Elliptic flow holds much promise for studying the early-time thermalization attained in ultrarelativistic nuclear collisions. Flow measurements also provide a means of distinguishing between hydrodynamic models and calculations which approach the low density (dilute gas) limit. Among the effects that can complicate the interpretation of elliptic flow measurements are azimuthal correlations that are unrelated to the reaction plane (non-flow correlations). Using data for Au + Au collisions at sqrt{s_{NN}} = 130 GeV from the STAR TPC, it is found that four-particle correlation analyses can reliably separate flow and non-flow correlation signals. The latter account for on average about 15% of the observed second-harmonic azimuthal correlation, with the largest relative contribution for the most peripheral and the most central collisions. The results are also corrected for the effect of flow variations within centrality bins. This effect is negligible for all but the most central bin, where the correction to the elliptic flow is about a factor of two. A simple new method for two-particle flow analysis based on scalar products is described. An analysis based on the distribution of the magnitude of the flow vector is also described.
Correlation between the event plane angles determined from pairs of subevents partitioned randomly (circles), partitioned with opposite signs of pseudorapidity (squares) and partitioned with opposite signs of charge (crosses). The correlation is plotted as a function of centrality, namely, charged particle multiplicity $n_{ch}$ divided by the maximum observed charged multiplicity, $n_{max}$.
The event plane resolution for full events as a function of centrality, using randomly partitioned subevents with (circles) and without (triangles) $p_{t}$ weight.
Elliptic flow signal $v_{2}$ as a function of centrality, from study of the correlation between particle pairs consisting of randomly chosen particles (circles), particles with opposite signs of charge (crosses), particles with the same signs of charge (triangles), and particles with opposite signs of pseudorapidity (squares).
Inclusive transverse momentum distributions of charged hadrons within 0.2<pT<6.0 GeV/c have been measured over a broad range of centrality for Au+Au collisions at sqrt(sNN)=130 GeV. Hadron yields are suppressed at high pT in central collisions relative to peripheral collisions and to a nucleon-nucleon reference scaled for collision geometry. Peripheral collisions are not suppressed relative to the nucleon-nucleon reference. The suppression varies continuously at intermediate centralities. The results indicate significant nuclear medium effects on high pT hadron production in heavy ion collisions at high energy.
Inclusive $p_T$ distributions of ($h^+ + h^−)/2$. Non-central bins are scaled down by the indicated factors. The combined statistical and systematic errors are shown. Curves are fits to Eq. (2). Hash marks at the top indicate bin boundaries for $p_T>1.5$ GeV/c.
Ratio of charged hadron yields within $|\eta| < 0.5$ for central over peripheral collisions, normalized to $\langle Nbin\rangle$.
$R_{AA}$($p_T$) for various centrality bins, for Au+Au relative to an NN reference spectrum. Error bars are described in the text. Errors between different $p_T$ and centrality bins are highly correlated.
The analyzing powers of π+ and π− were measured using an incident 22−GeV/c transversely polarized proton beam at the Brookhaven Alternating Gradient Synchrotron. A magnetic spectrometer measured π± inclusive asymmetries on a hydrogen and a carbon target. An elastic polarimeter with a CH2 target measured pp elastic-scattering asymmetries to determine the beam polarization using published data for the pp elastic analyzing power. Using the beam polarization determined from the elastic polarimeter and asymmetries from the inclusive spectrometer, analyzing powers AN for π± were determined in the xF and pT ranges (0.45–0.8) and (0.3–1.2 GeV/c), respectively. The analyzing power results are similar in both sign and character to other measurements at 200 and 11.7 GeV/c, confirming the expectation that high-energy pion inclusive analyzing powers remain large and relatively energy independent. This suggests that pion inclusive polarimetry may be a suitable method for measuring future beam polarizations at BNL RHIC or DESY HERA. Analyzing powers of π+ and π− produced on hydrogen and carbon targets are the same. Various models to explain inclusive analyzing powers are also discussed.
