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Li, Y.

Publications and source records attributed to Li, Y..

At least 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

First observation of γ γ → p p ¯ K + K - and search for exotic baryons in p K systems

The process γ γ → p p ¯ K + K - and its intermediate processes are measured for the first time using a 980 fb - 1 data sample collected with the Belle detector at the KEKB asymmetric-energy e + e - collider. The production of p p ¯ K + K - and a Λ ( 1520 ) 0 ( Λ ¯ ( 1520 ) 0 ) signal in the p K - ( p ¯ K + ) invariant mass spectrum are clearly observed. However, no evidence for an exotic baryon near 1540 MeV / c 2 , denoted as Θ ( 1540 ) 0 ( Θ ¯ ( 1540 ) 0 ) or Θ ( 1540 ) + + ( Θ ( 1540 ) - -- ), is seen in the p K - ( p ¯ K + ) or p K + ( p ¯ K - ) invariant mass spectra. Cross sections for γ γ → p p ¯ K + K - , Λ ( 1520 ) 0 p ¯ K + + c . c . and the products σ ( γ γ → Θ ( 1540 ) 0 p ¯ K + + c . c . ) B ( Θ ( 1540 ) 0 → p K - ) and σ ( γ γ → Θ ( 1540 ) + + p ¯ K - + c . c . ) B ( Θ ( 1540 ) + + → p K + ) are measured. We also determine upper limits on the products of the χ c 0 and χ c 2 two-photon decay widths and their branching fractions to p p ¯ K + K - at the 90% credibility level.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

First Observation of the Doubly Cabibbo-Suppressed Decay of a Charmed Baryon: Λ c + → p K + π -

We report the first observation of the decay Λ c + → p K + π - using a 980 fb - 1 data sample collected by the Belle detector at the KEKB asymmetric-energy e + e - collider. This is the first observation of a doubly Cabibbo-suppressed decay of a charmed baryon. We measure the branching ratio of this decay with respect to its Cabibbo-favored counterpart to be B ( Λ c + → p K + π - ) / B ( Λ c + → p K - π + ) = ( 2.35 ± 0.27 ± 0.21 ) × 10 - 3 , where the uncertainties are statistical and systematic, respectively.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Search for X Y Z states in Υ ( 1 S ) inclusive decays

The branching fractions of the Υ ( 1 S ) inclusive decays into final states with a J / ψ or a ψ ( 2 S ) are measured with higher precision to be B ( Υ ( 1 S ) → J / ψ + anything ) = ( 5.25 ± 0.13 ( stat ) ± 0.25 ( syst ) ) × 10 - 4 and B ( Υ ( 1 S ) → ψ ( 2 S ) + anything ) = ( 1.23 ± 0.17 ( stat ) ± 0.11 ( syst ) ) × 10 - 4 . The first search for Υ ( 1 S ) decays into X Y Z states that decay into a J / ψ or a ψ ( 2 S ) plus one or two charged tracks yields no significant signals for X Y Z states in any of the examined decay modes, and upper limits on their production rates in Υ ( 1 S ) inclusive decays are determined.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Search for the decay B 0 → Φ γ

We have searched for the decay B 0 → Φγ using the full Belle data set of 772 × 10 6 BB¯ pairs collected at the Υ(4S) resonance with the Belle detector at the KEKB e+e– collider. No signal is observed, and we set an upper limit on the branching fraction of B(B 0 → Φγ) < 1.0 × 10 –7 at the 90% confidence level. Here, this is the most stringent limit on this decay mode to date.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

A Backward Euler Doubling Feasibility Study Based on Thorium Series Cascade

The solution to the Bateman equations of radioactive decay are central to burnup calculations for operational nuclear reactors. There are several excellent methods of solving the equations of radioactive decay, with the CRAM algorithm as one of the best, at least for constant flux burnup. In this work, we attempt to investigate the feasibility of a relatively straight forward algorithm based simply on finite difference and doubling and apply the resulting benchmark to a recently developed decay chain formulation. A simple Backward Euler Doubling Finite Difference (BEDFD) method for solving first order ordinary differential equations is developed with enhanced precision through the convergence acceleration. Numerical results of two analytically solvable test problems clearly demonstrated that this newly proposed method is robust and accurate. Therefore, this method could be promising in solving larger depletion problems-our next effort in our comparisons with TTA. (authors)

