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Deng, J.

Publications and source records attributed to Deng, J..

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Harmonic decomposition of three-particle azimuthal correlations at energies available at the BNL Relativistic Heavy Ion Collider

Here, we present measurements of three-particle correlations for various harmonics in Au+Au collisions at energies ranging from √ s NN=7.7 to 200 GeV using the STAR detector. The quantity < cos(mΦ 1 +nΦ 2 –(m+n)Φ 3 ) >, with Φ being the azimuthal angles of the particles is evaluated as a function of √ s NN, collision centrality, transverse momentum, p T , pseudorapidity difference, Δη, and harmonics (m and n). These data provide detailed information on global event properties such as the three-dimensional structure of the initial overlap region, the expansion dynamics of the matter produced in the collisions, and the transport properties of the medium. A strong dependence on Δη is observed for most harmonic combinations, which is consistent with breaking of longitudinal boost invariance. An interesting energy dependence is observed when one of the harmonics m,n, or m+n is equal to two, for which the correlators are dominated by the two-particle correlations relative to the second-harmonic event plane. These measurements can be used to constrain models of heavy-ion collisions over a wide range of temperature and baryon chemical potential.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

Challenges and Opportunities with Highly Brilliant X-ray Sources for multi-Modal in-Situ and Operando Characterization of Solar Cells

The generation of electricity is one of the great challenges of our time, and its success shall be measured by the sustainability from ecological, economical, and social points of view. The advent of photovoltaics has led to a dramatic decrease of the levelized cost of energy (LCOE) such that it has not only reached grid parity in many countries but is often the most competitive energy source.

Stuckelberger, M. E.↗
DOE OSTI2018

Measurement of the H Λ 3 lifetime in Au+Au collisions at the BNL Relativistic Heavy Ion Collider [Measurement of the H Λ 3 lifetime in Au+Au collisions at the Relativistic Heavy Ion Collider]

Here, an improved measurement of the 3 Λ H lifetime is presented. In this paper, the mesonic decay modes 3 Λ H → 3 He + π – and 3 Λ H → d + p + π – are used to reconstruct the 3 Λ H from Au+Au collision data collected by the STAR collaboration at Relativistic Heavy Ion Collider (RHIC). A minimum χ2 estimation is used to determine the lifetime of τ = 142 +24 –21 (stat.) ± 29 (syst.) ps. This lifetime is about 50% shorter than the lifetime τ = 263 ± 2 ps of a free Λ, indicating strong hyperon-nucleon interaction in the hypernucleus system. The branching ratios of the mesonic decay channels are also determined to satisfy B.R. ( 3 He+π – )/( B.R. ( 3 He+π – ) + B.R. (d+p+π – ) ) = 0.32 ± 0.05 (stat.) ± 0.08 (syst.). Our ratio result favors the assignment J( 3 Λ H) = 1/2 over J( 3 Λ H) = 3/2. These measurements will help to constrain models of hyperon-baryon interactions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Coherent diffractive photoproduction of ρ 0 mesons on gold nuclei at 200 GeV/nucleon-pair at the Relativistic Heavy Ion Collider

Here, the STAR Collaboration reports on the photoproduction of π + π - pairs in goldgold collisions at a center-of-mass energy of 200 GeV/nucleon-pair. These pion pairs are produced when a nearly-real photon emitted by one ion scatters from the other ion. We fit the π + π - invariant mass spectrum with a combination of 0 and ! resonances and a direct π + π - continuum. This is the first observation of the ! in ultra-peripheral collisions, and the first measurement of ρ - ω interference at energies where photoproduction is dominated by Pomeron exchange.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Bulk properties of the medium produced in relativistic heavy-ion collisions from the beam energy scan program

