Mid-rapidity open charm spectra from direct reconstruction of $D^{0}$($\bar{D^0}$)$\to K^{\mp}\pi^{\pm}$ in d+Au collisions and indirect electron/positron measurements via charm semileptonic decays in p+p and d+Au collisions at \srt = 200 GeV are reported. The $D^{0}$($\bar{D^0}$) spectrum covers a transverse momentum ($p_T$) range of 0.1 $<p_T<$ 3 \GeVc whereas the electron spectra cover a range of 1 $<p_T<$ 4 GeV/$c$. The electron spectra show approximate binary collision scaling between p+p and d+Au collisions. From these two independent analyses, the differential cross section per nucleon-nucleon binary interaction at mid-rapidity for open charm production from d+Au collisions at RHIC is $d\sigma^{NN}_{c\bar{c}}/dy$=0.30$\pm$0.04 (stat.)$\pm$0.09(syst.) mb. The results are compared to theoretical calculations. Implications for charmoniumm results in A+A collisions are discussed.
Inclusive electrons yield versus transverse momentum in D+AU collisions Data points at PT = 2.2, 2.7 and 3.5 GeV/c was obtained using only the TPC (Time Projection Chamber) and cover a pseudo-rapidity range of -1<eta<1, while other points were obtained using both a prototypeTime-of-Flight System and the TPC and cover a pseudo-rapidity range of -1<eta<0.
Inclusive electrons yield versus transverse momentum in P+P collisions.
D0 yield versus transverse momentum in D+AU collisions.
We present STAR measurements of the azimuthal anisotropy parameter $v_2$ and the binary-collision scaled centrality ratio $R_{CP}$ for kaons and lambdas ($\Lambda+\bar{\Lambda}$) 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 $\Lambda+\bar{\Lambda}$ $v_2$ values are consistent with expectations of constituent-quark-number scaling from models of hadron fromation by parton coalescence or recombination.
The minimum bias (0-80% of the collision cross-section) v2(pT) of K0s. Errors listed include statistical and point-to-point systematic uncertainties from the background. Additional non-flow systematic uncertainties are approximately -20%.
The minimum bias (0-80% of the collision cross-section) v2(pT) of Lambda+Lambdabar. Errors listed include statistical and point-to-point systematic uncertainties from the background. Additional non-flow systematic uncertainties are approximately -20%.
The minimum bias (0-80% of the collision cross-section) v2(pT) of charged hadrons. Errors listed include statistical and point-to-point systematic uncertainties from the background. Additional non-flow systematic uncertainties are approximately -20%.
We report high statistics measurements of inclusive charged hadron production in Au+Au and p+p collisions at \sqrtsNN=200 GeV. A large, approximately constant hadron suppression is observed in central Au+Au collisions for $5\lt\pT\lt12$ GeV/c. The collision energy dependence of the yields and the centrality and \pT dependence of the suppression provide stringent constraints on theoretical models of suppression. Models incorporating initial-state gluon saturation or partonic energy loss in dense matter are largely consistent with observations. We observe no evidence of \pT-dependent suppression, which may be expected from models incorporating jet attentuation in cold nuclear matter or scattering of fragmentation hadrons.
Inclusive invariant pT distributions of (h+ + h−)/2 for centrality-selected Au+Au and p+p NSD interactions. Hash marks at the top indicate bin boundaries for pT>4 GeV/c.The invariant cross section for p+p is indicated on the right vertical axis.
R200/130(pT ) vs. pT for (h+ + h−)/2 for four different centrality bins. The overall normalization uncertainty is +6−14% for the 40-60% bin and is negligible for the other panels. Calculations are described in the text.
RAA(pT) (Eq. 1) for (h+ + h−)/2 in |η|<0.5, for centrality-selected Au+Au spectra relative to the measured p+p spectrum. The p+p spectrum is common to all panels. Calculations are described in the text.
We present a systematic analysis of two-pion interferometry in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV using the STAR detector at RHIC. We extract the HBT radii and study their multiplicity, transverse momentum, and azimuthal angle dependence. The Gaussianess of the correlation function is studied. Estimates of the geometrical and dynamical structure of the freeze-out source are extracted by fits with blast wave parameterizations. The expansion of the source and its relation with the initial energy density distribution is studied.
1D correlation function for different values of SL (antisplitting cut).
1D correlation functions for differeny values of the maximum fraction of merged hits allowed.
Projections of the 3 dimensional correlation function and corresponding fits for negative pions from the 0-5% most central events and k_T = [150,250] MeV/c according to the standard and Bowler-Sinyukov procedures.
The results from the STAR Collaboration on directed flow (v_1), elliptic flow (v_2), and the fourth harmonic (v_4) in the anisotropic azimuthal distribution of particles from Au+Au collisions at sqrtsNN = 200 GeV are summarized and compared with results from other experiments and theoretical models. Results for identified particles are presented and fit with a Blast Wave model. Different anisotropic flow analysis methods are compared and nonflow effects are extracted from the data. For v_2, scaling with the number of constituent quarks and parton coalescence is discussed. For v_4, scaling with v_2^2 and quark coalescence is discussed.
Directed flow of charged hadrons v1{3} as a function of pseudorapidity for 10–70% centrality.
Directed flow of charged hadrons v1 {EP1,EP2} as a function of pseudorapidity for 20–60% centrality.