Analyzing power measurements for PI+ and PI- production on the carbon target at incident momentum 21.6 GeV. See text of article for definitions of method 'A' and 'B'.
Analyzing power measurements for inclusive PI- production from the hydrogen target.
Analyzing power measurements for inclusive PI+ production from the hydrogen target.
Diffractive photoproduction of vector mesons, gamma p --> V Y, where Y is a proton-dissociative system, has been measured in ep interactions with the ZEUS detector at HERA using an integrated luminosity of 25 pb^-1. The differential cross section, ds/dt, is presented for -t<12 GeV^2, where t is the square of the four-momentum transferred to the vector meson. The data span the range in photon-proton centre-of-mass energy, W, from 80 GeV to 120 GeV. The t distributions are well fit by a power law, ds/dt ~ (-t)^{-n}. The slope of the Pomeron trajectory, measured from the W dependence of the rho^0 and phi cross sections in bins of t, is consistent with zero. The ratios ds_(gamma p --> phi Y)/dt to ds_(gamma p --> rho^0 Y)/dt and ds_(gamma p --> J/psi Y)/dt to ds_(gamma p --> rho^0 Y)/dt increase with increasing -t. Decay-angle analyses for rho^0, phi and J/psi mesons have been carried out. For the rho^0 and phi mesons, contributions from single and double helicity flip are observed. The results are compared to expectations of theoretical models.
Differential cross section for RHO0 production. The second DSYS error is due to the modelling of the proton-dissociation process.
Differential cross section for PHI production. The second DSYS error is due to the modelling of the proton-dissociation process.
Differential cross section for J/PSI production. The second DSYS error is due to the modelling of the proton-dissociation process.
The production of neutrons carrying at least 20% of the proton beam energy ($\xl > 0.2$) in $e^+p$ collisions has been studied with the ZEUS detector at HERA for a wide range of $Q^2$, the photon virtuality, from photoproduction to deep inelastic scattering. The neutron-tagged cross section, $e p\to e' X n$, is measured relative to the inclusive cross section, $e p\to e' X$, thereby reducing the systematic uncertainties. For $\xl >$ 0.3, the rate of neutrons in photoproduction is about half of that measured in hadroproduction, which constitutes a clear breaking of factorisation. There is about a 20% rise in the neutron rate between photoproduction and deep inelastic scattering, which may be attributed to absorptive rescattering in the $\gamma p$ system. For $0.64 < \xl < 0.82$, the rate of neutrons is almost independent of the Bjorken scaling variable $x$ and $Q^2$. However, at lower and higher $\xl$ values, there is a clear but weak dependence on these variables, thus demonstrating the breaking of limiting fragmentation. The neutron-tagged structure function, ${{F}^{\rm\tiny LN(3)}_2}(x,Q^2,\xl)$, rises at low values of $x$ in a way similar to that of the inclusive \ff of the proton. The total $\gamma \pi$ cross section and the structure function of the pion, $F^{\pi}_2(x_\pi,Q^2)$ where $x_\pi = x/(1-\xl)$, have been determined using a one-pion-exchange model, up to uncertainties in the normalisation due to the poorly understood pion flux. At fixed $Q^2$, $F^{\pi}_2$ has approximately the same $x$ dependence as $F_2$ of the proton.
The XL bins, their acceptance and the acceptance uncertainty. The RH columnshows the contribution from the energy-scale uncertainty - this is completely c orrelated between the bins.
The slope of the PT**2 distribution from the 1995 DIS data. The uncertainties shown in this table were communicated to us by the authors, and supercede those given in the paper.
The normalized cross section (1/SIG)DSIG/dXL for leading neutrons with THETA < 0.8 mrad with statistical errors only.. For the lowest Q**2 data, the normalization uncertainty is +-5 PCT, and with XL > 0.52 there is a further normalization uncertainty of +-4 PCT.. For the intermediate Q**2 and DIS data the normalization uncertainty is +-4 PCT.
