First results from STAR at RHIC

The Relativistic Heavy Ion Collider (RHIC) along with its complement of four experiments commenced operation for physics in the summer of 2000. Initial results on detector performance, preliminary physics results on hadron production, and the physics anticipated from the STAR experiment will be reported.     

Results from STAR experiment at RHIC

We present some of the important experimental results from nucleus-nucleus collision studies carried out by the STAR experiment at Relativistic Heavy Ion Collider (RHIC). The results suggests that central Au+Au collisions at RHIC has produced a dense and rapidly thermalizing matter with initial energy densities above the critical values predicted by lattice QCD for establishment of a quark-gluon plasma (QGP).     

Highlights from the STAR experiment at RHIC

Ultra-relativistic heavy-ion collisions produced at RHIC differ significantly from a superposition of proton-proton collisions. Evidence of collective expansion has been gathered. The yield of high transverse momentum particles has been found to be lower in head-on Au?Au collisions than is expected by scaling p-p collisions. Di-jet processes, which are frequent in p-p collisions, are almost absent in head-on Au?Au collisions. The current results from RHIC indicate that Au?Au collisions at $\sqrt {S_{NN} } = 130$ GeV and $\sqrt {S_{NN} } = 200$ GeV yield an expanding system that is opaque to high momentum partons.     

STAR results from the first year at RHIC

An overview of the latest results from the STAR experiment at RHIC is presented. Preliminary measurements of π,K,p,Λ and Ξ, plus their respective anti-particles atp _t < 2 GeV/c, where the majority of particle production occurs, allow us to probe the soft processes whilst the harder perturbative regime can be accessed by studying particle spectra and yields at higher momenta.     

First results from STAR EbyE analysis at RHIC

I review the first STAR event-by-event analysis of <p _p > fluctuations, event multiplicity fluctuations and large-scale two-particle p _t correlations. Significant nonstatistical charge-independent and charge-dependent fluctuations and correlations are observed.     

Charm production in the STAR experiment at RHIC

The single electron spectrum over a sufficiently broad range provides an indirect measurement of charm and beauty production at RHIC energies. Heavy-quarks are produced in parton-parton scattering in the initial phase of the collision and thus provide important information about the initial configuration of the colliding nuclei. Even more important, the final state spectra reflect the interactions of these heavy partons with the medium and thus allow us to probe the properties of the hot and dense system created in heavy-ion collisions. We present preliminary measurements of electron and positron spectra in pp and d + Au as well as preliminary elliptic flow measurements in Au + Au collisions at GeV performed by the STAR experiment. We describe the measurement techniques used to discriminate electrons from hadrons and compare the results with theoretical calculations. PACS. 25.75.-q Arrival of the final proofs: 20 June 2005     

Recent STAR Spin Results and Spin Measurements at RHIC

The STAR experiment provides measurements of single and double-spin asymmetries in longitudinally and transversely polarized p + p collisions at \(\sqrt s \) = 200 and 510 GeV to deepen our understanding on the proton spin structure and dynamics of parton interactions over a wide range of collision energy, momentum and rapidity of the various produced probes. Polarized processes with W^± production allow us to study the spin-flavor structure of the proton. Recent results obtained by STAR on the double longitudinal asymmetry, A_LL, of pion and jet production at \(\sqrt s \) = 200 and 510 GeV, the single longitudinal, A_L, and transverse, A_N, asymmetry of W^± production at \(\sqrt s \) = 510 GeV are overviewed. STAR results on azimuthal single transverse asymmetry of pion in p^↑ + (p, Au) and jet + π^± in p^↑ + p collisions are discussed. The proposed Forward Calorimeter System (FCS) and Forward Tracking System (FTS) upgrades at STAR would significantly improve the capabilities of existing detectors for measurements of observables such as asymmetries of pion, jet, Drell-Yan pairs produced at forward rapidities.     

Open charm production at RHIC: Recent results from STAR

We report recent measurements on the open charm production in d+Au and p+p collisions at $\sqrt {s_{NN} } = 200$ GeV from the STAR detector at RHIC. The two independent measurements — direct open charm hadron (D⁰, D^* etc.) reconstruction and non-photonic single electron spectrum — provide consistent results. The mid-rapidity charm differential cross section per nucleon-nucleon collision from d+Au collisions at RHIC is $d\sigma _{c\bar c}^{NN} /dy = 0.30 \pm 0.04(stat.) \pm 0.09(syst.)$ mb, which is higher than predictions from most of the NLO pQCD calculations. Implications for charmonium production in Au+Au collisions will also be discussed.     

