Suppression of Upsilon production in d plus Au and Au plus Au collisions at root S-NN=200 GeV

We report measurements of Upsilon meson production in p + p, d + Au, and Au + Au collisions using the STAR detector at RHIC. We compare the Upsilon yield to the measured cross section in p + p collisions in order to quantify any modifications of the yield in cold nuclear matter using d + Au data and in hot nuclear matter using Au + Au data separated into three centrality classes. Our p + p measurement is based on three times the statistics of our previous result. We obtain a nuclear modification factor for Upsilon (1S + 2S + 3S) in the rapidity range vertical bar y vertical bar < 1 in d + Au collisions of R-dAu = 0.79 +/- 0.24(stat.) +/- 0.03(syst.) +/- 0.10(p + p syst.). A comparison with models including shadowing and initial state parton energy loss indicates the presence of additional cold-nuclear matter suppression. Similarly, in the top 10% most-central Au + Au collisions, we measure a nuclear modification factor of R-AA = 0.49 +/- 0.1(stat.) +/- 0.02(syst.) +/- 0.06(p + p syst.), which is a larger suppression factor than that seen in cold nuclear matter. Our results are consistent with complete suppression of excited-state Upsilon mesons in Au + Au collisions. The additional suppression in Au + Au is consistent with the level expected in model calculations that include the presence of a hot, deconfined Quark-Gluon Plasma. However, understanding the suppression seen in d + Au is still needed before any definitive statements about the nature of the suppression in Au + Au can be made735127137CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPRHIC Operations Group; NERSC Center at LBNL; KISTI Center in Korea; Open Science Grid consortium; National Science Foundation (NSF); Centre National de la Recherche Scientifique (CNRS); Ministry of Education and Science, Russian Federation; National Natural Science Foundation of China (NSFC); Chinese Academy of Sciences; Korean Research Foundation, GA; Ministry of Education, Youth & Sports - Czech Republic; FIAS of Germany; Department of Atomic Energy (DAE); Department of Science & Technology (India); Council of Scientific & Industrial Research (CSIR) - India; National Science Center, Poland; RosAtom of Russia ; RCF at BNL; United States Department of Energy (DOE); United States Department of Energy (DOE); Ministry of Education, China; Ministry of Science and Technology, China; Ministry of Science, Education and Sports, Republic of Croatia; National Science Foundation (NSF); NSF - Directorate for Mathematical & Physical Sciences (MPS

Beam-Energy Dependence of the Directed Flow of Protons, Antiprotons, and Pions in Au plus Au Collisions

Rapidity-odd directed flow (upsilon 1) measurements for charged pions, protons, and antiprotons near midrapidity (y = 0) are reported in root(S)(NN) = 7.7, 11.5, 19.6, 27, 39, 62.4, and 200 GeVAu+Au collisions as recorded by the STAR detector at the Relativistic Heavy Ion Collider. At intermediate impact parameters, the proton and net-proton slope parameter d upsilon(1) = d upsilon(1)vertical bar (y=0) shows a minimum between 11.5 and 19.6 GeV. In addition, the net-proton d upsilon(1) = d upsilon(1)vertical bar (y=0) changes sign twice between 7.7 and 39 GeV. The proton and net-proton results qualitatively resemble predictions of a hydrodynamic model with a first-order phase transition from hadronic matter to deconfined matter, and differ from hadronic transport calculations

Beam Energy Dependence of Moments of the Net-Charge Multiplicity Distributions in Au plus Au Collisions at RHIC

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 midrapidity in Au + Au collisions at seven energies, ranging from root s(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 location 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 (NBDs). The S sigma values deviate from the Poisson baseline and are close to the NBD baseline, while the kappa sigma(2) values tend to lie between the two. Within the present uncertainties, our data do not show nonmonotonic behavior as a function of collision energy. These measurements provide a valuable tool to extract the freeze-out parameters in heavy-ion collisions by comparing with theoretical models

Dielectron Mass Spectra from Au plus Au Collisions at root s(NN)=200 Ge V

We report the STAR measurements of dielectron (e(+)e(-)) production at midrapidity (vertical bar y(ee)vertical bar < 1) in Au + Au collisions at root s(NN) = 200 GeV. The measurements are evaluated in different invariant mass regions with a focus on 0.30-0.76 (rho-like), 0.76-0.80 (omega-like), and 0.98-1.05 (phi-like) GeV/c(2). The spectrum in the omega-like and phi-like regions can be well described by the hadronic cocktail simulation. In the rho-like region, however, the vacuum rho spectral function cannot describe the shape of the dielectron excess. In this range, an enhancement of 1.77 +/- 0.11(stat) +/- 0.24(syst) +/- 0.33(cocktail) is determined with respect to the hadronic cocktail simulation that excludes the rho meson. The excess yield in the rho-like region increases with the number of collision participants faster than the omega and phi yields. Theoretical models with broadened rho contributions through interactions with constituents in the hot QCD medium provide a consistent description of the dilepton mass spectra for the measurement presented here and the earlier data at the Super Proton Synchrotron energies