We present measurements of bulk properties of the matter produced in Au+Au collisions at $\sqrt{s}$$_ {NN}$= 7.7, 11.5, 19.6, 27, and 39 GeV using identified hadrons (π ± , K ± , p, and $\bar{p}$) from the STAR experiment in the Beam Energy Scan (BES) Program at the Relativistic Heavy Ion Collider (RHIC). Midrapidity (| y | < 0.1) results for multiplicity densities dN / dy, average transverse momenta $\langle$pT$\rangle$, and particle ratios are presented. The chemical and kinetic freeze-out dynamics at these energies are discussed and presented as a function of collision centrality and energy. These results constitute the systematic measurements of bulk properties of matter formed in heavy-ion collisions over a broad range of energy (or baryon chemical potential) at RHIC.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Measurements of jet quenching with semi-inclusive hadron+jet distributions in Au + Au collisions at s N N = 200 GeV

Here, the STAR Collaboration reports the measurement of semi-inclusive distributions of charged-particle jets recoiling from a high transverse momentum hadron trigger, in central and peripheral Au+Au collisions at √ s NN = 200 GeV. Charged jets are reconstructed with the anti-k T algorithm for jet radii R between 0.2 and 0.5 and with low infrared cutoff of track constituents (p T > 0.2 GeV/c). A novel mixed-event technique is used to correct the large uncorrelated background present in heavy ion collisions. Corrected recoil jet distributions are reported at midrapidity, for charged-jet transverse momentum p ch T,jet < 30 GeV/c. Comparison is made to similar measurements for Pb+Pb collisions at √s = 2.76 TeV, to calculations for p+p collisions at √s = 200 GeV based on the pythia Monte Carlo generator and on a next-to-leading order perturbative QCD approach, and to theoretical calculations incorporating jet quenching. The recoil jet yield is suppressed in central relative to peripheral collisions, with the magnitude of the suppression corresponding to medium-induced charged energy transport out of the jet cone of 2.8 ± 0.2(stat) ± 1.5(sys) GeV/c, for 10 < p ch T,jet < 20 GeV/c and R = 0.5. No medium-induced change in jet shape is observed for R < 0.5. The azimuthal distribution of low-p ch T,jet recoil jets may be enhanced at large azimuthal angles to the trigger axis, due to scattering off quasiparticles in the hot QCD medium. As a result, measurement of this distribution gives a 90% statistical confidence upper limit to the yield enhancement at large deflection angles in central Au + Au collisions of 50 ± 30(sys)% of the large-angle yield in p+p collisions predicted by pythia.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Dijet imbalance measurements in Au + Au and p p collisions at s N N = 200 GeV at STAR

In this paper, we report the first dijet transverse momentum asymmetry measurements from Au + Au and pp collisions at RHIC. The two highest-energy back-to-back jets reconstructed from fragments with transverse momenta above 2 GeV/c display a significantly higher momentum imbalance in heavy-ion collisions than in the pp reference. Finally, when reexamined with correlated soft particles included, we observe that these dijets then exhibit a unique new feature—momentum balance is restored to that observed in pp for a jet resolution parameter of R = 0.4, while rebalancing is not attained with a smaller value of R = 0.2.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Global Λ hyperon polarization in nuclear collisions

The extreme energy densities generated by ultra-relativistic collisions between heavy atomic nuclei produce a state of matter that behaves surprisingly like a fluid, with exceptionally high temperature and low viscosity. Non-central collisions have angular momenta of the order of 1,000ћ, and the resulting fluid may have a strong vortical structure that must be understood to describe the fluid properly. The vortical structure is also of particular interest because the restoration of fundamental symmetries of quantum chromodynamics is expected to produce novel physical effects in the presence of strong vorticity. But, no experimental indications of fluid vorticity in heavy ion collisions have yet been found. Since vorticity represents a local rotational structure of the fluid, spin–orbit coupling can lead to preferential orientation of particle spins along the direction of rotation. Here we present measurements of an alignment between the global angular momentum of a non-central collision and the spin of emitted particles (in this case the collision occurs between gold nuclei and produces Λ baryons), revealing that the fluid produced in heavy ion collisions is the most vortical system so far observed. (At high energies, this fluid is a quark–gluon plasma.) We find that Λ and hyperons show a positive polarization of the order of a few per cent, consistent with some hydrodynamic predictions. (A hyperon is a particle composed of three quarks, at least one of which is a strange quark; the remainder are up and down quarks, found in protons and neutrons.) A previous measurement that reported a null result, that is, zero polarization, at higher collision energies is seen to be consistent with the trend of our observations, though with larger statistical uncertainties. Furthermore, these data provide experimental access to the vortical structure of the nearly ideal liquid created in a heavy ion collision and should prove valuable in the development of hydrodynamic models that quantitatively connect observations to the theory of the strong force.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Measurement of D 0 Azimuthal Anisotropy at Midrapidity in Au + Au Collisions at s N N = 200 GeV

