We report the first measurements of the kurtosis (\kappa), skewness (S) and variance (\sigma^2) of net-proton multiplicity (N_p - N_pbar) distributions at midrapidity for Au+Au collisions at \sqrt(s_NN) = 19.6, 62.4, and 200 GeV corresponding to baryon chemical potentials (\mu_B) between 200 - 20 MeV. Our measurements of the products \kappa \sigma^2 and S \sigma, which can be related to theoretical calculations sensitive to baryon number susceptibilities and long range correlations, are constant as functions of collision centrality. We compare these products with results from lattice QCD and various models without a critical point and study the \sqrt(s_NN) dependence of \kappa \sigma^2. From the measurements at the three beam energies, we find no evidence for a critical point in the QCD phase diagram for \mu_B below 200 MeV.
$\Delta N_p$ multiplicity distribution in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV for 0-5 percent central collisions at midrapidity (| y |< 0.5).
$\Delta N_p$ multiplicity distribution in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV for 30-40 percent central collisions at midrapidity (| y |< 0.5).
$\Delta N_p$ multiplicity distribution in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV for 70-80 percent central collisions at midrapidity (| y |< 0.5).
We present the first experimental results based on the jet boost algorithm, a technique to select unbiased samples of gluon jets in e+e- annihilations, i.e. gluon jets free of biases introduced by event selection or jet finding criteria. Our results are derived from hadronic Z0 decays observed with the OPAL detector at the LEP e+e- collider at CERN. First, we test the boost algorithm through studies with Herwig Monte Carlo events and find that it provides accurate measurements of the charged particle multiplicity distributions of unbiased gluon jets for jet energies larger than about 5 GeV, and of the jet particle energy spectra (fragmentation functions) for jet energies larger than about 14 GeV. Second, we apply the boost algorithm to our data to derive unbiased measurements of the gluon jet multiplicity distribution for energies between about 5 and 18 GeV, and of the gluon jet fragmentation function at 14 and 18 GeV. In conjunction with our earlier results at 40 GeV, we then test QCD calculations for the energy evolution of the distributions, specifically the mean and first two non-trivial normalized factorial moments of the multiplicity distribution, and the fragmentation function. The theoretical results are found to be in global agreement with the data, although the factorial moments are not well described for jet energies below about 14 GeV.
The charged particle multiplicity distribution of gluon jets, $n_{\rm gluon}^{\rm ch.}$, for $E_{\rm g}^*$$\,=\,$5.25, 5.98 and 6.98 GeV. The data have been corrected for detector acceptance and resolution, for event selection, and for gluon jet impurity.
The charged particle multiplicity distribution of gluon jets, $n_{\rm gluon}^{\rm ch.}$, for $E_{\rm g}^*$$\,=\,$8.43 and 10.92 GeV. The data have been corrected for detector acceptance and resolution, for event selection, and for gluon jet impurity.
The charged particle multiplicity distribution of gluon jets, $n_{\rm gluon}^{\rm ch.}$, for $E_{\rm g}^*$$\,=\,$14.24 and 17.72 GeV. The data have been corrected for detector acceptance and resolution, for event selection, and for gluon jet impurity.
The charged particle multiplicities of two- and three-jet events from the reaction e+e- -> Z0 -> hadrons are measured for Z0 decays to light quark (uds) flavors. Using recent theoretical expressions to account for biases from event selection, results corresponding to unbiased gluon jets are extracted over a range of jet energies from about 11 to 30 GeV. We find consistency between these results and direct measurements of unbiased gluon jet multiplicity from upsilon and Z0 decays. The unbiased gluon jet data including the direct measurements are compared to corresponding results for quark jets. We perform fits based on analytic expressions for particle multiplicity in jets to determine the ratio r = Ng/Nq of multiplicities between gluon and quark jets as a function of energy. We also determine the ratio of slopes, r(1) = (dNg/dy)/(dNq/dy), and of curvatures, r(2) = (d2Ng/dy2)/(d2Nq/dy2), where y specifies the energy scale. At 30 GeV, we find r = 1.422 +/- 0.051, r(1) = 1.761 +/- 0.071 and r(2) = 1.98 +/- 0.13, where the uncertainties are the statistical and systematic terms added in quadrature. These results are in general agreement with theoretical predictions. In addition, we use the measurements of the energy dependence of Ng and Nq to determine an effective value of the ratio of QCD color factors, CA/CF. Our result, CA/CF = 2.23 +/- 0.14 (total), is consistent with the QCD value of 2.25.
