86 research outputs found
ATHENA detector proposal - a totally hermetic electron nucleus apparatus proposed for IP6 at the Electron-Ion Collider
ATHENA has been designed as a general purpose detector capable of delivering the full scientific scope of the Electron-Ion Collider. Careful technology choices provide fine tracking and momentum resolution, high performance electromagnetic and hadronic calorimetry, hadron identification over a wide kinematic range, and near-complete hermeticity.This article describes the detector design and its expected performance in the most relevant physics channels. It includes an evaluation of detector technology choices, the technical challenges to realizing the detector and the R&D required to meet those challenges
Pair invariant mass to isolate background in the search for the chiral magnetic effect in Au+Au collisions at = 200 GeV
Quark interactions with topological gluon configurations can induce local
chirality imbalance and parity violation in quantum chromodynamics, which can
lead to the chiral magnetic effect (CME) -- an electric charge separation along
the strong magnetic field in relativistic heavy-ion collisions. The
CME-sensitive azimuthal correlator observable () is contaminated
by background arising, in part, from resonance decays coupled with elliptic
anisotropy (). We report here the first differential measurements of the
correlator as a function of the pair invariant mass () in 20-50\%
centrality Au+Au collisions at = 200 GeV by the STAR
experiment at RHIC. Strong resonance background contributions to
are observed. At large where this background is significantly
reduced, the value is found to be also significantly smaller. An
event shape engineering technique is deployed to determine the
background shape as a function of . A -independent signal,
possibly indicating a -integrated CME contribution, is extracted
to be = (0.03 0.06 0.08)
, or of the inclusive GeV/). This presents an
upper limit of , or of the inclusive result at
confidence level.Comment: 7 pages, 4 figure
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
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