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

A 20-liter test stand with gas purification for liquid argon research

Here, we describe the design of a 20-liter test stand constructed to study fundamental properties of liquid argon (LAr). Moreover, this system utilizes a simple, cost-effective gas argon (GAr) purification to achieve high purity, which is necessary to study electron transport properties in LAr. An electron drift stack with up to 25 cm length is constructed to study electron drift, diffusion, and attachment at various electric fields. Finally, a gold photocathode and a pulsed laser are used as a bright electron source. The operational performance of this system is reported.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Simultaneous, single-pulse, synchrotron x-ray imaging and diffraction under gas gun loading

We develop a mini gas gun system for simultaneous, single-pulse, x-ray diffraction and imaging under high strain-rate loading at the beamline 32-ID of the Advanced Photon Source. In order to increase the reciprocal space covered by a small-area detector, a conventional target chamber is split into two chambers: a narrowed measurement chamber and a relief chamber. The gas gun impact is synchronized with synchrotron x-ray pulses and high-speed cameras. Depending on a camera’s capability, multiframe imaging and diffraction can be achieved. The proof-of-principle experiments are performed on single-crystal sapphire. The diffraction spots and images during impact are analyzed to quantify lattice deformation and fracture; diffraction peak broadening is largely caused by fracture-induced strain inhomogeneity. Finally, our results demonstrate the potential of such multiscale measurements for revealing and understanding high strain-rate phenomena at dynamic extremes.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Rapid Crossing of a Resonance During Tune Modulation by Synchrotron Oscillations

It had become a standard practice to constrain the particle’s tune footprint while designing the ring lattice so that the particle tunes fit between harmful resonances that limit ring dynamic aperture (DA). This approach, known as “tune confinement”, puts tight limits on the magnitude of the tune shifts with amplitude and with momentum. The latter requires labor-intensive optimization of the off-energy dynamic aperture and control over the corresponding tune footprint for the large energy deviations and is a prerequisite to achieving reasonable lifetime if it is dominated by the Touschek scattering. As nonlinearities of the modern ring lattices are much enhanced as compared with the previous generation of synchrotron light sources, it is becoming more and more difficult to keep the off-momentum tune footprint confined. While one could reach reasonable on-energy DA suitable for injection into the machine, the off-energy DA optimization is much more complex and needs to satisfy more constraints so to reach large energy acceptance and secure decent lifetime at the high ring current. In certain cases when the lattice solution with the confined off-energy tune footprint cannot be found, one may ask whether crossing of a resonance stopband from off-momentum particle will lead to loss of this particle. Intuitively, if the particle crosses the stopband quickly, one may expect that the betatron oscillation amplitude will not increase substantially thereby keeping the particle within the machine acceptance. At the same time the tight tolerances of the modern lattice elements as designed and produced afford much narrower resonance stopbands being compared with the machines built decades ago. Under these circumstances the question above may be asked as what are the conditions for operating a ring with a large chromatic tune footprint, which crosses resonances, while not observing particle losses. In this paper we try to answer the questions above by studying the model of a particle with large initial momentum deviation (as, for example, driven by the Touschek scattering event), which crosses stopband of a half-integer resonance while executing synchrotron oscillations in the highly chromatic ring lattice.

36 MATERIALS SCIENCE↗
DOE OSTI2016

OBSERVATIONS OF AN X-SHAPED RIBBON FLARE IN THE SUN AND ITS THREE-DIMENSIONAL MAGNETIC RECONNECTION

We report evolution of an atypical X-shaped flare ribbon that provides novel observational evidence of three-dimensional (3D) magnetic reconnection at a separator. The flare occurred on 2014 November 9. High-resolution slit-jaw 1330 Å images from the Interface Region Imaging Spectrograph reveal four chromospheric flare ribbons that converge and form an X-shape. Flare brightening in the upper chromosphere spreads along the ribbons toward the center of the “X” (the X-point), and then spreads outward in a direction more perpendicular to the ribbons. These four ribbons are located in a quadrupolar magnetic field. Reconstruction of magnetic topology in the active region suggests the presence of a separator connecting to the X-point outlined by the ribbons. The inward motion of flare ribbons in the early stage therefore indicates 3D magnetic reconnection between two sets of non-coplanar loops that approach laterally, and reconnection proceeds downward along a section of vertical current sheet. Coronal loops are also observed by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory confirming the reconnection morphology illustrated by ribbon evolution.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Simultaneous and coordinated rotational switching of all molecular rotors in a network

