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Cheng, J.

Publications and source records attributed to Cheng, J..

At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Measurement of elliptic flow of light nuclei at s N N = 200 , 62.4, 39, 27, 19.6, 11.5, and 7.7 GeV at the BNL Relativistic Heavy Ion Collider

Here we present measurements of second-order azimuthal anisotropy ( v 2 ) at midrapidity ( |y| < 1.0 ) for light nuclei d , t , 3 He (for $\sqrt{s}$$_{NN}$ = 200 , 62.4, 39, 27, 19.6, 11.5, and 7.7 GeV) and antinuclei$\bar{d}$ ( $\sqrt{s}$$_{NN}$ = 200 , 62.4, 39, 27, and 19.6 GeV) and 3 ¯¯¯¯¯ He ( $\sqrt{s}$$_{NN}$ = 200 GeV) in the STAR (Solenoidal Tracker at RHIC) experiment. The v 2 for these light nuclei produced in heavy-ion collisions is compared with those for p and $\bar{p}$. We observe mass ordering in nuclei v 2 ( p T ) at low transverse momenta ( p T < 2.0 GeV/c). We also find a centrality dependence of v 2 for d and $\bar{d}$ . The magnitude of v 2 for t and 3 He agree within statistical errors. Light-nuclei v 2 are compared with predictions from a blast-wave model. Atomic mass number ( A ) scaling of light-nuclei v 2 (p T ) seems to hold for p T / A < 1.5 GeV/c . Results on light-nuclei v 2 from a transport-plus-coalescence model are consistent with the experimental measurements.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Beam-energy dependence of charge balance functions from Au + Au collisions at energies available at the BNL Relativistic Heavy Ion Collider

Balance functions have been measured in terms of relative pseudorapidity ( Δη ) for charged particle pairs at the BNL Relativistic Heavy Ion Collider (RHIC) from Au + Au collisions at $\sqrt{s}$$_{NN}$ = 7.7 GeV to 200 GeV using the STAR detector. These results are compared with balance functions measured at the CERN Large Hadron Collider from Pb + Pb collisions at $\sqrt{s}$$_{NN}$ = 2.76 TeV by the ALICE Collaboration. The width of the balance function decreases as the collisions become more central and as the beam energy is increased. In contrast, the widths of the balance functions calculated using shuffled events show little dependence on centrality or beam energy and are larger than the observed widths. Balance function widths calculated using events generated by UrQMD are wider than the measured widths in central collisions and show little centrality dependence. The measured widths of the balance functions in central collisions are consistent with the delayed hadronization of a deconfined quark gluon plasma (QGP). Finally, the narrowing of the balance function in central collisions at $\sqrt{s}$$_{NN}$ = 7.7 GeV implies that a QGP is still being created at this relatively low energy.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Near-side azimuthal and pseudorapidity correlations using neutral strange baryons and mesons in d + Au , Cu + Cu, and Au + Au collisions at s N N = 200 GeV

Here we present measurements of the near side of triggered di-hadron correlations using neutral strange baryons ( $Λ,\overline{Λ}$) and mesons (K$0\atop{S}$ ) at intermediate transverse momentum (3 < pT< 6 GeV/c) to look for possible flavor and baryon-meson dependence. This study is performed in d+Au, Cu+Cu, and Au+Au collisions at $\sqrt{s}$$_{NN}$ = 200 GeV measured by the STAR experiment at RHIC. The near-side di-hadron correlation contains two structures, a peak which is narrow in azimuth and pseudorapidity consistent with correlations from jet fragmentation, and a correlation in azimuth which is broad in pseudorapidity. The particle composition of the jet-like correlation is determined using identified associated particles. The dependence of the conditional yield of the jet-like correlation on the trigger particle momentum, associated particle momentum, and centrality for correlations with unidentified trigger particles are presented. The neutral strange particle composition in jet-like correlations with unidentified charged particle triggers is not well described by PYTHIA. However, the yield of unidentified particles in jet-like correlations with neutral strange particle triggers is described reasonably well by the same model.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Measurement of the Transverse Single-Spin Asymmetry in p ↑ + p → W ± / Z 0 at RHIC

In this paper, we present the measurement of the transverse single-spin asymmetry of weak boson production in transversely polarized proton-proton collisions at $\sqrt{s}$ = 500 GeV by the STAR experiment at RHIC. The measured observable is sensitive to the Sivers function, one of the transverse-momentum-dependent parton distribution functions, which is predicted to have the opposite sign in proton-proton collisions from that observed in deep inelastic lepton-proton scattering. In conclusion, these data provide the first experimental investigation of the nonuniversality of the Sivers function, fundamental to our understanding of QCD.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Beam Energy Dependence of the Third Harmonic of Azimuthal Correlations in Au+Au Collisions at RHIC