Beam-Energy Dependence of Charge Separation along the Magnetic Field in Au plus Au Collisions at RHIC

Local parity-odd domains are theorized to form inside a quark-gluon plasma 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. The experimental observation of charge separation has previously been reported for heavy-ion collisions at the top RHIC energies. In this Letter, 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. This implies the dominance of hadronic interactions over partonic ones at lower collision energies

Intermediate Point Norm Optimal Iterative Learning Control

A Norm-Optimal Iterative Learning Control (NOILC) solution is developed for the problem when tracking is only required at a subset of isolated time points along the trial duration. Well-defined convergence properties are presented, along with design guidelines and supporting experimental results using an electromechanical test facility

Centrality dependence of identified particle elliptic flow in relativistic heavy ion collisions at sNN=\sqrt{s_{NN}}= 7.7-62.4 GeV

Elliptic flow ($v_{2}$) values for identified particles at midrapidity in Au + Au collisions measured by the STAR experiment in the Beam Energy Scan at the Relativistic Heavy Ion Collider at $\sqrt{s_{NN}}=$ 7.7--62.4~GeV are presented for three centrality classes. The centrality dependence and the data at $\sqrt{s_{NN}}=$ 14.5~GeV are new. Except at the lowest beam energies we observe a similar relative $v_{2}$ baryon-meson splitting for all centrality classes which is in agreement within 15\% with the number-of-constituent quark scaling. The larger $v_{2}$ for most particles relative to antiparticles, already observed for minimum bias collisions, shows a clear centrality dependence, with the largest difference for the most central collisions. Also, the results are compared with A Multiphase Transport model and fit with a Blast Wave model

Jet-Hadron Correlations in root s(NN)=200 GeV p plus p and Central Au plus Au Collisions

Azimuthal angular correlations of charged hadrons with respect to the axis of a reconstructed (trigger) jet in Au + Au and p + p collisions at root s(NN) = 200 GeV in STAR are presented. The trigger jet population in Au + Au collisions is biased toward jets that have not interacted with the medium, allowing easier matching of jet energies between Au + Au and p + p collisions while enhancing medium effects on the recoil jet. The associated hadron yield of the recoil jet is significantly suppressed at high transverse momentum (p(T)(assoc)) and enhanced at low p(T)(assoc) in 0%-20% central Au + Au collisions compared to p + p collisions, which is indicative of medium-induced parton energy loss in ultrarelativistic heavy-ion collisions

Measurements of dielectron production in Au plus Au collisions at root s(NN)=200 GeV from the STAR experiment

We report on measurements of dielectron (e(+) e(-)) production in Au + Au collisions at a center-of-mass energy of 200 GeV per nucleon-nucleon pair using the STAR detector at BNL Relativistic Heavy Ion Collider. Systematic measurements of the dielectron yield as a function of transverse momentum (p(T)) and collision centrality show an enhancement compared to a cocktail simulation of hadronic sources in the low invariant-mass region (M-ee < 1 GeV / c(2)). This enhancement cannot be reproduced by the rho-meson vacuum spectral function. In minimum-bias collisions, in the invariant-mass range of 0.30-0.76 GeV / c(2), integrated over the full pT acceptance, the enhancement factor is 1.76 +/- 0.06 (stat.) +/- 0.26 (sys.) +/- 0.29 (cocktail). The enhancement factor exhibits weak centrality and pT dependence in STAR's accessible kinematic regions, while the excess yield in this invariant-mass region as a function of the number of participating nucleons follows a power-law shape with a power of 1.44 +/- 0.10. Models that assume an in-medium broadening of the rho-meson spectral function consistently describe the observed excess in these measurements. Additionally, we report on measurements of omega-and phi-meson production through their e+ e(-) decay channel. These measurements show good agreement with Tsallis blast-wave model predictions, as well as, in the case of the phi meson, results through its K+ K- decay channel. In the intermediate invariant-mass region (1.1 < Mee < 3 GeV / c(2)), we investigate the spectral shapes from different collision centralities. Physics implications for possible in-medium modification of charmed hadron production and other physics sources are discussed