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Deng, J.

Publications and source records attributed to Deng, J..

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Isolation of flow and nonflow correlations by two- and four-particle cumulant measurements of azimuthal harmonics in s NN = 200 GeV Au+Au collisions

A data-driven method was applied to Au+Au collisions at root S-NN = 200 GeV made with the STAR detector at RHIC to isolate pseudorapidity distance Delta eta-dependent and Delta eta-independent correlations by using two- and four-particle azimuthal cumulant measurements. We identified a Delta eta-independent component of the correlation, which is dominated by anisotropic flow and flow fluctuations. It was also found to be independent of. within the measured range of pseudorapidity vertical bar eta vertical bar < 1. In 20-30% central Au+Au collisions, the relative flow fluctuation was found to be 34% +/- 2%(stat.) +/- 3%(sys.) for particles with transverse momentum p(T) less than 2 GeV/c. The Delta eta-dependent part, attributed to nonflow correlations, is found to be 5% +/- 2%(sys.) relative to the flow of the measured second harmonic cumulant at vertical bar Delta eta vertical bar > 0.7. (C) 2015 The Authors. Published by Elsevier B.V.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2015

Charged-to-neutral correlation at forward rapidity in Au+Au collisions at s NN = 200 GeV

Event-by-event fluctuations of the ratio of inclusive charged to photon multiplicities at forward rapidity in Au+Au collision at √s NN =200 GeV have been studied. Dominant contribution to such fluctuations is expected to come from correlated production of charged and neutral pions. We search for evidences of dynamical fluctuations of different physical origins. Observables constructed out of moments of multiplicities are used as measures of fluctuations. Mixed events and model calculations are used as baselines. Results are compared to the dynamical net-charge fluctuations measured in the same acceptance. A non-zero statistically significant signal of dynamical fluctuations is observed in excess to the model prediction when charged particles and photons are measured in the same acceptance. Thus, we find that, unlike dynamical net-charge fluctuation, charge-neutral fluctuation is not dominated by correlation due to particle decay. Results are compared to the expectations based on the generic production mechanism of pions due to isospin symmetry, for which no significant (< 1%) deviation is observed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

Note: A pulsed laser ion source for linear induction accelerators

We have developed a high-current laser ion source for induction accelerators. A copper target was irradiated by a frequency-quadrupled Nd:YAG laser (266 nm) with relatively low intensities of 10{sup 8} W/cm{sup 2}. The laser-produced plasma supplied a large number of Cu{sup +} ions (∼10{sup 12} ions/pulse) during several microseconds. Emission spectra of the plasma were observed and the calculated electron temperature was about 1 eV. An induction voltage adder extracted high-current ion beams over 0.5 A/cm{sup 2} from a plasma-prefilled gap. The normalized beam emittance measured by a pepper-pot method was smaller than 1 π mm mrad.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Λ Λ Correlation Function in Au + Au Collisions at s N N = 200 GeV

We present Lambda Lambda correlation measurements in heavy-ion collisions for Au + Au collisions at root s(NN) = 200 GeV using the STAR experiment at the Relativistic Heavy-Ion Collider. The Lednicky-Lyuboshitz analytical model has been used to fit the data to obtain a source size, a scattering length and an effective range. Implications of the measurement of the Lambda Lambda correlation function and interaction parameters for dihyperon searches are discussed.

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

Dielectron Azimuthal Anisotropy at mid-rapidity in Au+Au collisions at root s=200GeV

We report on the first measurement of the azimuthal anisotropy (v₂) of dielectrons (e⁺e⁻ pairs) at mid-rapidity from √( s NN)=200 GeV Au + Au collisions with the STAR detector at the Relativistic Heavy Ion Collider (RHIC), presented as a function of transverse momentum (p T ) for different invariant-mass regions. In the mass region Mee<1.1 GeV/c² the dielectron v₂ measurements are found to be consistent with expectations from π⁰,η,ω, and Φ decay contributions. In the mass region 1.1 ee <2.9GeV/c², the measured dielectron v₂ is consistent, within experimental uncertainties, with that from the cc¯ contributions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

Observation of D 0 meson nuclear modifications in Au + Au collisions at s NN = 200 GeV

We report the first measurement of charmed-hadron (D 0 ) production via the hadronic decay channel (D 0 → K - + π + ) in Au + Au collisions at √ s NN = 200 GeV with the STAR experiment. The charm production cross section per nucleon-nucleon collision at midrapidity scales with the number of binary collisions, N bin , from p + p to central Au + Au collisions. The D 0 meson yields in central Au + Au collisions are strongly suppressed compared to those in p + p scaled by N bin , for transverse momenta p T > 3 GeV/c, demonstrating significant energy loss of charm quarks in the hot and dense medium. Here, an enhancement at intermediate p T is also observed. Model calculations including strong charm-medium interactions and coalescence hadronization describe our measurements.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Effects of confinements on morphology of In{sub x}Ga{sub 1–x}As thin film grown on sub-micron patterned GaAs substrate: Elastoplastic phase field model

