Elliptic flow from nuclear collisions is a hadronic observable sensitive to the early stages of system evolution. We report first results on elliptic flow of charged particles at midrapidity in Au+Au collisions at sqrt(s_NN)=130 GeV using the STAR TPC at RHIC. The elliptic flow signal, v_2, averaged over transverse momentum, reaches values of about 6% for relatively peripheral collisions and decreases for the more central collisions. This can be interpreted as the observation of a higher degree of thermalization than at lower collision energies. Pseudorapidity and transverse momentum dependence of elliptic flow are also presented.
Elliptic flow as a function of centrality defined as nch/nmax. Also given is epsilon, the initial space eccentricity of the overlap region, as well as the cumulative fraction of events starting with the most central. From the results of the study of non-flow contributions by different subevent selections and the maximum magnitudes of the first and higher-order harmonics, we estimate a systematic error for v2 of about 0.007, with somewhat smaller uncertainty for the mid-centralities where the resolution of the event plane is high.
Elliptic flow as a function of transverse momen-tum for minimum bias events
We report results on the ratio of mid-rapidity anti-proton to proton yields in Au+Au collisions at $\rts = 130$ GeV per nucleon pair as measured by the STAR experiment at RHIC. Within the rapidity and transverse momentum range of $|y|<0.5$ and 0.4 $
pbar over p ratio vs. pt
pbar over p ratio vs. rapidity (y)
pbar over p ratio vs. centrality $(n_{ch}/n_{max})$
The minimum bias multiplicity distribution and the transverse momentum and pseudorapidity distributions for central collisions have been measured for negative hadrons (h-) in Au+Au interactions at sqrt(s_nn) = 130 GeV. The multiplicity density at midrapidity for the 5% most central interactions is dNh-/deta|_{eta = 0} = 280 +- 1(stat)+- 20(syst), an increase per participant of 38% relative to ppbar collisions at the same energy. The mean transverse momentum is 0.508 +- 0.012 GeV/c and is larger than in central Pb+Pb collisions at lower energies. The scaling of the h- yield per participant is a strong function of pt. The pseudorapidity distribution is almost constant within |eta|<1.
Normalized multiplicity distribution of $h^{−}$ with $p_{T} > 100$ MeV/$c$ at $|\eta| < 0.5$ in Au+Au collisions at $\sqrt{s_{NN}} = 130$ GeV. Systematic error on the vertical scale is estimated to be $10\%$. The systematic error on the horizontal scale is $6\%$ for the entire range of multiplicity. The shaded area is $5\%$ most central collisions, selected by ZDC coincidence. The solid curve is the prediction from the HIJING model.
$h^{−}$ $p_{T}$-spectra for the $5\%$ most central Au+Au collisions at midrapidity ($|\eta| < 0.1$) for several systems. The correlated systematical error is estimated to be below $6\%$. The curves are power-law fits to the data.
ratio of STAR and scaled UA1 $p_{T}$-distributions. The errors given are the errors of the STAR data only and do not include the systematic errors from the scaling of the UA1 data to $130$ GeV (i.e., the shaded region in Fig.2 lower panel). The STAR data is for the $5\%$ most central collisions.
We report first results on elliptic flow of identified particles at mid-rapidity in Au+Au collisions at $\sqrt{s_{_{NN}}}=130$ GeV using the STAR TPC at RHIC. The elliptic flow as a function of transverse momentum and centrality differs 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. The fit to the data with a simple model gives information on the temperature and flow velocities at freeze-out.
Differential elliptic flow for pions for minimum-bias events, the systematic uncertainty for minimum-bias data is 13%.
Differential elliptic flow for protons + antiprotons for minimum-bias events, the systematic uncertainty for minimum-bias data is 13%.
Differential elliptic flow for kaons for minimum-bias events, the systematic uncertainty for minimum-bias data is 13%.
Two-pion correlation functions in Au+Au collisions at $\sqrt{s_{NN}} = 130$ GeV have been measured by the STAR (Solenoidal Tracker at RHIC) detector. The source size extracted by fitting the correlations grows with event multiplicity and decreases with transverse momentum. Anomalously large sizes or emission durations, which have been suggested as signals of quark-gluon plasma formation and rehadronization, are not observed. The HBT parameters display a weak energy dependence over a broad range in $\sqrt{s_{NN}}$.
Multiplicity dependence of HBT parameters for low-pT (0.125-0.225 GeV/c) pi- pi- channel. They are Coulomb corrected (5 fm Gaussian source assumed), corrected for merging effects ("bad systematic" for STAR-HBT insiders), and corrected for finite-momentum-resolution effects. Systematic errors are estimated by the size of the merging correction and the effect of varying source size used in the Coulomb correction by +/- 1 fm.
Multiplicity dependence of HBT parameters for low-pT (0.125-0.225 GeV/c) pi+ pi+ channel. They are Coulomb corrected (5 fm Gaussian source assumed), corrected for merging effects ("bad systematic" for STAR-HBT insiders), and corrected for finite-momentum-resolution effects. Systematic errors are estimated by the size of the merging correction and the effect of varying source size used in the Coulomb correction by +/- 1 fm.
mT dependence of HBT parameters for high multiplicity (0-12%) collisions in pi- pi- channel. They are Coulomb corrected (5 fm Gaussian source assumed), corrected for merging effects ("bad systematic" for STAR-HBT insiders), and corrected for finite-momentum-resolution effects. Systematic errors are estimated by the size of the merging correction and the effect of varying source size used in the Coulomb correction by +/- 1 fm.
