arXiv subjects

STAR Collaboration

Publications and source records attributed to STAR Collaboration.

At least 289 records · Page 16Linked to original sources

arXiv2004

Anisotropic flow at RHIC

We present the first measurement of directed flow ($v_1$) at the Relativistic Heavy Ion Collider (RHIC). $v_1$ is found to be consistent with zero at pseudorapidities $η$ from -1.2 to 1.2, then rises to the level of a couple of percent over the range $2.4 < |η| < 4$. The latter observation is similar to that from NA49 if the SPS rapidities are shifted by the difference in beam rapidity between RHIC and SPS. We studied the evolution of elliptic flow from p+p collisions through d+Au collision, and onto Au+Au collisions. Measurements of higher harmonics are presented and discussed.

nucl-ex↗

arXiv2004

Cross Sections and Transverse Single-Spin Asymmetries in Forward Neutral-Pion Production from Proton Collisions at \sqrt{s} = 200 GeV

Measurements of the production of forward high-energy pi0 mesons from transversely polarized proton collisions at \sqrt{s}=200 GeV are reported. The cross section is generally consistent with next-to-leading order perturbative QCD calculations. The analyzing power is small at x_F below about 0.3, and becomes positive and large at higher x_F, similar to the trend in data at \sqrt{s}<=20 GeV. The analyzing power is in qualitative agreement with perturbative QCD model expectations. This is the first significant spin result seen for particles produced with p_T>1 GeV/c at a polarized proton collider.

hep-ex↗

arXiv2004

Centrality and pseudorapidity dependence of charged hadron production at intermediate p_T in Au + Au collisions at sqrt(s_NN) = 130 GeV

We present STAR measurements of charged hadron production as a function of centrality in Au + Au collisions at sqrt(s_NN) = 130 GeV. The measurements cover a phase space region of 0.2 < p_T < 6.0 GeV/c in transverse momentum and -1 < eta < 1 in pseudorapidity. Inclusive transverse momentum distributions of charged hadrons in the pseudorapidity region 0.5 < |eta| < 1 are reported and compared to our previously published results for |eta| < 0.5. No significant difference is seen for inclusive p_T distributions of charged hadrons in these two pseudorapidity bins. We measured dN/deta distributions and truncated mean p_T in a region of p_T > p_T^cut, and studied the results in the framework of participant and binary scaling. No clear evidence is observed for participant scaling of charged hadron yield in the measured p_T region. The relative importance of hard scattering process is investigated through binary scaling fraction of particle production.

nucl-ex↗

arXiv2004

Azimuthal anisotropy and correlations in p+p, d+Au and Au+Au collisions at 200 GeV

We present the first measurement of directed flow ($v_1$) at RHIC. $v_1$ is found to be consistent with zero at pseudorapidities $η$ from -1.2 to 1.2, then rises to the level of a couple of percent over the range $2.4 < |η| < 4$. The latter observation is similar to data from NA49 if the SPS rapidities are shifted by the difference in beam rapidity between RHIC and SPS. Back-to-back jets emitted out-of-plane are found to be suppressed more if compared to those emitted in-plane, which is consistent with {\it jet quenching}. Using the scalar product method, we systematically compared azimuthal correlations from p+p, d+Au and Au+Au collisions. Flow and non-flow from these three different collision systems are discussed.

nucl-ex↗

arXiv2004

Three-Pion Hanbury-Brown-Twiss Correlations in Relativistic Heavy-Ion Collisions from the STAR Experiment

Data from the first physics run at the Relativistic Heavy-Ion Collider at Brookhaven National Laboratory, Au+Au collisions at $\sqrt{s_{NN}}=130$ GeV, have been analyzed by the STAR Collaboration using three-pion correlations with charged pions to study whether pions are emitted independently at freezeout. We have made a high-statistics measurement of the three-pion correlation function and calculated the normalized three-particle correlator to obtain a quantitative measurement of the degree of chaoticity of the pion source. It is found that the degree of chaoticity seems to increase with increasing particle multiplicity.

nucl-ex↗

arXiv2004

Particle-type dependence of azimuthal anisotropy and nuclear modification of particle production in Au+Au collisions at s(NN)**(1/2) = 200-GeV

We present STAR measurements of the azimuthal anisotropy parameter $v_2$ and the binary-collision scaled centrality ratio $R_{CP}$ for kaons and lambdas ($Λ+\barΛ$) at mid-rapidity in Au+Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV. In combination, the $v_2$ and $R_{CP}$ particle-type dependencies contradict expectations from partonic energy loss followed by standard fragmentation in vacuum. We establish $p_T \approx 5$ GeV/c as the value where the centrality dependent baryon enhancement ends. The $K_S^0$ and $Λ+\barΛ$ $v_2$ values are consistent with expectations of constituent-quark-number scaling from models of hadron fromation by parton coalescence or recombination.

