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Register a new userBeam-energy dependence of charge separation along the magnetic field in Au+Au collisions at RHIC
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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.
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We report the energy dependence of mid-rapidity (anti-)deuteron production in Au+Au collisions at $sqrt{s_text{NN}} = $7.7, 11.5, 14.5, 19.6, 27, 39, 62.4, and 200 GeV, measured by the STAR experiment at RHIC. The yield of deuterons is found to be well described by the thermal model. The collision energy, centrality, and transverse momentum dependence of the coalescence parameter $B_2$ are discussed. We find that the values of $B_2$ for anti-deuterons are systematically lower than those for deuterons, indicating that the correlation volume of anti-baryons is larger than that of baryons at $sqrt{s_text{NN}}$ from 19.6 to 39 GeV. In addition, values of $B_2$ are found to vary with collision energy and show a broad minimum around $sqrt{s_text{NN}}= $20 to 40 GeV, which might imply a change of the equation of state of the medium in these collisions.
We present results from a harmonic decomposition of two-particle azimuthal correlations measured with the STAR detector in Au+Au collisions for energies ranging from $sqrt{s_{NN}}=7.7$ GeV to 200 GeV. The third harmonic $v_3^2{2}=langle cos3(phi_1-phi_2)rangle$, where $phi_1-phi_2$ is the angular difference in azimuth, is studied as a function of the pseudorapidity difference between particle pairs $Deltaeta = eta_1-eta_2$. Non-zero {vthree} is directly related to the previously observed large-$Deltaeta$ narrow-$Deltaphi$ ridge correlations and has been shown in models to be sensitive to the existence of a low viscosity Quark Gluon Plasma (QGP) phase. For sufficiently central collisions, $v_3^2{2}$ persist down to an energy of 7.7 GeV suggesting that QGP may be created even in these low energy collisions. In peripheral collisions at these low energies however, $v_3^2{2}$ is consistent with zero. When scaled by pseudorapidity density of charged particle multiplicity per participating nucleon pair, $v_3^2{2}$ for central collisions shows a minimum near {snn}$=20$ GeV.
The two-particle angular correlation functions, $R_2$, of pions, kaons, and protons in Au+Au collisions at $sqrt{s_{NN}}=$ 7.7, 11.5, 14.5, 19.6, 27, 39, 62.4, and 200 GeV were measured by the STAR experiment at RHIC. These correlations were measured for both like-sign and unlike-sign charge combinations and versus the centrality. The correlations of pions and kaons show the expected near-side ({it i.e.}, at small relative angles) peak resulting from short-range mechanisms. The amplitudes of these short-range correlations decrease with increasing beam energy. However, the proton correlation functions exhibit strong anticorrelations in the near-side region. This behavior is observed for the first time in an A+A collision system. The observed anticorrelation is $p_{T}$-independent and decreases with increasing beam energy and centrality. The experimental results are also compared to the Monte Carlo models UrQMD, Hijing, and AMPT.
We present two-particle $p_{rm t}$ correlations as a function of event centrality for Au+Au collisions at $sqrt{s_{rm NN}}$ = 7.7, 11.5, 14.5, 19.6, 27, 39, 62.4, and 200 GeV at the Relativistic Heavy Ion Collider using the STAR detector. These results are compared to previous measurements from CERES at the Super Proton Synchrotron and from ALICE at the Large Hadron Collider. The data are compared with UrQMD model calculations and with a model based on a Boltzmann-Langevin approach incorporating effects from thermalization. The relative dynamical correlations for Au+Au collisions at $sqrt{s_{rm NN}}$ = 200 GeV show a power law dependence on the number of participant nucleons and agree with the results for Pb+Pb collisions at $sqrt{s_{rm NN}} = 2.76~ {rm TeV}$ from ALICE. As the collision energy is lowered from $sqrt{s_{rm NN}}$ = 200 GeV to 7.7 GeV, the centrality dependence of the relative dynamical correlations departs from the power law behavior observed at the higher collision energies. In central collisions, the relative dynamical correlations increase with collision energy up to $sqrt{s_{rm NN}}$ = 200 GeV in contrast to previous measurements that showed little dependence on the collision energy.
We present a measurement of the first-order azimuthal anisotropy, $v_1(y)$, of deuterons from Au+Au collisions at $sqrt{s_{NN}}$ = 7.7, 11.5, 14.5, 19.6, 27, and 39 GeV recorded with the STAR experiment at the Relativistic Heavy Ion Collider (RHIC). The energy dependence of the $v_1(y)$ slope, $dv_{1}/dy|_{y=0}$, for deuterons, where $y$ is the rapidity, is extracted for semi-central collisions (10-40% centrality) and compared to that of protons. While the $v_1(y)$ slopes of protons are generally negative for $sqrt{s_{NN}} >$ 10 GeV, those for deuterons are consistent with zero, a strong enhancement of the $v_1(y)$ slope of deuterons is seen at the lowest collision energy (the largest baryon density) at $sqrt{s_{NN}} =$ 7.7 GeV. In addition, we report the transverse momentum dependence of $v_1$ for protons and deuterons. The experimental results are compared with transport and coalescence models.
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