62 research outputs found
The Global Genome Biodiversity Network (GGBN) Data Standard specification
© The Author(s) 2016. Published by Oxford University Press. Page 1 of 11 This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited. The article attached is the publisher's pdf
Event-by-event correlations between () hyperon global polarization and handedness with charged hadron azimuthal separation in Au+Au collisions at from STAR
Global polarizations () of () hyperons have been
observed in non-central heavy-ion collisions. The strong magnetic field
primarily created by the spectator protons in such collisions would split the
and global polarizations (). Additionally, quantum chromodynamics (QCD) predicts
topological charge fluctuations in vacuum, resulting in a chirality imbalance
or parity violation in a local domain. This would give rise to an imbalance
() between left- and right-handed
() as well as a charge separation along the magnetic field,
referred to as the chiral magnetic effect (CME). This charge separation can be
characterized by the parity-even azimuthal correlator () and
parity-odd azimuthal harmonic observable (). Measurements of
, , and have not led to definitive
conclusions concerning the CME or the magnetic field, and has not
been measured previously. Correlations among these observables may reveal new
insights. This paper reports measurements of correlation between and
, which is sensitive to chirality fluctuations, and correlation
between and sensitive to magnetic field in Au+Au
collisions at 27 GeV. For both measurements, no correlations have been observed
beyond statistical fluctuations.Comment: 10 pages, 10 figures; paper from the STAR Collaboratio
Hyperon polarization along the beam direction relative to the second and third harmonic event planes in isobar collisions at = 200 GeV
The polarization of and hyperons along the beam
direction has been measured relative to the second and third harmonic event
planes in isobar Ru+Ru and Zr+Zr collisions at = 200 GeV. This
is the first experimental evidence of the hyperon polarization by the
triangular flow originating from the initial density fluctuations. The
amplitudes of the sine modulation for the second and third harmonic results are
comparable in magnitude, increase from central to peripheral collisions, and
show a mild dependence. The azimuthal angle dependence of the
polarization follows the vorticity pattern expected due to elliptic and
triangular anisotropic flow, and qualitatively disagree with most hydrodynamic
model calculations based on thermal vorticity and shear induced contributions.
The model results based on one of existing implementations of the shear
contribution lead to a correct azimuthal angle dependence, but predict
centrality and dependence that still disagree with experimental
measurements. Thus, our results provide stringent constraints on the thermal
vorticity and shear-induced contributions to hyperon polarization. Comparison
to previous measurements at RHIC and the LHC for the second-order harmonic
results shows little dependence on the collision system size and collision
energy.Comment: 6 pages, 5 figures, Published in Physical Review Letter
Measurement of electrons from open heavy-flavor hadron decays in Au+Au collisions at GeV with the STAR detector
We report a new measurement of the production of electrons from open
heavy-flavor hadron decays (HFEs) at mid-rapidity ( 0.7) in Au+Au
collisions at GeV. Invariant yields of HFEs are
measured for the transverse momentum range of GeV/ in
various configurations of the collision geometry. The HFE yields in head-on
Au+Au collisions are suppressed by approximately a factor of 2 compared to that
in + collisions scaled by the average number of binary collisions,
indicating strong interactions between heavy quarks and the hot and dense
medium created in heavy-ion collisions. Comparison of these results with models
provides additional tests of theoretical calculations of heavy quark energy
loss in the quark-gluon plasma
Elliptic Flow of Heavy-Flavor Decay Electrons in Au+Au Collisions at = 27 and 54.4 GeV at RHIC
We report on new measurements of elliptic flow () of electrons from
heavy-flavor hadron decays at mid-rapidity () in Au+Au collisions at
= 27 and 54.4 GeV from the STAR experiment. Heavy-flavor
decay electrons () in Au+Au collisions at =
54.4 GeV exhibit a non-zero in the transverse momentum ()
region of 2 GeV/ with the magnitude comparable to that at
GeV. The measured at 54.4 GeV is
also consistent with the expectation of their parent charm hadron
following number-of-constituent-quark scaling as other light and strange flavor
hadrons at this energy. These suggest that charm quarks gain significant
collectivity through the evolution of the QCD medium and may reach local
thermal equilibrium in Au+Au collisions at GeV. The
measured in Au+Au collisions at 27
GeV is consistent with zero within large uncertainties. The energy dependence
of for different flavor particles () shows an
indication of quark mass hierarchy in reaching thermalization in high-energy
nuclear collisions.Comment: 12 pages, 7 figures, 1 tabl
Search for the Chiral Magnetic Effect in Au+Au collisions at GeV with the STAR forward Event Plane Detectors
A decisive experimental test of the Chiral Magnetic Effect (CME) is
considered one of the major scientific goals at the Relativistic Heavy-Ion
Collider (RHIC) towards understanding the nontrivial topological fluctuations
of the Quantum Chromodynamics vacuum. In heavy-ion collisions, the CME is
expected to result in a charge separation phenomenon across the reaction plane,
whose strength could be strongly energy dependent. The previous CME searches
have been focused on top RHIC energy collisions. In this Letter, we present a
low energy search for the CME in Au+Au collisions at
GeV. We measure elliptic flow scaled charge-dependent correlators relative to
the event planes that are defined at both mid-rapidity and at
forward rapidity . We compare the results based on the
directed flow plane () at forward rapidity and the elliptic flow plane
() at both central and forward rapidity. The CME scenario is expected
to result in a larger correlation relative to than to , while
a flow driven background scenario would lead to a consistent result for both
event planes[1,2]. In 10-50\% centrality, results using three different event
planes are found to be consistent within experimental uncertainties, suggesting
a flow driven background scenario dominating the measurement. We obtain an
upper limit on the deviation from a flow driven background scenario at the 95\%
confidence level. This work opens up a possible road map towards future CME
search with the high statistics data from the RHIC Beam Energy Scan Phase-II.Comment: main: 8 pages, 5 figures; supplementary material: 2 pages, 1 figur
Measurement of and binding energy in Au+Au collisions at = 3 GeV
Measurements of mass and binding energy of and
in Au+Au collisions at GeV are
presented, with an aim to address the charge symmetry breaking (CSB) problem in
hypernuclei systems with atomic number A = 4. The binding energies
are measured to be MeV and MeV for and , respectively. The measured binding-energy difference
is MeV for ground states. Combined with
the -ray transition energies, the binding-energy difference for excited
states is MeV, which is negative and
comparable to the value of the ground states within uncertainties. These new
measurements on the binding-energy difference in A = 4 hypernuclei
systems are consistent with the theoretical calculations that result in
and present a new method for the study of CSB effect using relativistic
heavy-ion collisions.Comment: 8 pages, 5 figure
Tomography of Ultra-relativistic Nuclei with Polarized Photon-gluon Collisions
A linearly polarized photon can be quantized from the Lorentz-boosted
electromagnetic field of a nucleus traveling at ultra-relativistic speed. When
two relativistic heavy nuclei pass one another at a distance of a few nuclear
radii, the photon from one nucleus may interact through a virtual
quark-antiquark pair with gluons from the other nucleus forming a short-lived
vector meson (e.g. ). In this experiment, the polarization was
utilized in diffractive photoproduction to observe a unique spin interference
pattern in the angular distribution of decays.
The observed interference is a result of an overlap of two wave functions at a
distance an order of magnitude larger than the travel distance
within its lifetime. The strong-interaction nuclear radii were extracted from
these diffractive interactions, and found to be fm () and fm (), larger than the nuclear charge
radii. The observable is demonstrated to be sensitive to the nuclear geometry
and quantum interference of non-identical particles
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