Measurements of the mean charged particle multiplicity of biased two-jet uds flavour events from Z0 decays as a function of the transverse momentum cutoff PT(C=LU) used to separate two- and three-jet events.
Measurements of the mean charged particle multiplicity of three-jet uds flavour 'Y events' from Z0 decays, as a function of the angle THETA1 between the lowest two energy jets. The results for the quark jet scale SQRT(S(C=QQBAR)) and the gluon jet scales PT(C=LU) and PT(C=LE) are also given.
Measurements of the unbiased gluon multiplicity as a function of the energy scale Q=PT(C=LU). The corresponding bins of THETA1 in 'Y events' are also indicated.
About 4.4 million hadronic decays of Z bosons, recorded by the OPAL detector at LEP at a centre-of-mass energy of around sqrt(s) = 91.2 GeV, are used to determine the mean charged particle multiplicities for the three light quark flavours. Events from primary u, d, and s quarks are tagged by selecting characteristic particles which carry a large fraction of the beam energy. The charged particle multiplicities are measured in the hemispheres opposite to these particles. An unfolding procedure is applied to obtain these multiplicities for each primary light quark flavour. This yields <n_u> = 17.77 +- 0.51 +0.86 -1.20, <n_d> = 21.44 +- 0.63 +1.46 -1.17, <n_s> = 20.02 +- 0.13 +0.39 -0.37, where statistical and systematic errors are given. The results for <n_u> and <n_d> are almost fully statistically anti-correlated. Within the errors the result is consistent with the flavour independence of the strong interaction for the particle multiplicities in events from the light up, down, and strange quarks.
No description provided.
No description provided.
We employ data taken by the JADE and OPAL experiments for an integrated QCD study in hadronic e+e- annihilations at c.m.s. energies ranging from 35 GeV through 189 GeV. The study is based on jet-multiplicity related observables. The observables are obtained to high jet resolution scales with the JADE, Durham, Cambridge and cone jet finders, and compared with the predictions of various QCD and Monte Carlo models. The strong coupling strength, alpha_s, is determined at each energy by fits of O(alpha_s^2) calculations, as well as matched O(alpha_s^2) and NLLA predictions, to the data. Matching schemes are compared, and the dependence of the results on the choice of the renormalization scale is investigated. The combination of the results using matched predictions gives alpha_s(MZ)=0.1187+{0.0034}-{0.0019}. The strong coupling is also obtained, at lower precision, from O(alpha_s^2) fits of the c.m.s. energy evolution of some of the observables. A qualitative comparison is made between the data and a recent MLLA prediction for mean jet multiplicities.
Overall result for ALPHAS at the Z0 mass from the combination of the ln R-matching results from the observables evolved using a three-loop running expression. The errors shown are total errors and contain all the statistics and systematics.
Weighted mean for ALPHAS at the Z0 mass determined from the energy evolutions of the mean values of the 2-jet cross sections obtained with the JADE and DURHAMschemes and the 3-jet fraction for the JADE, DURHAM and CAMBRIDGE schemes evaluted at a fixed YCUT.. The errors shown are total errors and contain all the statistics and systematics.
Combined results for ALPHA_S from fits of matched predicitions. The first systematic (DSYS) error is the experimental systematic, the second DSYS error isthe hadronization systematic and the third is the QCD scale error. The values of ALPHAS evolved to the Z0 mass using a three-loop evolution are also given.
We have studied hadronic events from e+e- annihilation data at centre-of-mass energies of sqrt{s}=172, 183 and 189 GeV. The total integrated luminosity of the three samples, measured with the OPAL detector, corresponds to 250 pb^-1. We present distributions of event shape variables, charged particle multiplicity and momentum, measured separately in the three data samples. From these we extract measurements of the strong coupling alpha_s, the mean charged particle multiplicity <nch> and the peak position xi_0 in the xi_p=ln(1/x_p) distribution. In general the data are described well by analytic QCD calculations and Monte Carlo models. Our measured values of alpha_s, <nch> and xi_0 are consistent with previous determinations at sqrt{s}=MZ.
