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.
Measurements at 18 beam kinetic energies between 1975 and 2795 MeV and at 795 MeV are reported for the pp elastic scattering spin correlation parameter A00nn=(N,N;0,0)=CNN=ANN. The c.m. angular range is typically 60°-100°. These results are compared to previous data from Saturne II and other accelerators. A search for energy-dependent structure at fixed c.m. angles is performed. Comparisons are made to phase shift analysis and theoretical model predictions of this spin observable.
Measured values of CNN at EKIN 795 Mev.. Fractional systematic uncertainty in the absolute beam and target polarization is +-0.032.
Measured values of CNN at EKIN 1975 Mev.. Fractional systematic uncertainty in the absolute beam and target polarization is +-0.052.
Measured values of CNN at EKIN 2035 Mev (from run period III).. Fractional systematic uncertainty in the absolute beam and target polarization is +-0.051.
Dijet cross sections in neutral current deep inelastic ep scattering have been measured in the range $10 < \Q2 < 10^4$ GeV$^2$ with the ZEUS detector at HERA using an integrated luminosity of 38.4 pb$^{-1}$. The cross sections, measured in the Breit frame using the $\kt$ jet algorithm, are compared with next-to-leading-order perturbative QCD calculations using proton parton distribution functions. The uncertainties of the QCD calculations have been studied. The predictions are in reasonable agreement with the measured cross sections over the entire kinematic range.
Dijet cross section as a function of LOG10(Q**2).
Dijet cross section as a function of LOG10(MEAN(ET)**2/Q**2).
Dijet cross section as a function of LOG10(XI) for the ful Q**2 range.
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 report the first measurement of inclusive antiproton production at mid-rapidity in Au+Au collisions at 130 GeV by the STAR experiment at RHIC. The antiproton transverse mass distributions in the measured transverse momentum range of 0.25 < pT < 0.95 GeV/c are found to fall less steeply for more central collisions. The extrapolated antiproton rapidity density is found to scale approximately with the negative hadron multiplicity density.
Tranverse mass distributions for different centralities
Antiproton fit parameters and yields. Systematic errors are 10%.
Antiproton fit parameters and yields. Systematic errors are 10%.
The photon-proton total cross section has been measured in the process e+ p -> e+ gamma p -> e+ X with the ZEUS detector at HERA. Events were collected with photon virtuality Q^2 < 0.02 GeV^2 and average gamma-p center-of-mass energy W_{gamma p} = 209 GeV in a dedicated run, designed to control systematic effects, with an integrated luminosity of 49 nb^{-1}. The measured total cross section is sigma_{tot}^{gamma p} = 174 +- 1 (stat.) +- 13 (syst.) microbarns. The energy dependence of the cross section is compatible with parameterizations of high-energy p-p and p-pbar data.
Total GAMMA P cross section.
The dijet cross section in photoproduction has been measured with the ZEUS detector at HERA using an integrated luminosity of 38.6 pb$^{-1}$. The events were required to have a virtuality of the incoming photon, $Q^2$, of less than 1 GeV$^2$ and a photon-proton centre-of-mass energy in the range $134 < W_{\gamma p} < 277$ GeV. Each event contains at least two jets satisfying transverse-energy requirements of $E_{T}^{\rm jet1}>14$ GeV and $E_{T}^{\rm jet2}>11$ GeV and pseudorapidity requirements of $-1<\eta^{\rm jet1,2}<2.4$. The measurements are compared to next-to-leading-order QCD predictions. The data show particular sensitivity to the density of partons in the photon, allowing the validity of the current parameterisations to be tested.
Measured cross section as a function of COS(THETA*), where THETA* is the dijet angle in the parton-parton c.m. frame. The data are shown in two X(C=GAMMA) regions.
Measured cross section as a function of ET(JET1) for X(C=GAMMA) > 0.75 for:. -1 < ETARAP(JET1) < 0. -1 < ETARAP(JET2) < 0.
Measured cross section as a function of ET(JET1) for X(C=GAMMA) > 0.75 for:. 0 < ETARAP(JET1) < 1. -1 < ETARAP(JET2) < 0.
The exclusive photoproduction of J/psi mesons, gamma p->J/psi p, has been studied in ep collisions with the ZEUS detector at HERA, in the kinematic range 20<W<290 GeV, where W is the photon-proton centre-of-mass energy. The J/psi mesons were reconstructed in the muon and the electron decay channels using integrated luminosities of 38 pb^-1 and 55 pb^-1, respectively. The helicity structure of J/psi production shows that the hypothesis of s-channel helicity conservation is satisfied at the two standard-deviation level. The total cross section and the differential cross-section dsigma/dt, where t is the squared four-momentum transfer at the proton vertex, are presented as a function of W, for |t|<1.8 GeV^2. The t distribution exhibits an exponential shape with a slope parameter increasing logarithmically with W with a value b=4.15 \pm 0.05 (stat.)^{+0.30}_{-0.18} (syst.) GeV^-2 at W=90 GeV. The effective parameters of the Pomeron trajectory are alphapom(0) = 1.200 \pm 0.009(stat.)^{+0.004}_{-0.010}(syst.) and alphappom= 0.115 \pm 0.018(stat.)^{+0.008}_{-0.015}(syst.) GeV^-2.
The total exclusive J/PSI photoproduction cross section, the differential cross section extrapolated to t=0 and the slope parameter of the exponential t dependence as afunction of W, the photon-proton c.m. energy, for data from J/PSI muon decay.
The total exclusive J/PSI photoproduction cross section as a function of W,the photon-proton c.m. energy, for data from J/PSI electron decays.
The differential cross section extrapolated to t=0 and the slope parameter of the exponential t dependence for exclusive J/PSI photoproduction as a function of W, the photon-proton c.m. energy for data from J/PSI electron decays.
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.
Forum