arXiv subjects

the STAR Collaboration

Publications and source records attributed to the STAR Collaboration.

13 recordsLinked to original sources

arXiv2012

Forward azimuthal correlations in 200 GeV p+p and d+Au collisions at STAR

Forward particle production and correlation measurements at RHIC can probe low-$x$ gluons. The suppression observed in back-to-back forward $π^{0}$+forward $π^{0}$ correlations at STAR in central d+Au collisions at STAR is consistent with a prediction of the Color Glass Condensate (CGC) calculation, indicating the gold nucleus probed at such low-$x$ is in a dense gluon state. The forward $π^{0}$ + near-forward jet-like cluster azimuthal correlations in 200 GeV p+p and d+Au collisions at STAR are studied, which are sensitive to the intermediate x region between forward+mid-rapidity correlations and forward+forward correlations. Together with the other measurements from STAR, which probe different regions of x, forward+near-forward di-hadron correlations can provide information to understand how sharp is the transition from dilute parton gas to dense gluon state.

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arXiv2012

Directed Flow of Identified Particles in Au + Au Collisions at $\sqrtsNN = 200$ GeV at RHIC

STAR's measurements of directed flow ($v_1$) around midrapidity for $π^{\pm}$, K$^{\pm}$, K$_S^0$, $p$ and $\bar{p}$ in Au + Au collisions at $\sqrtsNN = 200$ GeV are presented. A negative $v_1(y)$ slope is observed for most of produced particles ($π^{\pm}$, K$^{\pm}$, K$_{S}^{0}$ and $\bar{p}$). In 5-30% central collisions a sizable difference is present between the $v_1(y)$ slope of protons and antiprotons, with the former being consistent with zero within errors. The $v_1$ excitation function is presented. Comparisons to model calculations (RQMD, UrQMD, AMPT, QGSM with parton recombination, and a hydrodynamics model with a tilted source) are made. For those models which have calculations of $v_1$ for both pions and protons, none of them can describe $v_1(y)$ for pions and protons simultaneously. The hydrodynamics model with a tilted source as currently implemented cannot explain the centrality dependence of the difference between the $v_1(y)$ slopes of protons and antiprotons.

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arXiv2010

Dijet Cross Section and Longitudinal Double Spin Asymmetry Measurements in Polarized Proton-proton Collisions at \sqrt{s}=200 GeV at STAR

These proceedings show the preliminary results of the dijet cross sections and the dijet longitudinal double spin asymmetries A_LL in polarized proton-proton collisions at \sqrt{s} = 200 GeV at the mid-rapidity |eta| < 0.8. The integrated luminosity of 5.39 pb^{-1} collected during RHIC Run-6 was used in the measurements. The preliminary results are presented as functions of the dijet invariant mass M_jj. The dijet cross sections are in agreement with next-to-leading-order pQCD predictions. The A_LL is compared with theoretical predictions based on various parameterizations of polarized parton distributions of the proton. Projected precision of data analyzed to date from Run-9 are shown.

hep-ex↗

arXiv2009

Experimental study of local strong parity violation in relativistic nuclear collisions

Parity-odd domains, corresponding to non-trivial topological solutions of the QCD vacuum, might be created in relativistic heavy ions collisions. These domains are predicted to lead to charge separation along the system orbital momentum of the system created in non-central collisions. Three-particle mixed harmonics azimuthal correlator is a ¶even observable but directly sensitive to the charge separation effect. Using this observable to analyze Au+Au and Cu+Cu collisions at $\sqrt{s_{NN}}=200$ and 62 GeV, STAR detects a signal consistent with several of the theoretical expectations. Possible contributions from effects not related to parity violation are studied with existing event generators, which fail to describe the data. Future directions in studying the effect are discussed.

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arXiv2007

Mass, quark-number, and $\sqrt{s_{NN}}$ dependence of the second and fourth flow harmonics in ultra-relativistic nucleus-nucleus collisions

We present STAR measurements of the azimuthal anisotropy parameter $v_2$ for pions, kaons, protons, $Λ$, $\barΛ$, $Ξ+\barΞ$, and $Ω+ \barΩ$, along with $v_4$ for pions, kaons, protons, and $Λ+ \barΛ$ at mid-rapidity for Au+Au collisions at $\sqrt{s_{_{NN}}}=62.4$ and 200 GeV. The $v_2(p_T)$ values for all hadron species at 62.4 GeV are similar to those observed in 130 and 200 GeV collisions. For observed kinematic ranges, $v_2$ values at 62.4, 130, and 200 GeV are as little as 10%--15% larger than those in Pb+Pb collisions at $\sqrt{s_{_{NN}}}=17.3$ GeV. At intermediate transverse momentum ($p_T$ from 1.5--5 GeV/c), the 62.4 GeV $v_2(p_T)$ and $v_4(p_T)$ values are consistent with the quark-number scaling first observed at 200 GeV. A four-particle cumulant analysis is used to assess the non-flow contributions to pions and protons and some indications are found for a smaller non-flow contribution to protons than pions. Baryon $v_2$ is larger than anti-baryon $v_2$ at 62.4 and 200 GeV perhaps indicating either that the initial spatial net-baryon distribution is anisotropic, that the mechanism leading to transport of baryon number from beam- to mid-rapidity enhances $v_2$, or that anti-baryon and baryon annihilation is larger in the in-plane direction.