Distribution of Thrust.
Distribution of Thrust Major.
Distribution of Thrust Minor.
We have used the CLEO II detector to study the multiplicity of charged particles in the decays of B mesons produced at the $\Upsilon(4S)$ resonance. Using a sample of 1.5 x 10^6 B meson pairs, we find the mean inclusive charged particle multiplicity to be 10.71 +- 0.02 +0.21/-0.15 for the decay of the pair. This corresponds to a mean multiplicity of 5.36 +- 0.01 +0.11/-0.08 for a single B meson. Using the same data sample, we have also extracted the mean multiplicities in semileptonic and nonleptonic decays. We measure a mean of 7.82 +- 0.05 +0.21/-0.19 charged particles per $B\bar{B}$ decay when both mesons decay semileptonically. When neither B meson decays semileptonically, we measure a mean charged particle multiplicity of 11.62 +- 0.04 +0.24/-0.18 per $B\bar{B}$ pair.
Charged track multiplicity (i.e. charged hadron and charged lepton) in B meson decay.
Fragmentation functions for charged particles in Z -> qq(bar) events have been measured for bottom (b), charm (c) and light (uds) quarks as well as for all flavours together. The results are based on data recorded between 1990 and 1995 using the OPAL detector at LEP. Event samples with different flavour compositions were formed using reconstructed D* mesons and secondary vertices. The \xi_p = ln(1/x_E) distributions and the position of their maxima \xi_max are also presented separately for uds, c and b quark events. The fragmentation function for b quarks is significantly softer than for uds quarks.
Fragmentation function for 'uds-quark' events.
Fragmentation function for 'c-quark' events.
Fragmentation function for 'b-quark' events.
The inclusive production rates and differential cross-sections of photons and mesons with a final state containing photons have been measured with the OPAL detector at LEP. The light mesons covered by the measurements are the \pi^0, \eta, \rho(770)+-, \omega(782), \eta'(958) and a_0(980)+-. The particle multiplicities per hadronic Z^0 decay, extrapolated to the full energy range, are: <n_\gamma> = 20.97 +/- 0.02 +/- 1.15, <n_\pi^0> = 9.55 +/- 0.06 +/- 0.75, <n_\eta> = 0.97 +/- 0.03 +/- 0.11, <n_\rho^+-> = 2.40 +/- 0.06 +/- 0.43, <n_\omega> = 1.04 +/- 0.04 +/- 0.14, <n_\eta> = 0.14 +/- 0.01 +/- 0.02, <n_a_0+-> = 0.27 +/- 0.04 +/- 0.10. where the first errors are statistical and the second systematic. In general, the results are in agreement with the predictions of the JETSET and HERWIG Monte Carlo models.
Particle multiplicities per hadronic decay extrapolated to the full energy range.
Photon fragmentation function.
Photon fragmentation function.
The production rates of D^*+/- mesons in charm and bottom events at centre-of-mass energies of about 91 GeV and the partial width of primary cc(bar) pairs in hadronic Z^0 decays have been measured at LEP using almost 4.4 million hadronic Z^0 decays collected with the OPAL detector between 1990 and 1995. Using a combination of several charm quark tagging methods based on fully and partially reconstructed D^*+/- mesons, and a bottom tag based on identified muons and electrons, the hadronisation fractions of charm and bottom quarks into D^*+/- mesons have been found to be: f(b -> D^*+ X) = 0.173 +/- 0.016 +/- 0.012 and f(c -> D^*+ X) = 0.222 +/- 0.014 +/- 0.014 The fraction of cc(bar) events in hadronic Z^0 decays, Gamma_cc(bar)/Gamma_had = Gamma(Z^0 -> cc(bar))/Gamma(Z^0 -> hadrons), is determined to be Gamma_cc(bar)/Gamma_had = 0.180 +/- 0.011 +/- 0.012 +/- 0.006 In all cases the first error is statistical, and the second one systematic. The last error quoted for Gamma_cc(bar)/Gamma_had is due to external branching ratios.
No description provided.
No description provided.
The second syst. errors results due to extranal branching ratios. Charge conjugated states are implied. FD is considered as a quark fragmentation fraction. Sqrt(s(E+ E-)) = 91.2 GeV.
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