423 research outputs found
Measurements of the Cross Section for e+e- -> hadrons at Center-of-Mass Energies from 2 to 5 GeV
We report values of for 85 center-of-mass energies between
2 and 5 GeV measured with the upgraded Beijing Spectrometer at the Beijing
Electron-Positron Collider.Comment: 5 pages, 3 figure
First Measurement of the Branching Fraction of the Decay psi(2S) --> tau tau
The branching fraction of the psi(2S) decay into tau pair has been measured
for the first time using the BES detector at the Beijing Electron-Positron
Collider. The result is ,
where the first error is statistical and the second is systematic. This value,
along with those for the branching fractions into e+e- and mu+mu of this
resonance, satisfy well the relation predicted by the sequential lepton
hypothesis. Combining all these values with the leptonic width of the resonance
the total width of the psi(2S) is determined to be keV.Comment: 9 pages, 2 figure
Significance of the Balance between Regulatory T (Treg) and T Helper 17 (Th17) Cells during Hepatitis B Virus Related Liver Fibrosis
<div><h3>Background</h3><p>Hepatitis B virus-related liver fibrosis (HBV-LF) always progresses from inflammation to fibrosis. However, the relationship between these two pathological conditions is not fully understood. Here, it is postulated that the balance between regulatory T (Treg) cells and T helper 17 (Th17) cells as an indicator of inflammation may predict fibrosis progression of HBV-LF.</p> <h3>Methodology/Principal Findings</h3><p>The frequencies and phenotypes of peripheral Treg and Th17 cells of seventy-seven HBeAg-positive chronic hepatitis B (CHB) patients who underwent liver biopsies and thirty healthy controls were determined by flow cytometry. In the periphery of CHB patients, both Treg and Th17 frequencies were significantly increased and correlated, and a lower Treg/Th17 ratio always indicated more liver injury and fibrosis progression. To investigate exact effects of Treg and Th17 cells during HBV-LF, a series of <em>in vitro</em> experiments were performed using purified CD4<sup>+</sup>, CD4<sup>+</sup>CD25<sup>+</sup>, or CD4<sup>+</sup>CD25<sup>−</sup> cells from the periphery, primary human hepatic stellate cells (HSCs) isolated from healthy liver specimens, human recombinant interleukin (IL)-17 cytokine, anti-IL-17 antibody and HBcAg. In response to HBcAg, CD4<sup>+</sup>CD25<sup>+</sup> cells significantly inhibited cell proliferation and cytokine production (especially IL-17 and IL-22) by CD4<sup>+</sup>CD25<sup>−</sup> cells in cell-contact and dose-dependent manners. In addition, CD4<sup>+</sup> cells from CHB patients, compared to those from HC subjects, dramatically promoted proliferation and activation of human HSCs. Moreover, in a dramatically dose-dependent manner, CD4<sup>+</sup>CD25<sup>+</sup> cells from CHB patients inhibited, whereas recombinant IL-17 response promoted the proliferation and activation of HSCs. Finally, <em>in vivo</em> evidence about effects of Treg/Th17 balance during liver fibrosis was obtained in concanavalin A-induced mouse fibrosis models via depletion of CD25<sup>+</sup> or IL-17<sup>+</sup> cells, and it’s observed that CD25 depletion promoted, whereas IL-17 depletion, alleviated liver injury and fibrosis progression.</p> <h3>Conclusions/Significance</h3><p>The Treg/Th17 balance might influence fibrosis progression in HBV-LF via increase of liver injury and promotion of HSCs activation.</p> </div
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
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
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
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
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