We report systematic measurements of dielectron ($e^{\pm}e^{\pm}$)
invariant-mass $M_{ee}$ spectra at mid-rapidity in Au+Au collisions at
$\sqrt{s_{NN}}$ = 27, 39, and 62.4 GeV taken with the STAR ...detector at the
Relativistic Heavy Ion Collider. For all energies studied, a significant excess
yield of dielectrons is observed in the low-mass region (0.40$ < M_{ee} < 0.75$
MeV/$c^2$) compared to hadronic cocktail simulations at freeze-out. Models that
include an in-medium broadening of the $\rho$-meson spectral function
consistently describe the observed excess. In addition, we report
acceptance-corrected dielectron-excess spectra for Au+Au collisions at
mid-rapidity ($\left|y_{ee}\right|$ $<$ 1) in the 0$-$80% centrality bin for
each collision energy. The integrated excess yields for $0.4 < M_{ee} < 0.75\
\textrm{GeV}/c^{2}$, normalized by the charged particle multiplicity at
mid-rapidity, are compared with previously published measurements for Au+Au at
$\sqrt{s_{NN}}$ = 19.6 and 200 GeV. The normalized excess yields in the
low-mass region show no significant collision energy dependence. The data,
however, are consistent with model calculations that demonstrate a modest
energy dependence.
We present measurements of three-particle correlations for various harmonics in Au+Au collisions at energies ranging from \(\sqrt{s_{{\rm NN}}}=7.7\) to 200 GeV using the STAR detector. The quantity ...\(\langle\cos(m\phi_1+n\phi_2-(m+n)\phi_3)\rangle\) is evaluated as a function of \(\sqrt{s_{{\rm NN}}}\), collision centrality, transverse momentum, \(p_T\), pseudo-rapidity difference, \(\Delta\eta\), and harmonics (\(m\) and \(n\)). These data provide detailed information on global event properties like the three-dimensional structure of the initial overlap region, the expansion dynamics of the matter produced in the collisions, and the transport properties of the medium. A strong dependence on \(\Delta\eta\) is observed for most harmonic combinations consistent with breaking of longitudinal boost invariance. Data reveal changes with energy in the two-particle correlation functions relative to the second-harmonic event-plane and provide ways to constrain models of heavy-ion collisions over a wide range of collision energies.
We present three-particle mixed-harmonic correlations \(\la \cos (m\phi_a + n\phi_b - (m+n) \phi_c)\ra\) for harmonics \(m,n=1-3\) for charged particles in \(\sqrt{s_{NN}}=\)200 GeV Au+Au collisions ...at RHIC. These measurements provide information on the three-dimensional structure of the initial collision zone and are important for constraining models of a subsequent low-viscosity quark-gluon plasma expansion phase. We investigate correlations between the first, second and third harmonics predicted as a consequence of fluctuations in the initial state. The dependence of the correlations on the pseudorapidity separation between particles show hints of a breaking of longitudinal invariance. We compare our results to a number of state-of-the art hydrodynamic calculations with different initial states and temperature dependent viscosities. These measurements provide important steps towards constraining the temperature dependent transport and the longitudinal structure of the initial state at RHIC.
In this erratum we report changes on the $D^0$ $p_T$ spectra and nuclear
modification factor ($R_{AA}$) in Au+Au collisions at
$\sqrt{s_{_{\mathrm{NN}}}$ = 200 GeV by fixing the errors in the ...efficiency
and selection criteria that affected the Au+Au results. The p+p reference
spectrum has changed as well and is updated with new fragmentation parameters.
Neutral beam injection into the Globus-M spherical tokamak at the early stage of discharge leads to the development of instabilities in a frequency range of 50–200 kHz, which have been identified as ...toroidal Alfvén eigenmodes (TAEs) 1. The influence of these modes on the confinement of fast particles has been studied with the aid of a neutral particle analyzer (NPA) and a neutron detector. The isotope effect was studied using hydrogen and deuterium both in the injected beam and in the target plasma. A correlation analysis of signals from magnetic probes showed that the observed modes in most cases contain a single harmonic with toroidal number
n
= 1. Upon the injection of deuterium into deuterium plasma, the development of TAEs led to a decrease in the neutron flux by 25%, whereas the fluxes of high-energy recharge atoms decreased by 75%. After the injection of hydrogen, a decrease in the flux measured by NPA did not exceed 25%.
