We present $\Lambda\Lambda$ correlation measurements in heavy-ion collisions for Au+Au collisions at $\sqrt{s_{NN}}= 200$ GeV using the STAR experiment at the Relativistic Heavy-Ion Collider (RHIC). The Lednick\'{y}-Lyuboshitz analytical model has been used to fit the data to obtain a source size, a scattering length and an effective range. Implications of the measurement of the $\Lambda\Lambda$ correlation function and interaction parameters for di-hyperon searches are discussed.
The invariant mass distribution for $\Lambda$ and $\bar{\Lambda}$ produced in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV, for 0-80% centrality. The $\Lambda$ and $\bar{\Lambda}$ candidates lying in the mass range 1.112 to 1.120 GeV/c^2 were selected for the correlation measurement.
The $\Lambda\Lambda$ and $\bar{\Lambda}\bar{\Lambda}$ correlation function in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV, for 0-80% centrality.
The combined $\Lambda\Lambda$ and $\bar{\Lambda}\bar{\Lambda}$ correlation function for 0-80% centrality Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV.
We present measurements of elliptic flow ($v_2$) of electrons from the decays of heavy-flavor hadrons ($e_{HF}$) by the STAR experiment. For Au+Au collisions at $\sqrt{s_{\rm NN}} = $ 200 GeV we report $v_2$, for transverse momentum ($p_T$) between 0.2 and 7 GeV/c using three methods: the event plane method ($v_{2}${EP}), two-particle correlations ($v_2${2}), and four-particle correlations ($v_2${4}). For Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 62.4 and 39 GeV we report $v_2${2} for $p_T< 2$ GeV/c. $v_2${2} and $v_2${4} are non-zero at low and intermediate $p_T$ at 200 GeV, and $v_2${2} is consistent with zero at low $p_T$ at other energies. The $v_2${2} at the two lower beam energies is systematically lower than at $\sqrt{s_{\rm NN}} = $ 200 GeV for $p_T < 1$ GeV/c. This difference may suggest that charm quarks interact less strongly with the surrounding nuclear matter at those two lower energies compared to $\sqrt{s_{\rm NN}} = 200$ GeV.
Signal-to-background (S/B) ratio as a function of transverse momentum, Au+Au 200 GeV, 0-60% central events with minimum bias trigger
Signal-to-background (S/B) ratio as a function of transverse momentum, Au+Au 200 GeV, 0-60% central events with with High Tower (high pT) trigger
Signal-to-background (S/B) ratio as a function of transverse momentum, Au+Au 39 GeV, 0-60% central events with minimum bias trigger
We report a new high-precision measurement of the mid-rapidity inclusive jet longitudinal double-spin asymmetry, $A_{LL}$, in polarized $pp$ collisions at center-of-mass energy $\sqrt{s}=200$ GeV. The STAR data place stringent constraints on polarized parton distribution functions extracted at next-to-leading order from global analyses of inclusive deep inelastic scattering (DIS), semi-inclusive DIS, and RHIC $pp$ data. The measured asymmetries provide evidence for positive gluon polarization in the Bjorken-$x$ region $x>0.05$.
Jet neutral energy fraction (NEF) comparing data with simulations, where both are calculated with pT subtraction. This plot shows 8.4 < $p_T$ < 9.9 GeV/c.
Jet neutral energy fraction (NEF) comparing data with simulations, where both are calculated with pT subtraction. This plot shows 26.8 < $p_T$ < 31.6 GeV/c.
Inclusive jet $A_{LL}$ vs. parton jet $p_T$ for |eta|<0.5.
We report measurements of single- and double- spin asymmetries for $W^{\pm}$ and $Z/\gamma^*$ boson production in longitudinally polarized $p+p$ collisions at $\sqrt{s} = 510$ GeV by the STAR experiment at RHIC. The asymmetries for $W^{\pm}$ were measured as a function of the decay lepton pseudorapidity, which provides a theoretically clean probe of the proton's polarized quark distributions at the scale of the $W$ mass. The results are compared to theoretical predictions, constrained by recent polarized deep inelastic scattering measurements, and show a preference for a sizable, positive up antiquark polarization in the range $0.05
$E_T^e$ distribution of $W^{\pm}$ candidate events, background contributions, and sum of backgrounds and W -> ev MC signal. This plot is for Electron |eta|<0.5.
$E_T^e$ distribution of $W^{\pm}$ candidate events, background contributions, and sum of backgrounds and W -> ev MC signal. This plot is for Electron 0.5<|eta|<1.1.