Strangeness production at RHIC energies as seen by the STAR detector

In search for the Quark Gluon Plasma, which is one of the most exciting tasks of the Nuclear Physics these days, experimentalists reach for higher and higher energies in hope to establish most favourable conditions for its creation. A new generation of experiments for the RHIC accelerator is under construction and will be ready to take data in 1999. The focus for the STAR detector, located in the Wide Angle Hall of the RHIC accelerator, are hadronic observables. This paper will present STAR capabilities in the area of strangeness measurements and its ability to correlate them with other event characteristics.     

High-pt probes of the quark-gluon plasma: STAR/PHENIX results at RHIC

In this talk I review the use of scattered high-pt partons as probes of the quark-gluon plasma formed at RHIC. Recent results from both STAR and PHENIX are used to assess our current understanding of how these partons lose energy as they travel through the plasma and the extent that energy-loss can be used to extract properties of the plasma.     

Femtoscopy with multi-strange baryons at RHIC

An update on femtoscopic π-Ξ correlations in Au + Au collisions as measured by the STAR experiment at RHIC is presented. Centrality dependence of Gaussian radii and relative emission asymmetry was extracted for the first time.     

Anisotropic flow at RHIC

STAR’s measurement of directed flow for pions,kaons（K 0 S ）,protons and anti-protons,for Au＋Au collisions at 200 GeV obtained in Run7 are presented,as well as elliptic flow for identified particles measured in Au＋Au（Run7） and Cu＋Cu（Run5） collisions.It is found that the slope of proton v 1 （y） at midrapidity is extremely small.Elliptic flow results are compared to Hydro calculation and the discrepancy is discussed.     

Heavy-ion collisions at RHIC

The European Physical Journal C - In the first three years of running, the four RHIC experiments have collected a rich set of high quality data on nuclear collisions over a wide range in collision...     

z Scaling at RHIC

The concept of z scaling reflecting the general regularities of high-p _T particle production is reviewed. Properties of data z presentation are discussed. New data on high-p _T particle spectra obtained at the RHIC are analyzed in the framework of z presentation. It was shown that these experimental data confirm z scaling. Predictions of strange particle spectra are considered to be useful for understanding of strangeness origin in mesons and baryons and search for new physics phenomena at the RHIC. The text was submitted by the author in English.     

Hydrodynamic flow at RHIC

We review the apparently hydrodynamic behaviour of low transverse momentum particles (pT ≤ 1.5 GeV/c) produced in central and semicentral (b ≤ 7 fm) heavy ion collisions at RHIC. We investigate the impact parameter dependence of various observables, elaborating on radial and elliptic flow and particle multiplicities. We also discuss possible ambiguities in the initialization of the hydrodynamic system and present observables that should allow for their resolution.     

Collective dynamics at RHIC

We discuss the strong collective flow effects, 〈v ₂〉 and 〈β _t 〉, observed at RHIC (√ ^s NN=130 GeV). We argue that part of the collectivity could have already developed at partonic stage. To ‘see’ the partonic effects directly, measurements of multi-strange baryons like Ξ, Ω and charmed particles like J/ψ transverse momentum distributions are important. They provide one of the possible keys to the discovery of collective modes with the partonic (quarks and gluons) degrees of freedom.     

Finding charm at RHIC

Dileptons produced by hard scatterings, such as heavy quark decays and the Drell-Yan mechanism, probe the gluon and sea quark distributions in hadrons. In nucleus-nucleus collisions, these processes are the thermal ‘back-ground’. To determine the magnitude and behavior of this background, we calculate the hard scattering contribution to next to leading order in perturbative QCD at RHIC. We compare these results to optimistic estimates of thermal dilepton production and find that initial charm production is dominant. However, experimental cuts can reduce the charm background, enhancing thermal information.     

Entropy production at RHIC

For central heavy ion collisions at the RHIC energy, the entropy per unit rapidity dS/dy at freeze-out is extracted with minimal model dependence from available experimental measurements of particle yields, spectra, and source sizes estimated from two-particle interferometry. The extracted entropy rapidity density is consistent with lattice gauge theory results for a thermalized quark–gluon plasma with an energy density estimated from transverse energy production at RHIC.