nucl-ex↗

arXiv2004

Photon and neutral pion production in Au+Au collisions at sqrt(s_{NN}) = 130 GeV

We report the first inclusive photon measurements about mid-rapidity (|y|<0.5) from Au+Au collisions at sqrt(s_{NN}) = 130 GeV at RHIC. Photon pair conversions were reconstructed from electron and positron tracks measured with the Time Projection Chamber (TPC) of the STAR experiment. With this method, an energy resolution of Delta(E)/E = 2% at 0.5 GeV has been achieved. Reconstructed photons have also been used to measure the transverse momentum (pt) spectra of pi0 mesons about mid-rapidity (|y|<1) via the pi0 -> photon photon decay channel. The fractional contribution of the pi0 -> photon photon decay to the inclusive photon spectrum decreases by 20% +/- 5% between pt = 1.65 GeV/c and pt = 2.4 GeV/c in the most central events, indicating that relative to pi0 -> photon photon decay the contribution of other photon sources is substantially increasing.

nucl-ex↗

arXiv2003

Identified particle distributions in pp and Au+Au collisions at sqrt{s_NN}=200 GeV

Transverse mass and rapidity distributions for charged pions, charged kaons, protons and antiprotons are reported for sqrt{s_NN}=200 GeV pp and Au+Au collisions at RHIC. The transverse mass distributions are rapidity independent within |y|<0.5, consistent with a boost-invariant system in this rapidity interval. Spectral shapes and relative particle yields are similar in pp and peripheral Au+Au collisions and change smoothly to central Au+Au collisions. No centrality dependence was observed in the kaon and antiproton production rates relative to the pion production rate from medium-central to central collisions. Chemical and kinetic equilibrium model fits to our data reveal strong radial flow and relatively long duration from chemical to kinetic freeze-out in central Au+Au collisions. The chemical freeze-out temperature appears to be independent of initial conditions at RHIC energies.

nucl-ex↗

arXiv2003

Overview of results from the STAR experiment at RHIC

The Relativistic Heavy-Ion Collider (RHIC) provides Au+Au collisions at energies up to \sqrtsNN=200 GeV. STAR experiment was designed and constructed to investigate the behavior of strongly interacting matter at high energy density. An overview of some of the recent results from the STAR collaboration is given.

hep-ex↗

arXiv2003

Azimuthal anisotropy and correlations in the hard scattering regime at RHIC

Azimuthal anisotropy ($v_2$) and two-particle angular correlations of high $p_T$ charged hadrons have been measured in Au+Au collisions at $\sqrt{s_{NN}}$=130 GeV for transverse momenta up to 6 GeV/c, where hard processes are expected to contribute significantly. The two-particle angular correlations exhibit elliptic flow and a structure suggestive of fragmentation of high $p_T$ partons. The monotonic rise of $v_2(p_T)$ for $p_T<2$ GeV/c is consistent with collective hydrodynamical flow calculations. At $\pT>3$ GeV/c a saturation of $v_2$ is observed which persists up to $p_T=6$ GeV/c.

nucl-ex↗

arXiv2003

Narrowing of the Balance Function with Centrality in Au+Au Collisions at sqrt(sNN) = 130 GeV

The balance function is a new observable based on the principle that charge is locally conserved when particles are pair produced. Balance functions have been measured for charged particle pairs and identified charged pion pairs in Au+Au collisions at $\sqrt{s_{NN}}$ = 130 GeV at the Relativistic Heavy Ion Collider using STAR. Balance functions for peripheral collisions have widths consistent with model predictions based on a superposition of nucleon-nucleon scattering. Widths in central collisions are smaller, consistent with trends predicted by models incorporating late hadronization.

nucl-ex↗

arXiv2002

Interplay of correlations and fluctuations in Au+Au collisions at RHIC

Dynamic fluctuations in the local density of non-identified hadron tracks reconstructed in the STAR TPC are studied using the discrete wavelet transform power spectrum technique which involves mixed event reference sample comparison. The two-dimensional event-by-event analysis is performed in pseudo-rapidity (eta) and azimuthal angle (phi). HIJING simulations indicate that jets and mini-jets result in signals, visible without high pT selection, when the dynamic texture analysis is applied. Scanning a broad range of event multiplicities, we study the dependence of the signals on the initial conditions. Event structures are studied separately with positive and negative tracks, as well as both charges. A change of regime is observed in AuAu collisions at sqrt(S_NN}=130 GeV as event multiplicity is increased: a long range eta correlation (or suppressed fluctuation vis-a-vis mixed events) is seen in same charge data. This effect is qualitatively similar to one of the predicted manifestations of the Color Glass Condensate.