In this paper, we report the first measurement of the elliptic anisotropy (v2) of the charm meson D 0 at midrapidity (|y| < 1) in Au + Au collisions at $\sqrt{s}$$_ {NN}$ = 200 GeV. The measurement was conducted by the STAR experiment at RHIC utilizing a new high-resolution silicon tracker. The measured D 0 v 2 in 0%–80% centrality Au + Au collisions can be described by a viscous hydrodynamic calculation for a transverse momentum (p T ) of less than 4 GeV/c . The D 0 v 2 as a function of transverse kinetic energy (m T - m 0 , where m T = $\sqrt{p}$$2\atop{T}$ + m$2\atop{0}$) is consistent with that of light mesons in 10%–40% centrality Au + Au collisions. These results suggest that charm quarks have achieved local thermal equilibrium with the medium created in such collisions. In conclusion, several theoretical models, with the temperature-dependent, dimensionless charm spatial diffusion coefficient (2πTD s ) in the range of ~2–12 , are able to simultaneously reproduce our D 0 v 2 result and our previously published results for the D 0 nuclear modification factor.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Energy dependence of J / ψ production in Au + Au collisions at s N N = 39 , 62.4 and 200 GeV

The inclusive J / ψ transverse momentum spectra and nuclear modification factors are reported at mid-rapidity ( | y | < 1.0 ) in Au + Au collisions at s N N = 39, 62.4 and 200 GeV taken by the STAR experiment. A suppression of J / ψ production, with respect to the production in p + p scaled by the number of binary nucleon–nucleon collisions, is observed in central Au + Au collisions at these three energies. No significant energy dependence of nuclear modification factors is found within uncertainties. The measured nuclear modification factors can be described by model calculations that take into account both suppression of direct J / ψ production due to the color screening effect and J / ψ regeneration from recombination of uncorrelated charm–anticharm quark pairs.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Measurement of the cross section and longitudinal double-spin asymmetry for dijet production in polarized p p collisions at s = 200 GeV

We report the first measurement of the longitudinal double-spin asymmetry A LL for mid-rapidity dijet production in polarized pp collisions at a center-of-mass energy of $\sqrt{s}$ = 200 GeV. The dijet cross section was measured and is shown to be consistent with next-to-leading order (NLO) perturbative QCD predictions. A LL results are presented for two distinct topologies, defined by the jet pseudorapidities, and are compared to predictions from several recent NLO global analyses. Lastly, the measured asymmetries, the first such correlation measurements, support those analyses that find positive gluon polarization at the level of roughly 0.2 over the region of Bjorken-x > 0.05.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Direct virtual photon production in Au+Au collisions at s N N = 200 GeV

We report the direct virtual photon invariant yields in the transverse momentum ranges 1 < p T < 3 GeV / c and 5 < p T < 10 GeV / c at mid-rapidity derived from the dielectron invariant mass continuum region 0.10 < M e e < 0.28 GeV / c 2 for 0–80% minimum-bias Au+Au collisions at s N N = 200 GeV . A clear excess in the invariant yield compared to the nuclear overlap function T A A scaled p + p reference is observed in the p T range 1 < p T < 3 GeV / c . For p T > 6 GeV / c the production follows T A A scaling. Model calculations with contributions from thermal radiation and initial hard parton scattering are consistent within uncertainties with the direct virtual photon invariant yield.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