Cross sections for e-p charged current deep inelastic scattering have been measured at a centre-of-mass energy of 318 GeV with an integrated luminosity of 16.4 pb-1 using the ZEUS detector at HERA. Differential cross-sections d\sigma/dQ2, d\sigma/dx and d\sigma/dy are presented for Q2>200 GeV2. In addition, d2\sigma/dxdQ2 was measured in the kinematic range 280 GeV2 < Q2 < 30000 GeV2 and 0.015 < x < 0.42. The predictions of the Standard Model agree well with the measured cross sections. The mass of the W boson, determined from a fit to d\sigma/dQ2, is MW=80.3 \pm 2.1 (stat.) \pm 1.2 (syst.) \pm 1.0 (PDF) GeV.
The differential cross section DSIG/DQ**2.
The differential cross section DSIG/DX.
The differential cross section DSIG/DY.
We report the first observation of $K^{\star}(892)^{0}\to\pi K$ 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 $\phi$ 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.
Transverse mass spectrum of K*0 with YRAP = -0.5 to 0.5 for the 14 PCT most central interactions. Numerical values requested from the authors.
K*0 to negative hadron ratio using hadron data from Adler et al PRL 87,112303(2001).
K*0 to kaon ratio using STAR kaon data.
We report STAR results on the azimuthal anisotropy parameter v2 for strange particles K0S, L and Lbar at midrapidity in Au+Au collisions at sNN = 130 GeV at RHIC. The value of v2 as a function of transverse momentum of the produced particles pt and collision centrality is presented for both particles up to pt 3.0 GeV/c. A strong pt dependence in v2 is observed up to 2.0 GeV/c. The v2 measurement is compared with hydrodynamic model calculations. The physics implications of the pt integrated v2 magnitude as a function of particle mass are also discussed.
$v_2$ of $K_s^0$ as a function of $p_T$ for 0-11% centrality in Au+Au collisions at 130 GeV. Systematic errors of $\pm$0.005 for particle identification and background subtraction and $^{+0}_{-0.005}$ for nonflow effects.
$v_2$ of $K_s^0$ as a function of $p_T$ for 11-45% centrality in Au+Au collisions at 130 GeV. Systematic errors of $\pm$0.005 for particle identification and background subtraction and $^{+0}_{-0.005}$ for nonflow effects.
$v_2$ of $\Lambda+\bar{\Lambda}$ as a function of $p_T$ for 0-11% centrality in Au+Au collisions at 130 GeV. Systematic errors of $\pm$0.005 for particle identification and background subtraction and $^{+0}_{-0.005}$ for nonflow effects.
We have measured the production of strange baryons and antibaryons in 340-GeV/c Σ−+C and 260-GeV/c n+C interactions. The single xF distributions show the expected leading particle effect, and the single pt2 distributions show a distinct nonthermal behavior. The xF distributions of Λ-Λ pairs indicate two different phase space distributions for the two coincident baryons. On the other hand two Λ¯’s show identical distributions. Momentum conservation during the formation process may represent a significant source for the observed behavior.
Total inclusive LAMBDA and LAMBDABAR production cross sections for the SIGMA- beam on the Carbon target.
Total inclusive LAMBDA and LAMBDABAR production cross sections for the Neutron beam on the Carbon target.
Total inclusive LAMBDA LAMBDA and LAMBDABAR LAMBDABAR pair production crosssections for the SIGMA- beam on the Carbon target.
Diffractive dissociation of virtual photons, gamma* p-->Xp, has been studied in ep interactions with the ZEUS detector at HERA using an integrated luminosity of approx. 10 pb^-1. The data cover photon virtualities 0.17 < Q^2< 0.70 GeV^2 and 3 < Q^2< 80 GeV^2 with 3<M_X<38 GeV, where M_X is the mass of the hadronic final state.
The double differential cross section d2sig/dmx/dt measured with the LPS method for the Q**2 range 0.17 to 0.70 GeV**2.
The double differential cross section d2sig/dmx/dt measured with the LPS method for the Q**2 range 3 to 9 GeV**2.
The double differential cross section d2sig/dmx/dt measured with the LPS method for the Q**2 range 9 to 80 GeV**2.
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