A range of artificial molecular systems have been created that can exhibit controlled linear and rotational motion. In the development of such systems, a key step is the addition of communication between molecules in a network. Here, we show that a two-dimensional array of dipolar molecular rotors can undergo simultaneous rotational switching by applying an electric field from the tip of a scanning tunnelling microscope. Several hundred rotors made from porphyrin-based double-decker complexes can be simultaneously rotated when in a hexagonal rotor network on a Cu(111) surface by applying biases above ±1 V at 80 K. The phenomenon is observed only in a hexagonal rotor network due to the degeneracy of the ground state dipole rotational energy barrier of the system. Defects are essential to increase electric torque on the rotor network and to stabilize the switched rotor domains. At low biases and low initial rotator angles, slight reorientations of individual rotors can occur resulting in the rotator arms pointing in different directions. In conclusion, analysis reveals that the rotator arm directions here are not random, but are coordinated to minimize energy via cross talk among the rotors through dipolar interactions.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

The conversion of CESR to operate as the Test Accelerator, CesrTA. Part 3: Electron cloud diagnostics

Cornell's electron/positron storage ring (CESR) was modified over a series of accelerator shutdowns beginning in May 2008, which substantially improves its capability for research and development for particle accelerators. CESR's energy span from 1.8 to 5.6 GeV with both electrons and positrons makes it ideal for the study of a wide spectrum of accelerator physics issues and instrumentation related to present light sources and future lepton damping rings. Additionally a number of these are also relevant for the beam physics of proton accelerators. This paper is the third in a series of four describing the conversion of CESR to the test accelerator, CESRTA. The first two papers discuss the overall plan for the conversion of the storage ring to an instrument capable of studying advanced accelerator physics issues [1] and the details of the vacuum system upgrades [2]. This paper focuses on the necessary development of new instrumentation, situated in four dedicated experimental regions, capable of studying such phenomena as electron clouds (ECs) and methods to mitigate EC effects. The fourth paper in this series describes the vacuum system modifications of the superconducting wigglers to accommodate the diagnostic instrumentation for the study of EC behavior within wigglers. Lastly, while the initial studies of CESRTA focused on questions related to the International Linear Collider damping ring design, CESRTA is a very versatile storage ring, capable of studying a wide range of accelerator physics and instrumentation questions.

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

First model-independent Dalitz analysis of B 0 → DK* 0 , D→K$^{0}_{S}$π + π – decay

We report a measurement of the amplitude ratio r S of B 0 → D 0 K* 0 and B 0 → D 0 ¯K* 0 decays with a Dalitz analysis of D → K$^{0}_{S}$π + π – decays, for the first time using a model-independent method. We set an upper limit rS<0.87 at the 68\% confidence level, using the full data sample of 772×10 6 BB¯ pairs collected at the Υ(4S) resonance with the Belle detector at the KEKB e + e – collider. This result is obtained from observables x–= +0.4$^{+1.0+0.0}_{–0.6–0.1}$ ± 0.0, y– = –0.6$^{+0.8+0.1}_{–1.0–0.0}$ ± 0.1, x + = +0.1$^{+0.7+0.0}_{–0.4–0.1}$ ± 0.1 and y + = +0.3$^{+0.5+0.0}_{–0.8–0.1}$ ± 0.1, where x ± = r S cos(δ S ± Φ 3 ), y ± = r S sin(δ S ± Φ 3 ) and Φ 3 (δ S ) is the weak (strong) phase difference between B 0 → D 0 K* 0 and B 0 → D¯ 0 K* 0 .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Multi-period G-mode pulsations of a pre-He-WD star in the eclipsing binary KIC 9164561

