717 research outputs found
Improved cosmological constraints on the curvature and equation of state of dark energy
We apply the Constitution compilation of 397 supernova Ia, the baryon
acoustic oscillation measurements including the parameter, the distance
ratio and the radial data, the five-year Wilkinson microwave anisotropy probe
and the Hubble parameter data to study the geometry of the universe and the
property of dark energy by using the popular Chevallier-Polarski-Linder and
Jassal-Bagla-Padmanabhan parameterizations. We compare the simple
method of joined contour estimation and the Monte Carlo Markov chain method,
and find that it is necessary to make the marginalized analysis on the error
estimation. The probabilities of and in the
Chevallier-Polarski-Linder model are skew distributions, and the marginalized
errors are ,
, , and
. For the Jassal-Bagla-Padmanabhan model, the
marginalized errors are ,
, , and
. The equation of state parameter of dark energy
is negative in the redshift range at more than level.
The flat CDM model is consistent with the current observational data
at the level.Comment: 10 figures, 12 pages, Classical and Quantum Gravity in press; v2 to
match the pulished versio
Synthesis of Mesoporous Silica@Co–Al Layered Double Hydroxide Spheres: Layer-by-Layer Method and Their Effects on the Flame Retardancy of Epoxy Resins
Hierarchical mesoporous silica@Co–Al layered double hydroxide (m-SiO2@Co–Al LDH) spheres were prepared through a layer-by-layer assembly process, in order to integrate their excellent physical and chemical functionalities. TEM results depicted that, due to the electrostatic potential difference between m-SiO2 and Co–Al LDH, the synthetic m-SiO2@Co–Al LDH hybrids exhibited that m-SiO2 spheres were packaged by the Co–Al LDH nanosheets. Subsequently, the m-SiO2@Co–Al LDH spheres were incorporated into epoxy resin (EP) to prepare specimens for investigation of their flame-retardant performance. Cone results indicated that m-SiO2@Co–Al LDH incorporated obviously improved fire retardant of EP. A plausible mechanism of fire retardant was hypothesized based on the analyses of thermal conductivity, char residues, and pyrolysis fragments. Labyrinth effect of m-SiO2 and formation of graphitized carbon char catalyzed by Co–Al LDH play pivotal roles in the flame retardance enhancement
Observation of a near-threshold enhancement in th p pbar mass spectrum from radiative J/psi-->gamma p pbar decays
We observe a narrow enhancement near 2mp in the invariant mass spectrum of
ppbar pairs from radiative J/psi-->gamma ppbar decays. The enhancement can be
fit with either an S- or P-wave Breit Wigner fuction. In the case of the S-wave
fit, the peak mass is below the 2mp threshold and the full width is less than
30 MeV. These mass and width values are not consistent with the properties of
any known meson resonance.Comment: 5 pages, 4 figures, submitted to Phys. Rev. Let
JUNO Conceptual Design Report
The Jiangmen Underground Neutrino Observatory (JUNO) is proposed to determine
the neutrino mass hierarchy using an underground liquid scintillator detector.
It is located 53 km away from both Yangjiang and Taishan Nuclear Power Plants
in Guangdong, China. The experimental hall, spanning more than 50 meters, is
under a granite mountain of over 700 m overburden. Within six years of running,
the detection of reactor antineutrinos can resolve the neutrino mass hierarchy
at a confidence level of 3-4, and determine neutrino oscillation
parameters , , and to
an accuracy of better than 1%. The JUNO detector can be also used to study
terrestrial and extra-terrestrial neutrinos and new physics beyond the Standard
Model. The central detector contains 20,000 tons liquid scintillator with an
acrylic sphere of 35 m in diameter. 17,000 508-mm diameter PMTs with high
quantum efficiency provide 75% optical coverage. The current choice of
the liquid scintillator is: linear alkyl benzene (LAB) as the solvent, plus PPO
as the scintillation fluor and a wavelength-shifter (Bis-MSB). The number of
detected photoelectrons per MeV is larger than 1,100 and the energy resolution
is expected to be 3% at 1 MeV. The calibration system is designed to deploy
multiple sources to cover the entire energy range of reactor antineutrinos, and
to achieve a full-volume position coverage inside the detector. The veto system
is used for muon detection, muon induced background study and reduction. It
consists of a Water Cherenkov detector and a Top Tracker system. The readout
system, the detector control system and the offline system insure efficient and
stable data acquisition and processing.Comment: 328 pages, 211 figure
Transverse energy production and charged-particle multiplicity at midrapidity in various systems from to 200 GeV
Measurements of midrapidity charged particle multiplicity distributions,
, and midrapidity transverse-energy distributions,
, are presented for a variety of collision systems and energies.
Included are distributions for AuAu collisions at ,
130, 62.4, 39, 27, 19.6, 14.5, and 7.7 GeV, CuCu collisions at
and 62.4 GeV, CuAu collisions at
GeV, UU collisions at GeV,
Au collisions at GeV, HeAu collisions at
GeV, and collisions at
GeV. Centrality-dependent distributions at midrapidity are presented in terms
of the number of nucleon participants, , and the number of
constituent quark participants, . For all collisions
down to GeV, it is observed that the midrapidity data
are better described by scaling with than scaling with . Also presented are estimates of the Bjorken energy density,
, and the ratio of to ,
the latter of which is seen to be constant as a function of centrality for all
systems.Comment: 706 authors, 32 pages, 20 figures, 34 tables, 2004, 2005, 2008, 2010,
2011, and 2012 data. v2 is version accepted for publication in Phys. Rev.