$E_T^e$ distribution of $W^{\pm}$ candidate events, background contributions, and sum of backgrounds and W -> ev MC signal. This plot is for Positron |eta|<0.5.
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.
$D^0$ $p_{\rm T}$ differential invariant yield in p+p collisions (open circles), which has been updated with the latest global analysis of charm fragmentation ratios from Ref and also taking into account the $p_{\rm T}$ dependence of the fragmentation ratio between $D^0$ and $D^{*{\pm}}$ from PYTHIA 6.4. The systematic uncertainties are shown as square brackets.
Centrality dependence of the $D^0$ $p_{\rm T}$ differential invariant yield in Au+Au collisions (solid symbols). The curves are number-of-binary-collision-scaled Levy functions from fitting to the p+p result (open circles), which has been updated with the latest global analysis of charm fragmentation ratios from Ref and also taking into account the $p_{\rm T}$ dependence of the fragmentation ratio between $D^0$ and $D^{*{\pm}}$ from PYTHIA 6.4. The arrow denotes the upper limit with 90% confidence level of the last data point for 10$-$40% collisions. The systematic uncertainties are shown as square brackets.
Panels (ab), $D^0$ $R_{\rm AA}$ for peripheral 40$-$80% and semi a central 10$-$40% collisions; Panel (c), $D^0$ $R_{\rm AA}$ for 0$-$10% most central events (blue circles) compared with model calculations from the TAMU (solid curve), SUBATECH (dashed curve), Torino (dot-dashed curve), Duke (long-dashed and long-dot-dashed curves), and LANL groups (filled band). The open symbol indicates the result with the extrapolated p+p reference. The vertical lines and brackets around the data points denote the statistical and systematic uncertainties respectively. The vertical bars around unity denote the overall normalization uncertainties in the Au+Au and p+p data, respectively. The $R_{\rm AA}$ probability distribution for the 0$-$0.7 GeV/$c$ data point is largely skewed. The uncertainty we report is the 68.3% probability range with respect to the measured central value assuming Gaussian distribution.
Local parity-odd domains are theorized to form inside a Quark-Gluon-Plasma (QGP) which has been produced in high-energy heavy-ion collisions. The local parity-odd domains manifest themselves as charge separation along the magnetic field axis via the chiral magnetic effect (CME). The experimental observation of charge separation has previously been reported for heavy-ion collisions at the top RHIC energies. In this paper, we present the results of the beam-energy dependence of the charge correlations in Au+Au collisions at midrapidity for center-of-mass energies of 7.7, 11.5, 19.6, 27, 39 and 62.4 GeV from the STAR experiment. After background subtraction, the signal gradually reduces with decreased beam energy, and tends to vanish by 7.7 GeV. The implications of these results for the CME will be discussed.
The three-point correlator, $\gamma$, as a function of centrality for Au+Au collisions at 62.4 GeV.
The three-point correlator, $\gamma$, as a function of centrality for Au+Au collisions at 39 GeV.
The three-point correlator, $\gamma$, as a function of centrality for Au+Au collisions at 27 GeV.
STAR measurements of dihadron azimuthal correlations ($\Delta\phi$) are reported in mid-central (20-60\%) Au+Au collisions at $\sqrt{s_{_{\rm NN}}}=200$ GeV as a function of the trigger particle's azimuthal angle relative to the event plane, $\phi_{s}=|\phi_{t}-\psi_{\rm EP}|$. The elliptic ($v_2$), triangular ($v_3$), and quadratic ($v_4$) flow harmonic backgrounds are subtracted using the Zero Yield At Minimum (ZYAM) method. The results are compared to minimum-bias d+Au collisions. It is found that a finite near-side ($|\Delta\phi|<\pi/2$) long-range pseudorapidity correlation (ridge) is present in the in-plane direction ($\phi_{s}\sim 0$). The away-side ($|\Delta\phi|>\pi/2$) correlation shows a modification from d+Au data, varying with $\phi_{s}$. The modification may be a consequence of pathlength-dependent jet-quenching and may lead to a better understanding of high-density QCD.
raw correlation, Au+Au 200 GeV, 20-60%, 3<p_{T}^{(t)}<4 GeV/c, 1<p_{T}^{(a)}<2 GeV/c, |#eta|<1, slice 0.
raw correlation, Au+Au 200 GeV, 20-60%, 3<p_{T}^{(t)}<4 GeV/c, 1<p_{T}^{(a)}<2 GeV/c, |#eta|<1, slice 1.
raw correlation, Au+Au 200 GeV, 20-60%, 3<p_{T}^{(t)}<4 GeV/c, 1<p_{T}^{(a)}<2 GeV/c, |#eta|<1, slice 2.