We report the discovery of a new pulsating pre-He-WD in the EL CVn-type binary KIC 9164561. Light curve modeling and frequency analysis of the binary system were carried out based on short-cadence Kepler photometry. Combined with the radial-velocity solution, revised physical parameters of the binary system were determined. The component KIC 9164561B was confirmed to be a pre-He-WD star with M = 0.213±0.012M{sub ⊙}, R = 0.283±0.006R{sub ⊙}, and T{sub eff} = 10650±200 K. In addition to the light changes due to an eclipse, pulsational light variations of the pre-He-WD star were detected. The Fourier analysis reveals at least 52 frequencies, with the dominant one at 313.4 μHz. A brief mode identification indicates that the pre-He-WD star pulsates in g-modes with an average period spacing of ΔΠ{sub l=1} = 80.87 s. Moreover, a number of multiplets due to rotational splitting were identified from the frequency spectra. The rotational period of the pulsating pre-He-WD star was found to equal to the orbital period, indicating that KIC 9164561B is in synchronous rotation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Inclusive and exclusive measurements of B decays to χ c 1 and χ c 2 at Belle

We report inclusive and exclusive measurements for χ c1 and χ c2 production in B decays. We measure B(B→ χc1 X) = (3.03 ± 0.05(stat) ± 0.24(syst)) × 10 –3 and B(B→χ c2 X) = (0.70 ± 0.06(stat) ± 0.10(syst)) × 10 –3 . For the first time, χ c2 production in exclusive B decays in the modes B 0 →χ c2 π – K + and B + →χ c2 π + π – K + has been observed, along with first evidence for the B + →χ c2 π + K$^{0}_{S}$ decay mode. For χ c1 production, we report the first observation in the B + →χ c1 π + π – K + , B 0 →χ c1 π + π – K$^{0}_{S}$ and B 0 →χ c1 π 0 π – K + decay modes. Using these decay modes, we observe a difference in the production mechanism of χ c2 in comparison to χ c1 in B decays. In addition, we report searches for X(3872) and χ c1 (2P) in the B + →(χ c1 π + π – )K + decay mode. In conclusion, the reported results use 772 × 10 6 BB¯ events collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e + e – collider.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Emittance and lifetime measurement with damping wigglers

National Synchrotron Light Source II (NSLS-II) is a new third-generation storage ring light source at Brookhaven National Laboratory. The storage ring design calls for small horizontal emittance (<1 nm-rad) and diffraction-limited vertical emittance at 12 keV (8 pm-rad). Achieving low value of the beam size will enable novel user experiments with nm-range spatial and meV-energy resolution. The high-brightness NSLS-II lattice has been realized by implementing 30-cell double bend achromatic cells producing the horizontal emittance of 2 nm rad and then halving it further by using several Damping Wigglers (DWs). This paper is focused on characterization of the DW effects in the storage ring performance, namely, on reduction of the beam emittance, and corresponding changes in the energy spread and beam lifetime. The relevant beam parameters have been measured by the X-ray pinhole camera, beam position monitors, beam filling pattern monitor, and current transformers. In this paper, we compare the measured results of the beam performance with analytic estimates for the complement of the 3 DWs installed at the NSLS-II.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Study of B 0 → ρ + ρ – decays and implications for the CKM angle Φ 2

We present a measurement of the branching fraction and the longitudinal polarization fraction of B 0 → ρ + ρ – decays, as well as the time-dependent CP violating parameters in decays into longitudinally polarized ρ + ρ – pairs with Belle’s final data set of 772 × 10 6 BB¯ pairs, at the Υ(4S) resonance, collected at the asymmetric-energy e + e – collider KEKB. We obtain B(B 0 → ρ + ρ – ) = (28.3 ± 1.5(stat) ± 1.5(syst)) × 10 –6 , f L = 0.988 ± 0.012(stat) ± 0.023(syst), A CP = 0.00 ± 0.10(stat) ± 0.06(syst), S CP = –0.13 ± 0.15(stat) ± 0.05(syst). As a result, we perform an isospin analysis to constrain the Cabibbo-Kobayashi-Maskawa angle Φ 2 and obtain two solutions with Φ 2 = (93.7 ± 10.6)°, being most compatible with other Standard-Model based fits to the data.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