Charged hadron v2 for the centrality bins 5 to 10% and in steps of 10% starting at 10, 20, 30, 40, 50, 60, and 70 up to 80% along with min. bias as a function of p_T.
We report on the rapidity and centrality dependence of proton and anti-proton transverse mass distributions from Au+Au collisions at sqrt(sNN) = 130GeV as measured by the STAR experiment at RHIC. Our results are from the rapidity and transverse momentum range of |y|<0.5 and 0.35 <p_t<1.00GeV/c. For both protons and anti-protons, transverse mass distributions become more convex from peripheral to central collisions demonstrating characteristics of collective expansion. The measured rapidity distributions and the mean transverse momenta versus rapidity are flat within |y|<0.5. Comparisons of our data with results from model calculations indicate that in order to obtain a consistent picture of the proton(anti-proton) yields and transverse mass distributions the possibility of pre-hadronic collective expansion may have to be taken into account.
$p$ differential yield. Systematic uncertainties are $\pm$10%.
$\bar{p}$ differential yield. Systematic uncertainties are $\pm$10%.
Rapidity distribution of $p$. Combined statitiscal uncertainty and systematic uncertainty from PID contramination. Systematic uncertainties from the track reconstruction efficiency are $\pm$25%.
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.
Inclusive $\pi^{0}$ production cross section versus leading $\pi^{0}$ energy ($E_{\pi}$). The average transverse momentum ($\langle p_{T}\rangle$) is correlated with $E_{\pi}$, as the PFPD was at a fixed pseudorapidity ($\eta$). The inner error bars are statistical, and are smaller than the symbols for most points. The outer error bars combine these with the $E_{\pi}$-dependent systematic errors. The curves are NLO pQCD calculations evaluated at $\eta=3.8$ [29-31].
Analyzing powers versus Feynman $x$ ($x_{F}$). The average transverse momentum ($\langle p_{T}\rangle$) is correlated with $x_{F}$. The solid points are for identified $\pi^{0}$ mesons. The open points are for the total energy ($E_{\scriptsize{\mbox{tot}}}$), shifted by $x_{F}+0.01$. The inner error bars are statistical, and the outer combine these with the point-to-point systematic errors. The curves are from pQCD models evaluated at $p_{T}=1.5$ GeV/c [14-17]. The $A_{N}$ values are proportional to $A^{\scriptsize{\mbox{CNI}}}_{N}$, assumed to be 0.013 at 100 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 report measurements of transverse momentum $p_t$ spectra for ten event multiplicity classes of p-p collisions at $\sqrt{s} = 200$ GeV. By analyzing the multiplicity dependence we find that the spectrum shape can be decomposed into a part with amplitude proportional to multiplicity and described by a L\'evy distribution on transverse mass $m_t$, and a part with amplitude proportional to multiplicity squared and described by a gaussian distribution on transverse rapidity $y_t$. The functional forms of the two parts are nearly independent of event multiplicity. The two parts can be identified with the soft and hard components of a two-component model of p-p collisions. This analysis then provides the first isolation of the hard component of the $p_t$ spectrum as a distribution of simple form on $y_t$.
FIG. 1: Corrected and normalized charged-particle spectra on transverse momentum $p_t$ (left) and transverse rapidity $y_t$ (right) for 10 event multiplicity classes, displaced upward by successive factors 40 relative to $\hat{n}_{ch}$ = 1 at bottom. Solid curves represent reference function $n_s/n_{ch} · S_0(y_t)$ (cf.Sec. IV C). Dotted curves are spline fits to guide the eye.
FIG. 1: Corrected and normalized charged-particle spectra on transverse momentum $p_t$ (left) and transverse rapidity $y_t$ (right) for 10 event multiplicity classes, displaced upward by successive factors 40 relative to $\hat{n}_{ch}$ = 1 at bottom. Solid curves represent reference function $n_s/n_{ch} · S_0(y_t)$ (cf.Sec. IV C). Dotted curves are spline fits to guide the eye.
FIG. 2. Left: Relative residuals from power-law fits to $p_{t}$ spectra in Fig. 1. The hatched band represents the expected statistical errors for STAR data. Right: Exponents $n$ from power-law fits to data (solid points) and to corresponding twocomponent fixed-model functions (open circles, see Sec. VI) compared to the two-component fixed-model Lévy exponent $12.8 \pm 0.15$ (hatched band). NOTE 1: For points with invisible error bars, the point size was considered as an absolute upper limit for the uncertainty. NOTE 2: The "data_stat" uncertainty corresponds to the expected statistical error (hatched band).
We present first measurements of the pseudorapidity and azimuth $(\eta,\phi)$ bin-size dependence of event-wise mean transverse momentum $<p_{t} >$ fluctuations for Au-Au collisions at $\sqrt{s_{NN}} = 200$ GeV. We invert that dependence to obtain $p_t$ autocorrelations on differences $(\eta_\Delta,\phi_\Delta)$ interpreted to represent velocity/temperature distributions on ($\eta,\phi$). The general form of the autocorrelations suggests that the basic correlation mechanism is parton fragmentation. The autocorrelations vary strongly with collision centrality, which suggests that fragmentation is strongly modified by a dissipative medium in the more central
Correlation amplitudes $B_{1}, B_{2}, B_{3}$ as well as positive-peak widths for pseudorapidity ($\sigma_{\eta_{1}}$) and azimuth ($\sigma_{\phi_{1}}$), plotted on mean participant path length $\nu$.
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