We present results of analyses of two-pion interferometry in Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7, 11.5, 19.6, 27, 39, 62.4 and 200 GeV measured in the STAR detector as part of the RHIC Beam Energy Scan program. The extracted correlation lengths (HBT radii) are studied as a function of beam energy, azimuthal angle relative to the reaction plane, centrality, and transverse mass ($m_{T}$) of the particles. The azimuthal analysis allows extraction of the eccentricity of the entire fireball at kinetic freeze-out. The energy dependence of this observable is expected to be sensitive to changes in the equation of state. A new global fit method is studied as an alternate method to directly measure the parameters in the azimuthal analysis. The eccentricity shows a monotonic decrease with beam energy that is qualitatively consistent with the trend from all model predictions and quantitatively consistent with a hadronic transport model.
Angular oscillations of the HBT radii relative to the event plane from 20-30% central, 19.6 GeV Au+Au collisions for 0.15 < kT < 0.6 GeV/c. HHLW Radii uncorrected for resolution and binning for $R_{out}$.
Angular oscillations of the HBT radii relative to the event plane from 20-30% central, 19.6 GeV Au+Au collisions for 0.15 < kT < 0.6 GeV/c. HHLW Radii for resolution and binning for $R_{out}$, $R_{side}$, $R_{long}$, $R_{os}$, and $R_{ol}$ respectively.
Angular oscillations of the HBT radii relative to the event plane from 20-30% central, 19.6 GeV Au+Au collisions for 0.15 < kT < 0.6 GeV/c. Radius values according to global fit of Fourier Coefficients for $R_{out}$, $R_{side}$, $R_{long}$, $R_{os}$, and $R_{ol}$ respectively.
We report on the first measurement of the azimuthal anisotropy ($v_2$) of dielectrons ($e^{+}e^{-}$ pairs) at mid-rapidity from $\sqrt{s_{_{NN}}} = 200$ GeV Au+Au collisions with the STAR detector at RHIC, presented as a function of transverse momentum ($p_T$) for different invariant-mass regions. In the mass region $M_{ee}\!<1.1$ GeV/$c^2$ the dielectron $v_2$ measurements are found to be consistent with expectations from $\pi^{0}$, $\eta$, $\omega$ and $\phi$ decay contributions. In the mass region $1.1\!
The dielectron $v_2$ in the $\pi^0$ Dalitz decay region as a function of $p_T$ in different centralities from Au + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV.
Expected dielectron $v_2$ from $\pi^0$ Dalitz decay as a function of $p_T$ in different centralities from Au + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV.
The dielectron $v_2$ as a function of $p_T$ in minimum-bias Au + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV for the $\pi^0$ mass region.
We report the first measurements of the moments -- mean ($M$), variance ($\sigma^{2}$), skewness ($S$) and kurtosis ($\kappa$) -- of the net-charge multiplicity distributions at mid-rapidity in Au+Au collisions at seven energies, ranging from $\sqrt {{s_{\rm NN}}}$= 7.7 to 200 GeV, as a part of the Beam Energy Scan program at RHIC. The moments are related to the thermodynamic susceptibilities of net-charge, and are sensitive to the proximity of the QCD critical point. We compare the products of the moments, $\sigma^{2}/M$, $S\sigma$ and $\kappa\sigma^{2}$ with the expectations from Poisson and negative binomial distributions (NBD). The $S\sigma$ values deviate from Poisson and are close to NBD baseline, while the $\kappa\sigma^{2}$ values tend to lie between the two. Within the present uncertainties, our data do not show non-monotonic behavior as a function of collision energy. These measurements provide a distinct way of determining the freeze-out parameters in heavy-ion collisions by comparing with theoretical models.
The efficiency and centrality bin width corrected mean (M) of the net-charge multiplicity distributions as a function of number of participating nucleons $N_{part}$ for Au+Au collisions at 7.7 GeV. The dotted lines represent calculations from the central limit theorem. The error bars are statisticaland systematic errors.
The efficiency and centrality bin width corrected mean (M) of the net-charge multiplicity distributions as a function of number of participating nucleons $N_{part}$ for Au+Au collisions at 11.5 GeV. The dotted lines represent calculations from the central limit theorem. The error bars are statisticaland systematic errors.
The efficiency and centrality bin width corrected mean (M) of the net-charge multiplicity distributions as a function of number of participating nucleons $N_{part}$ for Au+Au collisions at 19.6 GeV. The dotted lines represent calculations from the central limit theorem. The error bars are statisticaland systematic errors.
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