature, the magnetostructural martensitic transformations are established by further introducing Co to produce local ferromagnetic Mn-Co-Mn configurations. A 5-fold modulation and (3, −2) stacking of [00 10] of martensite are determined by X-ray diffraction and HRTEM analysis. Based on the transformation, a large magneto-strain of 6900 ppm and a large volume change of −2.54% are observed in polycrystalline samples, which makes the all-d-metal magnetic martensitic alloys of interest for magnetic/pressure multi-field driven applications.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Structural defects and recombination behavior of excited carriers in Cu(In,Ga)Se{sub 2} solar cells

The carriers’ behavior in neutral region (NTR) and space charged region (SCR) of Cu(In,Ga)Se{sub 2} thin film based solar cells has been investigated by temperature dependent photoluminescence (PL-T), electroluminescence (EL-T) and current-voltage (IV-T) from 10 to 300 K. PL-T spectra show that three kinds of defects, namely V{sub Se}, In{sub Cu} and (In{sub Cu}+V{sub Cu}), are localized within the band gap of NTR and SCR of CIGS layer, corresponding to the energy levels of E{sub C}-0.08, E{sub C}-0.20 and E{sub C}-0.25 eV, respectively. The In{sub Cu} and (In{sub Cu}+V{sub Cu}) deep level defects are non-radiative recombination centers at room temperature. The IV-T and EL-T analysis reveals that the injection modes of electrons from ZnO conduction band into Cu(In,Ga)Se{sub 2} layer are tunneling, thermally-excited tunneling and thermionic emission under 10-40, 60-160, and 180-300 K, respectively. At 10-160 K, the electrons tunnel into (In{sub Cu}+V{sub Cu}) and V{sub se} defect levels in band gap of SCR and the drifting is involved in the emission bands at 0.96 and 1.07 eV, which is the direct evidence for a tunneling assisted recombination. At 180-300 K, the electrons are directly injected into the Cu(In,Ga)Se{sub 2} conduction band, and the emission of 1.13 eV are ascribed to the transitions from the conduction band to the valence band.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Studies of charmed strange baryons in the Λ D final state at Belle

In this report, we discuss the discovery of Ξ c ( 3055 ) 0 , observed by its decay into the final-state Λ D 0 , and present the first observation and evidence of the decays of Ξ c ( 3055 ) + and Ξ c ( 3080 ) + into Λ D + . Furthermore, we perform a combined analysis of the Λ D + with the Σ c + + K - and Σ c * + + K - decay modes to measure the ratios of branching fractions, masses and widths with improved accuracy. We measure the ratios of branching fractions B ( Ξ c ( 3055 ) + → Λ D + ) / B ( Ξ c ( 3055 ) + → Σ c + + K - ) = 5.09 ± 1.01 ± 0.76 , B ( Ξ c ( 3080 ) + → Λ D + ) / B ( Ξ c ( 3080 ) + → Σ c + + K - ) = 1.29 ± 0.30 ± 0.15 , and B ( Ξ c ( 3080 ) + → Σ c * + + K - ) / B ( Ξ c ( 3080 ) + → Σ c + + K - ) = 1.07 ± 0.27 ± 0.04 , where the uncertainties are statistical and systematic. The analysis is performed using a 980 fb - 1 data sample collected with the Belle detector at the KEKB asymmetric-energy e + e - collider.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

RELATIVISTIC ELECTRONS PRODUCED BY RECONNECTING ELECTRIC FIELDS IN A LASER-DRIVEN BENCH-TOP SOLAR FLARE

Laboratory experiments have been carried out to model the magnetic reconnection process in a solar flare with powerful lasers. Relativistic electrons with energy up to megaelectronvolts are detected along the magnetic separatrices bounding the reconnection outflow, which exhibit a kappa-like distribution with an effective temperature of ∼10{sup 9} K. The acceleration of non-thermal electrons is found to be more efficient in the case with a guide magnetic field (a component of a magnetic field along the reconnection-induced electric field) than in the case without a guide field. Hardening of the spectrum at energies ≥500 keV is observed in both cases, which remarkably resembles the hardening of hard X-ray and γ -ray spectra observed in many solar flares. This supports a recent proposal that the hardening in the hard X-ray and γ -ray emissions of solar flares is due to a hardening of the source-electron spectrum. We also performed numerical simulations that help examine behaviors of electrons in the reconnection process with the electromagnetic field configurations occurring in the experiments. The trajectories of non-thermal electrons observed in the experiments were well duplicated in the simulations. Our numerical simulations generally reproduce the electron energy spectrum as well, except for the hardening of the electron spectrum. This suggests that other mechanisms such as shock or turbulence may play an important role in the production of the observed energetic electrons.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

CHESS upgrade with compact undulator magnets: Operating experience and first results

In November 2014 two in-air 1.5 m CHESS Compact Undulator (CCU) magnets built by KYMA S.R.l. were installed in Cornell Electron Storage Ring (CESR) in canted arrangement and after few days of commissioning their regular operation started. CCU magnets are compact, lightweight and cost efficient devices. They have very stable magnetic field integrals independent of deflection parameter value. This feature greatly simplifies the storage ring operation. The CCU concept was developed at Cornell in 2011 and the first 1 m in-vacuum CCU magnet was beam-tested in 2012. The article presents CCU concept and some details of the design. It describes also the layout of CCUs installation in CESR, their performance and characteristics. The current status of operation and future plans are discussed as well. Presently, at CHESS two CCU magnets provide radiation for 5 out of 11 experimental stations.