The first measurements of light antinucleus production in Au+Au collisions at RHIC are reported. The observed production rates for antideuterons and antihelions are much larger than in lower energy nucleus-nucleus collisions. A coalescence model analysis of the yields indicates that there is little or no increase in the antinucleon freeze-out volume compared to collisions at SPS energy. These analyses also indicate that the antihelion freeze-out volume is smaller than the antideuteron freeze-out volume.
Coalescence parameters $B_2$ and $B_3$ in Au+Au collisions at 130 GeV.
Invariant yields of $\overline{d}$ and $\overline{p}$. Systematic errors are estimated to be 15%.
Invariant yields of $^3\overline{\mathrm{He}}$ and $\overline{p}$. Systematic errors are estimated to be 15%.
We present the first measurement of midrapidity vector meson φ production in Au+Au collisions at RHIC (sNN=130 GeV) from the STAR detector. For the 11% highest multiplicity collisions, the slope parameter from an exponential fit to the transverse mass distribution is T=379±50(stat)±45(syst) MeV, the yield dN/dy=5.73±0.37(stat)±0.69(syst) per event, and the ratio Nφ/Nh− is found to be 0.021±0.001(stat)±0.004(syst). The measured ratio Nφ/Nh− and T for the φ meson at midrapidity do not change for the selected multiplicity bins.
Transverse mass distriution of $\phi$ for 0-11% centrality in Au+Au collisions at 130 GeV.
Transverse mass distriution of $\phi$ for 11-26% centrality in Au+Au collisions at 130 GeV.
Transverse mass distriution of $\phi$ for 26-85% centrality in Au+Au collisions at 130 GeV.
First measurements of charge-independent correlations on angular difference variables $\eta_1 - \eta_2$ (pseudorapidity) and $\phi_1 - \phi_2$ (azimuth) are presented for primary charged hadrons with transverse momentum $0.15 \leq p_t \leq 2$ GeV/$c$ and $|\eta| \leq 1.3$ from Au-Au collisions at $\sqrt{s_{NN}} = 130$ GeV. Strong charge-independent angular correlations are observed associated with jet-like structures and elliptic flow. The width of the jet-like peak on $\eta_1 - \eta_2$ increases by a factor 2.3 from peripheral to central collisions, suggesting strong coupling of semi-hard scattered partons to a longitudinally-expanding medium. New methods of jet analysis introduced here provide evidence for nonperturbative QCD medium effects in heavy ion collisions.
Two-particle CI joint autocorrelations $\widehat{N}(\widehat{r}-1)$ on $(\eta_{\Delta}, \phi_{\Delta})$ for most-central collisions.
Two-particle CI joint autocorrelations $\widehat{N}(\widehat{r}-1)$ on $(\eta_{\Delta}, \phi_{\Delta})$ for mid-central collisions.
Two-particle CI joint autocorrelations $\widehat{N}(\widehat{r}-1)$ on $(\eta_{\Delta}, \phi_{\Delta})$ for mid-peripheral collisions.
We have searched for strangelets in a triggered sample of 61 million central (top 4%) Au+Au collisions at $\sNN = 200 $GeV near beam rapidities at the STAR detector. We have sensitivity to metastable strangelets with lifetimes of order $\geq 0.1 ns$, in contrast to limits over ten times longer in AGS studies and longer still at the SPS. Upper limits of a few 10^{-6} to 10^{-7} per central Au+Au collision are set for strangelets with mass ${}^{>}_{\sim}30$ GeV/c^{2}.
Upper limit for neutral (Z=0) and charged (Z=5) strangelet as a function of mass.
Upper limit for charged (Z=1) strangelet as a function of lifetime.
We present the transverse momentum (pT) spectra for identified charged pions, protons and anti-protons from p+p and d+Au collisions at \sqrts_NN = 200 GeV. The spectra are measured around midrapidity (|y| < 0.5) over the range of 0.3 < pT < 10 GeV/c with particle identification from the ionization energy loss and its relativistic rise in the Time Projection Chamber and Time-of-Flight in STAR. The charged pion and proton+anti-proton spectra at high pT in p+p and d+Au collisions are in good agreement with a phenomenological model (EPOS) and with the next-to-leading order perturbative quantum chromodynamic (NLO pQCD) calculations with a specific fragmentation scheme and factorization scale. We found that all proton, anti-proton and charged pion spectra in p+p collisions follow xT-scalings for the momentum range where particle production is dominated by hard processes (pT > 2 GeV/c). The nuclear modification factor around midrapidity are found to be greater than unity for charged pions and to be even larger for protons at 2 < pT < 5 GeV/c.
Transverse momentum distribution for $\pi^+$ production in d+Au minbias events in the mid rapidity region, $|y|<0.5$.
Transverse momentum distribution for $\pi^+$ production in p+p NSD events in the mid rapidity region, $|y|<0.5$.
Transverse momentum distribution for $\pi^+$ production in d+Au collisions with centrality 0-20% in the mid rapidity region, $|y|<0.5$.
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