40 research outputs found
Low Energy Light Yield of Fast Plastic Scintillators
Compact neutron imagers using double-scatter kinematic reconstruction are
being designed for localization and characterization of special nuclear
material. These neutron imaging systems rely on scintillators with a rapid
prompt temporal response as the detection medium. As n-p elastic scattering is
the primary mechanism for light generation by fast neutron interactions in
organic scintillators, proton light yield data are needed for accurate
assessment of scintillator performance. The proton light yield of a series of
commercial fast plastic organic scintillators---EJ-200, EJ-204, and
EJ-208---was measured via a double time-of-flight technique at the 88-Inch
Cyclotron at Lawrence Berkeley National Laboratory. Using a tunable deuteron
breakup neutron source, target scintillators housed in a dual photomultiplier
tube configuration, and an array of pulse-shape-discriminating observation
scintillators, the fast plastic scintillator light yield was measured over a
broad and continuous energy range down to proton recoil energies of
approximately 50 keV. This work provides key input to event reconstruction
algorithms required for utilization of these materials in emerging neutron
imaging modalities.Comment: 15 pages, 6 figure
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 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
Regulated ATF5 loss-of-function in adult mice blocks formation and causes regression/eradication of gliomas
Glioblastomas are among the most incurable cancers. Our past findings indicated that glioblastoma cells, but not neurons or glia, require the transcription factor ATF5 (activating transcription factor 5) for survival. However, it was unknown whether interference with ATF5 function can prevent or promote regression/eradication of malignant gliomas in vivo. To address this issue, we created a mouse model by crossing a human glial fibrillary acidic protein (GFAP) promoter-tetracycline transactivator mouse line with tetracycline operon-dominant negative-ATF5 (d/n-ATF5) mice to establish bi-transgenic mice. In this model, d/n-ATF5 expression is controlled by doxycycline and the promoter for GFAP, a marker for stem/progenitor cells as well as gliomas. Endogenous gliomas were produced with high efficiency by retroviral delivery of platelet-derived growth factor (PDGF)-B and p53-short hairpin RNA (shRNA) in adult bi-transgenic mice in which expression of d/n-ATF5 was spatially and temporally regulated. Induction of d/n-ATF5 before delivery of PDGF-B/p53-shRNA virus greatly reduced the proportion of mice that formed tumors. Moreover, d/n-ATF5 induction after tumor formation led to regression/eradication of detectable gliomas without evident damage to normal brain cells in all 24 mice assessed
Observation of the electromagnetic field effect via charge-dependent directed flow in heavy-ion collisions at the Relativistic Heavy Ion Collider
The deconfined quark-gluon plasma (QGP) created in relativistic heavy-ion
collisions enables the exploration of the fundamental properties of matter
under extreme conditions. Non-central collisions can produce strong magnetic
fields on the order of Gauss, which offers a probe into the
electrical conductivity of the QGP. In particular, quarks and anti-quarks carry
opposite charges and receive contrary electromagnetic forces that alter their
momenta. This phenomenon can be manifested in the collective motion of
final-state particles, specifically in the rapidity-odd directed flow, denoted
as . Here we present the charge-dependent measurements of
near midrapidities for , , and
in Au+Au and isobar (Ru+Ru and
Zr+Zr) collisions at 200 GeV, and
in Au+Au collisions at 27 GeV, recorded by the STAR detector at the
Relativistic Heavy Ion Collider. The combined dependence of the signal on
collision system, particle species, and collision centrality can be
qualitatively and semi-quantitatively understood as several effects on
constituent quarks. While the results in central events can be explained by the
and quarks transported from initial-state nuclei, those in peripheral
events reveal the impacts of the electromagnetic field on the QGP. Our data put
valuable constraints on the electrical conductivity of the QGP in theoretical
calculations
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 via charge-dependent azimuthal correlations relative to spectator and participant planes in Au+Au collisions at = 200 GeV
The chiral magnetic effect (CME) refers to charge separation along a strong
magnetic field due to imbalanced chirality of quarks in local parity and
charge-parity violating domains in quantum chromodynamics. The experimental
measurement of the charge separation is made difficult by the presence of a
major background from elliptic azimuthal anisotropy. This background and the
CME signal have different sensitivities to the spectator and participant
planes, and could thus be determined by measurements with respect to these
planes. We report such measurements in Au+Au collisions at a nucleon-nucleon
center-of-mass energy of 200 GeV at the Relativistic Heavy-Ion Collider. It is
found that the charge separation, with the flow background removed, is
consistent with zero in peripheral (large impact parameter) collisions. Some
indication of finite CME signals is seen with a significance of 1--3 standard
deviations in mid-central (intermediate impact parameter) collisions.
Significant residual background effects may, however, still be present.Comment: 8 pages, 3 figure