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arXiv2005

Transverse-momentum dependent modification of dynamic texture in central Au+Au collisions at sqrt(S_NN)=200 GeV

Correlations in the hadron distributions produced in relativistic Au+Au collisions are studied in the discrete wavelet expansion method. The analysis is performed in the space of pseudorapidity (|eta| < 1) and azimuth (full 2 pi) in bins of transverse momentum (p_t) from 0.14 < p_t < 2.1 GeV/c. In peripheral Au+Au collisions a correlation structure ascribed to mini-jet fragmentation is observed. It evolves with collision centrality and p_t in a way not seen before which suggests strong dissipation of minijet fragmentation in the longitudinally-expanding medium.

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arXiv2004

Proton - Lambda correlations in Au-Au Collisions at $\sqrt{s_{NN}} = 200$ GeV from the STAR experiment

The space-time evolution of the source of particles formed in the collision of nuclei can be studied through particle correlations. The STAR experiment is dedicated to study ultra-relativistic heavy ions collisions and allows to measure non-identical strange particle correlations. The source size can be extracted by studying $p-Λ$, $\bar{p}-\barΛ$, $\bar{p}-Λ$ and $p-\barΛ$ correlation functions. Strong interaction potential has been studied for these systems using an analytical model. Final State Interaction (FSI) parameters have been determined and has shown a significant annihilation process present in $\bar{p}-Λ$ and $p-\barΛ$ systems not present in $p-Λ$ and $\bar{p}-\barΛ$.

hep-ex↗

arXiv2002

Soft Particle Spectra at STAR

We presented the multiplicity and the spectra of many particles in Au+Au at sqrt(s_{_{NN}})=130 GeV measured by STAR detector. Their connections to initial condition, baryon creation, freeze-out condition and strangeness enhancement were discussed.

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arXiv2001

Resonance Studies at STAR

We report on the observed signals of ${K^{\star0}(892)}\toπK$ and $ϕ(1020)\to K^{+}K^{-}$ using the mixed-event method with powerful statistics from the large acceptance and highly efficient STAR TPC. Preliminary results from the first observation of such states from the year-one STAR data in $\sqrt{s_{NN}}=130$ GeV Au-Au collisions are presented. The $K^{\star0}/h^{-}$ ratios with an assumed $K^{\star0}$ $p_{T}$ inverse slope of 300MeV are compatible with that from pp at ISR. For 14% central Au+Au collisions, we observe $K^{\star0}/h^{-}=0.060\pm0.007(stat)$ and $\bar{K^{\star0}}/h^{-}=0.058\pm0.007(stat)$. We show that $\barΛ/Λ=0.77\pm0.07(stat)$ from this method is consistent with the measurement via decay topology.

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arXiv2001

Elliptic flow in Au+Au collisions at $\sqrt{s_{_{NN}}}$ = 130 GeV

We report the elliptic flow of charged and identified particles at mid-rapidity in Au+Au collisions at $\sqrt{s_{_{NN}}}=130$ GeV using the STAR TPC at RHIC. The integrated elliptic flow signal, $v_2$, for charged particles reaches values of about 0.06, indicating a higher degree of thermalization than at lower energies. The differential elliptic flow signal, $v_2$($p_t$) up to 1.5 GeV/$c$, shows a behavior expected from hydrodynamic model calculations. Above 1.5 GeV/$c$, the data deviate from the hydro predictions; however the $v_2$($p_t$) is still large, suggesting finite asymmetry for the products of hard scattering. For the identified particles, elliptic flow as a function of $p_t$ and centrality differ significantly for particles of different masses. This dependence can be accounted for in hydrodynamic models, indicating that the system created shows a behavior consistent with collective hydrodynamical flow.

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arXiv2000

Overview of the Status and Strangeness Capabilities of STAR

STAR is a large acceptance spectrometer capable of precision measurements of a wide variety of strange particles. We discuss the STAR detector, its configuration during the first two years of RHIC operation, and its initial performance for Au+Au collisions. The expected performance for strangeness physics and initial data on strange particle reconstruction in Au+Au collisions are presented.

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arXiv1999

High PT Physics with the STAR Experiment at RHIC

The STAR experiment at RHIC is a TPC-based, general purpose detector designed to obtain charged particle spectra, with an emphasis on hadrons over a large phase space. An electromagnetic calorimeter provides measurement of electrons, photons, pi-zeros and jets. Data-taking with Au+Au collisions at sqrt(s)= 200 GeV/c**2 begins in Fall 1999. The STAR experiment's investigation of techniques and signals using hard probes to study the high energy-density matter at RHIC and to search for quark-gluon plasma formation will be described.

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arXiv1998

Two-Photon Physics in Nucleus-Nucleus Collisions at RHIC

Ultra-relativistic heavy-ions carry strong electromagnetic and nuclear fields. Interactions between these fields in peripheral nucleus-nucleus collisions can probe many interesting physics topics. This presentation will focus on coherent two-photon and photonuclear processes at RHIC. The rates for these interactions will be high. The coherent coupling of all the protons in the nucleus enhances the equivalent photon flux by a factor Z^2 up to an energy of ~3 GeV. The plans for studying coherent interactions with the STAR experiment will be discussed. Experimental techniques for separating signal from background will be presented.

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