In this paper, we present results from a harmonic decomposition of two-particle azimuthal correlations measured with the STAR detector in Au + Au collisions for energies ranging from √sNN = 7.7 to 200 GeV. The third harmonic v$2\atop{3}${ 2 } = , where Φ1 - Φ2 is the angular difference in azimuth, is studied as a function of the pseudorapidity difference between particle pairs Δη = η1-η2 . Nonzero v$2\atop{3}${ 2 } is directly related to the previously observed large- Δη narrow- ΔΦ ridge correlations and has been shown in models to be sensitive to the existence of a low viscosity quark gluon plasma phase. For sufficiently central collisions, v$2\atop{3}${ 2 } persist down to an energy of 7.7 GeV, suggesting that quark gluon plasma may be created even in these low energy collisions. In peripheral collisions at these low energies, however, v$2\atop{3}${ 2 } is consistent with zero. Finally, when scaled by the pseudorapidity density of charged-particle multiplicity per participating nucleon pair, v$2\atop{3}${ 2 } for central collisions shows a minimum near √sNN = 20 GeV .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

An investigation of the optical properties and water splitting potential of the coloured metallic perovskites Sr{sub 1−x}Ba{sub x}MoO{sub 3}

The solid solution Sr{sub 1−x}Ba{sub x}MoO{sub 3} (x=0.00, 0.025, 0.050, 0.075, 0.100 and 1.00) has been synthesised. Rietveld refinement of X-ray diffraction data shows that all materials crystallise with cubic (Pm-3m) symmetry and that a miscibility gap exists from x=0.1–1.0. The optical properties of the metallic perovskites Sr{sub 1−x}Ba{sub x}MoO{sub 3} have been investigated by a combination of UV–vis spectroscopy and density functional theory (DFT). Upon increasing x from 0 to 1 in Sr{sub 1−x}Ba{sub x}MoO{sub 3} there is a reduction in the measured band gap from 2.20 eV to 2.07 eV. The measured band gap is attributed to the electronic transition from the Mo 4d t{sub 2g} band to the e{sub g} band. The potential of SrMoO{sub 3} and BaMoO{sub 3} as water-splitting photocatalysts was explored but there was no evidence of hydrogen or oxygen evolution, even with the presence of a Pt co-catalyst. - Graphical abstract: Ultraviolet–visible absorbance spectra (converted from diffuse reflectance spectra) for SrMoO{sub 3} and BaMoO{sub 3}. - Highlights: • The solid solution Sr{sub 1-x}Ba{sub x}MoO{sub 3} has been synthesised. • A miscibility gap exists from x=0.1–1.0 in Sr{sub 1−x}Ba{sub x}MoO{sub 3.} • Upon increasing x from 0 to 1 in Sr{sub 1−x}Ba{sub x}MoO{sub 3} there is a reduction in the measured band gap from 2.20 eV to 2.07 eV. • The potential of SrMoO{sub 3} and BaMoO{sub 3} as water-splitting photocatalysts was explored but there was no evidence of hydrogen or oxygen evolution, even with the presence of a Pt co-catalyst.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Centrality and Transverse Momentum Dependence of Elliptic Flow of Multistrange Hadrons and φ Meson in Au + Au Collisions at s N N = 200 GeV

In this paper, we present high precision measurements of elliptic flow near midrapidity (|y|<1.0) for multistrange hadrons and φ meson as a function of centrality and transverse momentum in Au+Au collisions at center of mass energy $\sqrt{sNN}$=200 GeV. We observe that the transverse momentum dependence of φ and Ωv 2 is similar to that of π and p, respectively, which may indicate that the heavier strange quark flows as strongly as the lighter up and down quarks. This observation constitutes a clear piece of evidence for the development of partonic collectivity in heavy-ion collisions at the top RHIC energy. Number of constituent quark scaling is found to hold within statistical uncertainty for both 0%-30% and 30%-80% collision centrality. Finally, there is an indication of the breakdown of previously observed mass ordering between φ and proton v 2 at low transverse momentum in the 0%-30% centrality range, possibly indicating late hadronic interactions affecting the proton v 2 .

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Centrality dependence of identified particle elliptic flow in relativistic heavy ion collisions at s N N = 7.7 – 62.4 GeV

Here, elliptic flow (v 2 ) values for identified particles at midrapidity in Au + Au collisions measured by the STAR experiment in the Beam Energy Scan at the Relativistic Heavy Ion Collider at √s NN = 7.7–62.4 GeV are presented for three centrality classes. The centrality dependence and the data at √s NN = 14.5 GeV are new. Except at the lowest beam energies, we observe a similar relative v 2 baryon-meson splitting for all centrality classes which is in agreement within 15% with the number-of-constituent quark scaling. The larger v 2 for most particles relative to antiparticles, already observed for minimum bias collisions, shows a clear centrality dependence, with the largest difference for the most central collisions. Also, the results are compared with a multiphase transport (AMPT) model and fit with a blast wave model.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