An elastoplastic phase field model is developed to investigate the role of lateral confinement on morphology of thin films grown heteroepitaxially on patterned substrates. Parameters of the model are chosen to represent In{sub x}Ga{sub 1-x}As thin films growing on GaAs patterned with SiO₂. We determined the effect of misfit strain on morphology of thin films grown in 0.5 μm patterns with non-uniform deposition flux. Growth of islands inside patterns can be controlled by non-uniformity of deposition flux, misfit strain between film and the substrate, and also strain energy relaxation due to plastic deformation. Our results show that the evolution of island morphology depends non-monotonically on indium content and associated misfit strain due to coupling between the plastic relaxation and the confinements effects. Low indium concentration (0%–40%) causes formation of instabilities with relatively long wavelengths across the width of the pattern. Low surface diffusion (due to low indium concentration) and fewer islands across the pattern (due to small misfit strain) lead to formation and growth of islands near the walls driven by overflow flux. Further increase in indium concentration (40%–75%) increases the lattice mismatch and surface diffusivity of the film, and also activates plastic deformation mechanism, which leads to coalescence of islands usually away from the edges. By further increasing the indium concentration (up to 100%), plastic deformation relaxes most of the strain energy density of the film, which prevents formation of instabilities in the film. Hence, in this case, islands are only formed near the walls.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Assessing effects of permafrost thaw on C fluxes based on multiyear modeling across a permafrost thaw gradient at Stordalen, Sweden

Northern peatlands in permafrost regions contain a large amount of organic carbon (C) in the soil. Climate warming and associated permafrost degradation are expected to have significant impacts on the C balance of these ecosystems, but the magnitude is uncertain. We incorporated a permafrost model, Northern Ecosystem Soil Temperature (NEST), into a biogeochemical model, DeNitrification-DeComposition (DNDC), to model C dynamics in high-latitude peatland ecosystems. The enhanced model was applied to assess effects of permafrost thaw on C fluxes of a subarctic peatland at Stordalen, Sweden. DNDC simulated soil freeze–thaw dynamics, net ecosystem exchange of CO 2 (NEE), and CH 4 fluxes across three typical land cover types, which represent a gradient in the process of ongoing permafrost thaw at Stordalen. Model results were compared with multiyear field measurements, and the validation indicates that DNDC was able to simulate observed differences in seasonal soil thaw, NEE, and CH 4 fluxes across the three land cover types. Consistent with the results from field studies, the modeled C fluxes across the permafrost thaw gradient demonstrate that permafrost thaw and the associated changes in soil hydrology and vegetation not only increase net uptake of C from the atmosphere but also increase the annual to decadal radiative forcing impacts on climate due to increased CH 4 emissions. This study indicates the potential of utilizing biogeochemical models, such as DNDC, to predict the soil thermal regime in permafrost areas and to investigate impacts of permafrost thaw on ecosystem C fluxes after incorporating a permafrost component into the model framework.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2014

Suppression of Upsilon production in d + Au and Au + Au collisions at root s(NN) = 200 GeV (vol 735, pg 127, 2014)

We report measurements of Υ meson production in p + p, d +Au, and Au+Aucollisions using the STAR detector at RHIC. We compare the Υ yield to the measured cross section in p + p collisions in order to quantify any modifications of the yield in cold nuclear matter using d +Au data and in hot nuclear matter using Au+Au data separated into three centrality classes. Our p +p measurement is based on three times the statistics of our previous result. We obtain a nuclear modification factor for Υ (1S + 2S + 3S) in the rapidity range |y| < 1 in d + Aucollisions of RdAu = 0.79 ± 0.24(stat.) ± 0.03(syst.) ± 0.10(p + p syst.). A comparison with models including shadowing and initial state parton energy loss indicates the presence of additional cold-nuclear matter suppression. Similarly, in the top 10% most-central Au + Au collisions, we measure a nuclear modification factor of R AA = 0.49 ±0.1(stat.) ±0.02(syst.) ±0.06(p + p syst.), which is a larger suppression factor than that seen in cold nuclear matter. Our results are consistent with complete suppression of excited-state Υ mesons in Au + Aucollisions. The additional suppression in Au + Au is consistent with the level expected in model calculations that include the presence of a hot, deconfined Quark–Gluon Plasma. However, understanding the suppression seen in d + Au is still needed before any definitive statements about the nature of the suppression in Au + Au can be made.

Quarkonium in-medium↗
DOE OSTI2014

Note: Design and initial results of a multi-pulsed intense electron beam source

A multi-pulsed intense electron beam source is introduced, including the design and the initial experimental results. The source can generate a burst of three pulses of intense electron beams with energy of 2–3 MeV and beam intensities of around 2.5 kA. An inductive adder is chosen to generate the pulsed diode voltages and a dispenser cathode is chosen to emit electron beams. The test results indicate that the design of the source is reliable. The multi-pulsed diode voltage is up to 2.5 MV and the beam intensities are more than 2 kA at the exit of the source with small variation.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2013

Measurement of J/ψ Azimuthal Anisotropy in Au+Au Collisions at √s NN =200 GeV

The measurement of J/ψ azimuthal anisotropy is presented as a function of transverse momentum for different centralities in Au+Au collisions at √s NN>/sub>=200 GeV. The measured J/ψ elliptic flow is consistent with zero within errors for transverse momentum between 2 and 10 GeV/c. Our measurement suggests that J/ψ particles with relatively large transverse momenta are not dominantly produced by coalescence from thermalized charm quarks, when comparing to model calculations.

Adamczyk, L.↗