nucl-ex↗

arXiv2002

$K^{\star}(892)^{0}$ Production in Relativistic Heavy Ion Collisions at $\sqrt{s_{_{NN}}}=130$ GeV

We report the first observation of $K^{\star}(892)^{0}\toπK$ in relativistic heavy ion collisions. The transverse momentum spectrum of $(K^{\star0}+\bar{K}^{\star0})/2$ from central Au+Au collisions at $\sqrt{s_{_{NN}}}=130$ GeV is presented. The ratios of the $K^{\star0}$ yield derived from these data to the yields of negative hadrons, charged kaons, and $ϕ$ mesons have been measured in central and minimum bias collisions and compared with model predictions and comparable $e^{+}e^{-}$, $pp$, and $\bar{p}p$ results. The data indicate no dramatic reduction of $K^{\star0}$ production in relativistic heavy ion collisions despite expected losses due to rescattering effects.

nucl-ex↗

arXiv2002

Kaon Production and Kaon to Pion Ratio in Au+Au Collisions at $\snn=130$ GeV

Mid-rapidity transverse mass spectra and multiplicity densities of charged and neutral kaons are reported for Au+Au collisions at $\snn$=130 GeV at RHIC. The spectra are exponential in transverse mass, with an inverse slope of about 280 MeV in central collisions. The multiplicity densities for these particles scale with the negative hadron pseudo-rapidity density. The charged kaon to pion ratios are $K^+/π^- = 0.161 \pm 0.002 {\rm (stat)} \pm 0.024 {\rm (syst)}$ and $K^-/π^- = 0.146 \pm 0.002 {\rm (stat)} \pm 0.022 {\rm (syst)}$ for the most central collisions. The $K^+/π^-$ ratio is lower than the same ratio observed at the SPS while the $K^-/π^-$ is higher than the SPS result. Both ratios are enhanced by about 50% relative to p+p and $\bar{\rm p}$+p collision data at similar energies.

nucl-ex↗

arXiv2002

Mid-rapidity $Λ$ and $\barΛ$ Production in Au+Au Collisions at $\sqrt{s_{_{NN}}}=130$ GeV

We report the first measurement of strange ($Λ$) and anti-strange ($\barΛ$) baryon production from $\sqrt{s_{_{NN}}}=130$ GeV Au+Au collisions at the Relativistic Heavy Ion Collider (RHIC). Rapidity density and transverse mass distributions at mid-rapidity are presented as a function of centrality. The yield of $Λ$ and $\barΛ$ hyperons is found to be approximately proportional to the number of negative hadrons. The production of $\barΛ$ hyperons relative to negative hadrons increases very rapidly with transverse momentum. The magnitude of the increase cannot be described by existing hadronic string fragmentation models.

nucl-ex↗

arXiv2001

Measurement of inclusive antiprotons from Au+Au collisions at 130 GeV

We report the first measurement of inclusive antiproton production at mid-rapidity in Au+Au collisions at 130 GeV by the STAR experiment at RHIC. The antiproton transverse mass distributions in the measured transverse momentum range of 0.25 < pT < 0.95 GeV/c are found to fall less steeply for more central collisions. The extrapolated antiproton rapidity density is found to scale approximately with the negative hadron multiplicity density.

nucl-ex↗

arXiv2001

Strangeness Production in Star at Rhic

Strangeness study is one of the major goal of the STAR experiment at RHIC. Results presented here have been obtained from analyses restricted to the mid-rapidity region of Au-Au collisions at $\sqrt{s_{NN}}$ = 130 GeV. An onset of the understanding of the quark matter behavior produced at this relativistic energy can be stressed from the investigation of the relative and absolute yields of strange particle production, their transverse mass distributions and from comparisons with previous results obtained by AGS and SPS experiments.

nucl-ex↗

arXiv2001

Flow and non-flow correlations from four-particle multiplets in STAR

Elliptic flow results are presented for Au + Au collisions at $\sqrt{s_{NN}} = 130$ GeV in RHIC. This signal is investigated as a function of transverse momentum, rapidity and centrality. Results from four-particle correlation analysis, which can filter out contributions to the flow signal from correlations unrelated to the event reaction plane (``non-flow''), are presented and compared to the conventional method, in which non-flow effects are treated as part of the systematic uncertainty.

hep-ex↗