The reactions ee->ee+pi0+X and ee->ee+K0s+X are studied using data collected at LEP with the L3 detector at centre-of-mass energies between 189 and 202 GeV. Inclusive differential cross sections are measured as a function of the particle transverse momentum pt and the pseudo-rapidity. For pt < 1.5 GeV, the pi0 and K0s differential cross sections are described by an exponential, typical of soft hadronic processes. For pt > 1.5 GeV, the cross sections show the presence of perturbative QCD processes, described by a power-law. The data are compared to Monte Carlo predictions and to NLO QCD calculations.
The PI0 differential cross section as a function of PT.
The PI0 differential cross section as a function of pseudorapidity.
The K0S differential cross section as a function of PT.
The growth and development of “charged particle jets” produced in proton-antiproton collisions at 1.8 TeV are studied over a transverse momentum range from 0.5 GeV/c to 50 GeV/c. A variety of leading (highest transverse momentum) charged jet observables are compared with the QCD Monte Carlo models HERWIG, ISAJET, and PYTHIA. The models describe fairly well the multiplicity distribution of charged particles within the leading charged jet, the size of the leading charged jet, the radial distribution of charged particles and transverse momentum around the leading charged jet direction, and the momentum distribution of charged particles within the leading charged jet. The direction of the leading “charged particle jet” in each event is used to define three regions of η−φ space. The “toward” region contains the leading “charged particle jet,” while the “away” region, on the average, contains the away-side jet. The “transverse” region is perpendicular to the plane of the hard 2-to-2 scattering and is very sensitive to the “underlying event” component of the QCD Monte Carlo models. HERWIG, ISAJET, and PYTHIA with their default parameters do not describe correctly all the properties of the “transverse” region.
Average number of charged particles as a function of the relative azimuthal angle between the individual charged particle and the overall leading jet angle.
Average scalar PT sum of charged particles as a function of the relative azimuthal angle between the individual charged particle for 3 different lower limits of the leading jet PT. and the overall jet angle.
The average number of toward(DPHI < 60 DEG), transverse (DPHI 60 TO 120 DEG) and away (DPHI > 120 DEG) charged particles as a function of the PT of the leading charged jet. The data in this table are from the Min-Bias events.
We present a search for new heavy particles, $X$, which decay via $X \to WZ \to e\nu +jj$ in $p{\bar p}$ collisions at $\sqrt{s}$ = 1.8 TeV. No evidence is found for production of $X$ in 110 pb$^{-1}$ of data collected by the Collider Detector at Fermilab. Limits are set at the 95% C.L. on the mass and the production of new heavy charged vector bosons which decay via $W'\to WZ$ in extended gauge models as a function of the width, $\Gamma (W')$, and mixing factor between the $W'$ and the Standard Model $W$ bosons.
CONST(NAME=XI) is the mixing factor between WPRIME and W-boson.
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 on a measurement of the ratio of the differential cross sections for W and Z boson production as a function of transverse momentum in proton-antiproton collisions at sqrt(s) = 1.8 TeV. This measurement uses data recorded by the D0 detector at the Fermilab Tevatron in 1994-1995. It represents the first investigation of a proposal that ratios between W and Z observables can be calculated reliably using perturbative QCD, even when the individual observables are not. Using the ratio of differential cross sections reduces both experimental and theoretical uncertainties, and can therefore provide smaller overall uncertainties in the measured mass and width of the W boson than current methods used at hadron colliders.
The measured W and Z0 cross sections used to compute the ratio.
The measured ratios of W+-/Z0 cross sections, corrected for the branching ratios BR(W-->e-nue)=0.1073+-0.0025 and BR(Z0-->E+E-)=0.033632+-0.000059 (PDG 2000). The error given is the total error, but note that the 4.3pct error in the luminosity cancels completely in the ratio.
We report on a measurement of the mean charged-particle multiplicity of jets in dijet events with dijet masses in the range 80–630GeV/c2, produced at the Tevatron in pp¯ collisions with s=1.8TeV and recorded by the Collider Detector at Fermilab. The data are fit to perturbative-QCD calculations carried out in the framework of the modified leading log approximation and the hypothesis of local parton-hadron duality. The fit yields values for two parameters in that framework: the ratio of parton multiplicities in gluon and quark jets, $r≡N_{partons}^{g−jet} / N_{partons}^{q−jet} = 1.7 \pm 0.3$, and the ratio of the number of charged hadrons to the number of partons in a jet, $K_{LPHD}^{charged} ≡ N_{hadrons}^{charged} / N_{partons} = 0.57 \pm 0.11$.
Measured values of inclusive charged particle multiplicity per jet for jets falling in restricted cones with opening angles 0.17, 0.28 and 0.47 radians. Note that the systematic errors are strongly correlated.
We report the first observation of diffractive $J/\psi(\to \mu^+\mu^-)$ production in $\bar pp$ collisions at $\sqrt{s}$=1.8 TeV. Diffractive events are identified by their rapidity gap signature. In a sample of events with two muons of transverse momentum $p_T^{\mu}>2$ GeV/$c$ within the pseudorapidity region $|\eta|<$1.0, the ratio of diffractive to total $J/\psi$ production rates is found to be $R_{J/\psi}= [1.45\pm 0.25]%$. The ratio $R_{J/\psi}(x)$ is presented as a function of $x$-Bjorken. By combining it with our previously measured corresponding ratio $R_{jj}(x)$ for diffractive dijet production, we extract a value of $0.59\pm 0.15$ for the gluon fraction of the diffractive structure function of the proton.
Diffractive to total J/psi production ratio.
Ratio of diffractive to total J/psi rate, per unit of the fractional momentum loss of the leading (anti)proton, and as a function of x-Bjorken of the struck parton of the (anti)proton adjacent to the rapidity gap and participating in the J/psi production.
Gluon fraction of the diffractive structure function of the (anti)proton.
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 production of $J/\psi$ mesons in continuum $e^+e^-$ annihilations has been studied with the BABAR detector at energies near the $\Upsilon(4S)$ resonance, approximately 10.6 GeV. The mesons are distinguished from $J/\psi$ production in B decays through their center-of-mass momentum and energy. We measure the cross section $e^+e^-\to J/\psi X$ to be $2.52\pm 0.21\pm 0.21$ pb: for momentum above 2 GeV/c, it is $1.87\pm 0.10\pm 0.15$ pb. We set a 90% confidence level upper limit on the branching fraction for direct $\Upsilon(4S)$\to J/\psi X$ decays at $4.7\times 10^{-4}$.
Cross section measurement.