Measurement of long-range angular correlation and quadrupole anisotropy of pions and (anti)protons in central Au collisions at =200 GeV
We present azimuthal angular correlations between charged hadrons and energy
deposited in calorimeter towers in central Au and minimum bias
collisions at GeV. The charged hadron is measured at
midrapidity , and the energy is measured at large rapidity
(, Au-going direction). An enhanced near-side angular
correlation across 2.75 is observed in Au collisions.
Using the event plane method applied to the Au-going energy distribution, we
extract the anisotropy strength for inclusive charged hadrons at
midrapidity up to GeV/. We also present the measurement of
for identified and (anti)protons in central Au collisions,
and observe a mass-ordering pattern similar to that seen in heavy ion
collisions. These results are compared with viscous hydrodynamic calculations
and measurements from Pb at TeV. The magnitude of
the mass-ordering in Au is found to be smaller than that in Pb
collisions, which may indicate smaller radial flow in lower energy Au
collisions.Comment: 424 authors, 8 pages, and 4 figures. v2 is version accepted for
publication in Phys. Rev. Lett. Published version will be at
http://www.phenix.bnl.gov/phenix/WWW/info/pp1/161/ Plain text data tables
will be at http://www.phenix.bnl.gov/papers.htm
Cold-nuclear-matter effects on heavy-quark production at forward and backward rapidity in d+Au collisions at sqrt(s_NN)=200 GeV
The PHENIX experiment has measured open heavy-flavor production via
semileptonic decay muons over the transverse momentum range 1 < pT < 6 GeV/c at
forward and backward rapidity (1.4 < |y| < 2.0) in d+Au and p+p collisions at
?sNN = 200 GeV. In central d+Au collisions an enhancement (suppression) of
heavy-flavor muon production is observed at backward (forward) rapidity
relative to the yield in p+p collisions scaled by the number of binary
collisions. Modification of the gluon density distribution in the Au nucleus
contributes in terms of anti-shadowing enhancement and shadowing suppression;
however, the enhancement seen at backward rapidity exceeds expectations from
this effect alone. These results, implying an important role for additional
cold nuclear matter effects, serves as a key baseline for heavy-quark
measurements in A+A collisions and in constraining the magnitude of charmonia
breakup effects at the Relativistic Heavy Ion Collider and the Large Hadron
Collider.Comment: 424 authors, 69 insitutions, 8 pages, 4 figures. Submitted to
Physical Review Letters. Plain text data tables for the points plotted in
figures for this and previous PHENIX publications are (or will be) publicly
available at http://www.phenix.bnl.gov/papers.htm
Upsilon (1S+2S+3S) production in d+Au and p+p collisions at sqrt(s_NN)=200 GeV and cold-nuclear matter effects
The three Upsilon states, Upsilon(1S+2S+3S), are measured in d+Au and p+p
collisions at sqrt(s_NN)=200 GeV and rapidities 1.2<|y|<2.2 by the PHENIX
experiment at the Relativistic Heavy-Ion Collider. Cross sections for the
inclusive Upsilon(1S+2S+3S) production are obtained. The inclusive yields per
binary collision for d+Au collisions relative to those in p+p collisions
(R_dAu) are found to be 0.62 +/- 0.26 (stat) +/- 0.13 (syst) in the gold-going
direction and 0.91 +/- 0.33 (stat) +/- 0.16 (syst) in the deuteron-going
direction. The measured results are compared to a nuclear-shadowing model,
EPS09 [JHEP 04, 065 (2009)], combined with a final-state breakup cross section,
sigma_br, and compared to lower energy p+A results. We also compare the results
to the PHENIX J/psi results [Phys. Rev. Lett. 107, 142301 (2011)]. The rapidity
dependence of the observed Upsilon suppression is consistent with lower energy
p+A measurements.Comment: 495 authors, 11 pages, 9 figures, 5 tables. Submitted to Phys. Rev.
C. Plain text data tables for the points plotted in figures for this and
previous PHENIX publications are (or will be) publicly available at
http://www.phenix.bnl.gov/papers.htm
meson production in Au collisions at GeV
The PHENIX experiment has measured meson production in Au
collisions at GeV using the dimuon and dielectron decay
channels. The meson is measured in the forward (backward) -going
(Au-going) direction, () in the transverse-momentum
() range from 1--7 GeV/, and at midrapidity in the
range below 7 GeV/. The meson invariant yields and
nuclear-modification factors as a function of , rapidity, and centrality
are reported. An enhancement of meson production is observed in the
Au-going direction, while suppression is seen in the -going direction, and
no modification is observed at midrapidity relative to the yield in
collisions scaled by the number of binary collisions. Similar behavior was
previously observed for inclusive charged hadrons and open heavy flavor
indicating similar cold-nuclear-matter effects.Comment: 484 authors, 16 pages, 12 figures, 6 tables. v1 is the version
accepted for publication in Phys. Rev. C. Data tables for the points plotted
in the figures are given in the paper itsel
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