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

NSLS-II commissioning and operation

The National Synchrotron Light Source II at Brookhaven National Lab is a third-generation synchrotron radiation facility that has been commissioned in 2014. The facility is based on a 3 GeV electron storage ring, which will circulate 500 mA of beam current at 1 nm rad horizontal emittance. The storage ring is 792 meters in circumference and will accommodate more than 60 beamlines in the final built-out. The beamline sources range from insertion-devices located in straight sections, bending magnets or three-pole-wigglers configured in multiple branches. The NSLS-II storage ring commissioning was successfully completed in July 2014 and the facility delivered the first user light on October 23, 2014. Currently the storage ring reached 300 mA beam current and achieved 1 nm rad of horizontal emittance with 3 sets of Damping Wigglers. At this point six NSLS-II project beamlines are routinely taking photons with beam current at 150 mA. This paper reviews the NSLS-II accelerator design and commissioning experience.

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

Commissioning of the synchrotron radiation protection system and beamlines frontends at NSLS-II

The first eight insertion devices (IDs) at the NSLS-II were commissioned during the fall run of 2014. In this paper we discuss commissioning of the synchrotron radiation protection (SRP) system and beamline frontends (FE) for the respective IDs. We describe the diagnostics utilized if FE commissioning and a procedure that was used for the alignment of the photon beam from insertion devices in the beamline frontends. Then we discuss the current status of the SRP system and operation of the commissioned frontends.

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

Search for a massive invisible particle X 0 in B + → e + X 0 and B + → μ + X 0 decays

We present a search for a non-Standard-Model invisible particle X 0 in the mass range 0.1-1.8GeV/c 2 in B + →e + X 0 and B + →μ+X 0 decays. The results are obtained from a 711 fb -1 data sample that corresponds to 772×10 6 BB pairs, collected at the Υ(4S) resonance with the Belle detector at the KEKB e + e - collider. One B meson is fully reconstructed in a hadronic mode to determine the momentum of the lepton of the signal decay in the rest frame of the recoiling partner B meson. We find no evidence of a signal and set upper limits on the order of 10 -6 .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Observation of fast expansion velocity with insulating tungsten wires on ∼80 kA facility

This paper presents experimental results on the effects of insulating coatings on tungsten planar wire array Z-pinches on an 80 kA, 100 ns current facility. Expansion velocity is obviously increased from ∼0.25 km/s to ∼3.5 km/s by using the insulating coatings. It can be inferred that the wire cores are in gaseous state with this fast expansion velocity. An optical framing camera and laser probing images show that the standard wire arrays have typical ablation process which is similar to their behaviors on mega-ampere facilities. The ablation process and precursor plasma are suppressed for dielectric tungsten wires. The wire array implosion might be improved if these phenomena can be reproduced on Mega-ampere facilities.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

SHOCK CONNECTIVITY IN THE 2010 AUGUST AND 2012 JULY SOLAR ENERGETIC PARTICLE EVENTS INFERRED FROM OBSERVATIONS AND ENLIL MODELING

During periods of increased solar activity, coronal mass ejections (CMEs) can occur in close succession and proximity to one another. This can lead to the interaction and merger of CME ejecta as they propagate in the heliosphere. The particles accelerated in these shocks can result in complex solar energetic particle (SEP) events, as observing spacecraft form both remote and local shock connections. It can be challenging to understand these complex SEP events from in situ profiles alone. Multipoint observations of CMEs in the near-Sun environment, from the Solar Terrestrial Relations Observatory –Sun Earth Connection Coronal and Heliospheric Investigation and the Solar and Heliospheric Observatory Large Angle and Spectrometric Coronagraph, greatly improve our chances of identifying the origin of these accelerated particles. However, contextual information on conditions in the heliosphere, including the background solar wind conditions and shock structures, is essential for understanding SEP properties well enough to forecast their characteristics. Wang–Sheeley–Arge WSA-ENLIL + Cone modeling provides a tool to interpret major SEP event periods in the context of a realistic heliospheric model and to determine how much of what is observed in large SEP events depends on nonlocal magnetic connections to shock sources. We discuss observations of the SEP-rich periods of 2010 August and 2012 July in conjunction with ENLIL modeling. We find that much SEP activity can only be understood in the light of such models, and in particular from knowing about both remote and local shock source connections. These results must be folded into the investigations of the physics underlying the longitudinal extent of SEP events, and the source connection versus diffusion pictures of interpretations of SEP events.

79 ASTRONOMY AND ASTROPHYSICS↗