Phys. Rev. Lett. 121, 132301 (2018) We report first measurements of $e^{+}e^{-}$ pair production in the mass
region 0.4 $<M_{ee}<$ 2.6 GeV/$c^{2}$ at low transverse momentum ($p_T<$ 0.15
GeV/$c$) in ...non-central Au$+$Au collisions at $\sqrt{s_{NN}}$ = 200 GeV and
U$+$U collisions at $\sqrt{s_{NN}}$ = 193 GeV. Significant enhancement factors,
expressed as ratios of data over known hadronic contributions, are observed in
the 40-80% centrality of these collisions. The excess yields peak distinctly at
low-$p_T$ with a width ($\sqrt{\langle p^2_T\rangle}$) between 40 to 60
MeV/$c$. The absolute cross section of the excess depends weakly on centrality
while those from a theoretical model calculation incorporating an in-medium
broadened $\rho$ spectral function and radiation from a Quark Gluon Plasma or
hadronic cocktail contributions increase dramatically with increasing number of
participant nucleons. Model calculations of photon-photon interactions
generated by the initial projectile and target nuclei describe the observed
excess yields but fail to reproduce the $p^{2}_{T}$ distributions.
Phys. Rev. D 98, 032013 (2018) The STAR Collaboration reports measurements of the longitudinal double-spin
asymmetry, $A_{LL}$, for neutral pions produced at forward directions in
polarized ...proton-proton collisions, at a center-of-mass energy of $510$ GeV.
Results are given for transverse momenta in the range $2<p_{T}<10$ GeV/$c$
within two regions of pseudorapidity that span $2.65<\eta<3.9$. These results
are sensitive to the polarized gluon parton distribution function, $\Delta
g(x)$, down to the region of Bjorken $x \sim 10^{-3}$. The asymmetries observed
are less than $\pm 5 \cdot 10^{-3}$ in magnitude, and will help constrain the
contribution to the spin of the proton from polarized gluons at low $x$, when
combined with other measurements as part of a global analysis.
Phys. Rev. D 98, 032011 (2018) We present the first measurements of the longitudinal double-spin asymmetry
$A_{LL}$ for dijets with at least one jet reconstructed within the
pseudorapidity range $0.8 ...< \eta < 1.8$. The dijets were measured in polarized
$pp$ collisions at a center-of-mass energy $\sqrt{s}$ = 200 GeV. Values for
$A_{LL}$ are determined for several distinct event topologies, defined by the
jet pseudorapidities, and span a range of parton momentum fraction $x$ down to
$x \sim$ 0.01. The measured asymmetries are found to be consistent with the
predictions of global analyses that incorporate the results of previous RHIC
measurements. They will provide new constraints on $\Delta g(x)$ in this poorly
constrained region when included in future global analyses.
Phys. Rev. D 98, 091103 (2018) The transverse spin transfer from polarized protons to $\Lambda$ and
$\bar{\Lambda}$ hyperons is expected to provide sensitivity to the transversity
distribution of the ...nucleon and to the transversely polarized fragmentation
functions. We report the first measurement of the transverse spin transfer to
$\Lambda$ and $\bar{\Lambda}$ along the polarization direction of the
fragmenting quark, $D_\mathrm{TT}$, in transversely polarized proton-proton
collisions at $\sqrt{s}=200\,\mathrm{GeV}$ with the STAR detector at RHIC. The
data correspond to an integrated luminosity of $18\,\mathrm{pb}^{-1}$ and cover
the pseudorapidity range $\left|\eta\right| < 1.2$ and transverse momenta
$p_{\mathrm{T}}$ up to $8\,\mathrm{GeV}/c$. The dependence on $p_\mathrm{T}$
and $\eta$ are presented. The $D_\mathrm{TT}$ results are found to be
comparable with a model prediction, and are also consistent with zero within
uncertainties.
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