The detector system of the Daya Bay reactor neutrino experiment

The Daya Bay experiment was the first to report simultaneous measurements of reactor antineutrinos at multiple baselines leading to the discovery of ν¯e oscillations over km-baselines. Subsequent data has provided the world's most precise measurement of sin 2 2θ 13 and the effective mass splitting Δm 2 ee . The experiment is located in Daya Bay, China where the cluster of six nuclear reactors is among the world's most prolific sources of electron antineutrinos. Multiple antineutrino detectors are deployed in three underground water pools at different distances from the reactor cores to search for deviations in the antineutrino rate and energy spectrum due to neutrino mixing. Instrumented with photomultiplier tubes, the water pools serve as shielding against natural radioactivity from the surrounding rock and provide efficient muon tagging. Arrays of resistive plate chambers over the top of each pool provide additional muon detection. The antineutrino detectors were specifically designed for measurements of the antineutrino flux with minimal systematic uncertainty. Relative detector efficiencies between the near and far detectors are known to better than 0.2%. With the unblinding of the final two detectors’ baselines and target masses, a complete description and comparison of the eight antineutrino detectors can now be presented. This study describes the Daya Bay detector systems, consisting of eight antineutrino detectors in three instrumented water pools in three underground halls, and their operation through the first year of eight detector data-taking.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Measurement of interaction between antiprotons

In this paper, one of the primary goals of nuclear physics is to understand the force between nucleons, which is a necessary step for understanding the structure of nuclei and how nuclei interact with each other. Rutherford discovered the atomic nucleus in 1911, and the large body of knowledge about the nuclear force that has since been acquired was derived from studies made on nucleons or nuclei. Although antinuclei up to antihelium-4 have been discovered and their masses measured, little is known directly about the nuclear force between antinucleons. Here, we study antiproton pair correlations among data collected by the STAR experiment at the Relativistic Heavy Ion Collider (RHIC), where gold ions are collided with a centre-of-mass energy of 200 gigaelectronvolts per nucleon pair. Antiprotons are abundantly produced in such collisions, thus making it feasible to study details of the antiproton–antiproton interaction. By applying a technique similar to Hanbury Brown and Twiss intensity interferometry, we show that the force between two antiprotons is attractive. In addition, we report two key parameters that characterize the corresponding strong interaction: the scattering length and the effective range of the interaction. Our measured parameters are consistent within errors with the corresponding values for proton–proton interactions. Our results provide direct information on the interaction between two antiprotons, one of the simplest systems of antinucleons, and so are fundamental to understanding the structure of more-complex antinuclei and their properties.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

New measurement of antineutrino oscillation with the full detector configuration at Daya Bay

We report a new measurement of electron antineutrino disappearance using the fully constructed Daya Bay Reactor Neutrino Experiment. The final two of eight antineutrino detectors were installed in the summer of 2012. Including the 404 days of data collected from October 2012 to November 2013 resulted in a total exposure of 6.9×10 5 GW th ton days, a 3.6 times increase over our previous results. Improvements in energy calibration limited variations between detectors to 0.2%. Removal of six 241 Am- 13 C radioactive calibration sources reduced the background by a factor of 2 for the detectors in the experimental hall furthest from the reactors. Direct prediction of the antineutrino signal in the far detectors based on the measurements in the near detectors explicitly minimized the dependence of the measurement on models of reactor antineutrino emission. The uncertainties in our estimates of 2 sin2θ 13 and |Δm 2 ee | were halved as a result of these improvements. An analysis of the relative antineutrino rates and energy spectra between detectors gave 2 sin2θ 13 =0.084±0.005 and |Δm 2 ee |=(2.42±0.11)×10 –3 eV 2 in the three-neutrino framework.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Measurements of dielectron production in Au + Au collisions at s N N = 200 GeV from the STAR experiment

We report on measurements of dielectron (e⁺e⁻) production in Au+Au collisions at a center-of-mass energy of 200 GeV per nucleon-nucleon pair using the STAR detector at RHIC. Systematic measurements of the dielectron yield as a function of transverse momentum (p T ) and collision centrality show an enhancement compared to a cocktail simulation of hadronic sources in the low invariant-mass region (M ee < 1GeV/c 2 ). This enhancement cannot be reproduced by the ρ-meson vacuum spectral function. In minimum-bias collisions, in the invariant-mass range of 0.30 – 0.76GeV/c², integrated over the full p T acceptance, the enhancement factor is 1.76±0.06(stat.)±0.26(sys.)±0.29(cocktail). The enhancement factor exhibits weak centrality and p T dependence in STAR's accessible kinematic regions, while the excess yield in this invariant-mass region as a function of the number of participating nucleons follows a power-law shape with a power of 1.44±0.10. Models that assume an in-medium broadening of the ρ-meson spectral function consistently describe the observed excess in these measurements. In addition, we report on measurements of ω- and Φ-meson production through their e⁺e⁻ decay channel. These measurements show good agreement with Tsallis blast-wave model predictions, as well as, in the case of the Φ meson, results through its K⁺K⁻ decay channel. In the intermediate invariant-mass region (1.1 < M ee < 3GeV/c²), we investigate the spectral shapes from different collision centralities. Physics implications for possible in-medium modification of charmed hadron production and other physics sources are discussed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
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↗