The energy and centrality dependence of local particle pseudorapidity densities as well as validity of various parametrizations of the distributions are examined. The dispersion, σ, of the rapidity density distribution of produced particles varies slowly with centrality and is 0.80, 0.98, 1.21 and 1.41 for central interactions at 3.7, 14.6, 60 and 200A GeV incident energy, respectively, σ is found to be independent of the size of the interacting system at fixed energy. A novel way of representing the window dependence of the multiplicity as normalized variance versus inverse average multiplicity is outlined.
No description provided.
NUCLEUS IS AGBR, CENTRAL EVENTS.
No description provided.
A systematic study of inclusive pion double charge exchange is reported for nuclei between A=16 and A=208. The doubly differential cross sections for the A(π+,π−) and A(π−,π+) reactions in O16, Ca40, Rh103, and Pb208 were measured at incident energies between 120 and 270 MeV at three to five outgoing pion angles. Pion spectra were measured over the energy range from 10 MeV to the kinematic limit for double charge exchange. Integrating these spectra over outgoing pion energy generated angular distributions, and subsequently integrating these angular distributions generated total reaction cross sections. The shapes of the measured spectra are compared with those determined by the distribution of events in four-body phase space and with those predicted by a model in which the pion undergoes two sequential single charge exchanges on nucleons in a Fermi gas. The cross sections are compared with predictions of cascade calculations in which more than two interactions, including pion absorption and scattering without charge exchange, may occur.
No description provided.
From a sample of 150 000 hadronic Z decays collected with the ALEPH detector at LEP, events containing prompt leptons are used to measure the forward-backward asymmetries for the channels Z → b b and Z → c c , giving the results A FB b =0.126±0.028±0.012 and A FB c =0.064±0.039±0.030. These asymmetries correspond to the value of effective electroweak mixing angle at the Z mass sin 2 θ W ( m Z 2 ) = 0.2262±0.0053.
b asymmetry from high pt leptons.
b asymmetry from full pt range.
b asymmetry from full pt range.
A significant charge asymmetry is observed in the hadronic Z decays with the ALEPH detector at LEP. The asymmetry expressed in terms of the difference in momentum weighted charges in the two event hemispheres is measured to be < Q forward >−< Q backward >= −0.0084±0.0015 (stat.) ±0.0004 (exp. sys.). In the framework of the standard model this can be interpreted as a measurement of the effective electroweak mixing angle, sin 2 O w ( M z 2 =0.2300±0.0034 (stat.) ±0.0010 (exp. sys.) ±0.0038 (theor. sys.) or of the ratio of the vector to axual- vector coupling costants of the electron, g ve g Ae =+0.073±0.024.
No description provided.
No description provided.
The production of μ−e+ dileptons by muon neutrinos is studied in a high-statistics bubble-chamber experiment. The experiment consisted of exposing the Fermilab 15-ft bubble chamber filled with a heavy Ne-H2 mix to a wideband neutrino beam. In a total sample of 146 700±11 700 charged-current interactions, 461 events with an e+(Pe+>300 MeV/c) and a μ− are observed. The rate for μ−e+ dilepton production in measured to be (0.42±0.06)%. The energy dependence of this rate is presented. The kinematic distributions for the μ−e+ events are consistent with charm production and subsequent semileptonic decay. A total of 60 KS0 and 31 Λ0 decays were observed in the μ−e+ event sample. The measured rates for neutral-strange-particle production are 0.78±0.12 K0K¯0's and 0.19±0.04 Λ0's per μ−e+ event. Finally, rates for Λc+, D0, and D+ production in charged-current νμ interactions are derived. They are found to be (4−2+10)%, (1.7−0.7+0.5)%, and (1.3−0.5+0.4)%, respectively.
No description provided.
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We examine the negative 3π final state produced in association with Δ++(1232) in the reaction γp→Δ++π+π−π− at an incident photon energy of 19.3 GeV. The most prominent enhancement in the 3π spectrum occurs at a mass and with a width consistent with the parameters of the a2(1320). This identification is confirmed by the various angular distributions. The a2 production cross section, corrected for efficiencies and alternate a2 decay modes, is 0.45±0.05 μb.
No description provided.
Using 106 000 hadronic events obtained with the ALEPH detector at LEP at energies close to the Z resonance peak, the strong coupling constant α s is measured by an analysis of energy-energy correlations (EEC) and the global event shape variables thrust, C -parameter and oblateness. It is shown that the theoretical uncertainties can be significantly reduced if the final state particles are first combined in clusters using a minimum scaled invariant mass cut, Y cut , before these variables are computed. The combined result from all shape variables of pre-clustered events is α s ( M Z 2 = 0.117±0.005 for a renormalization scale μ= 1 2 M Z . For μ values between M Z and the b-quark mass, the result changes by −0.009 +0.006 .
No description provided.
Error contains both experimental and theoretical errors.
The production of the neutralK− (892) resonances by 200 GeVK− andπ− has been studied over the kinematic range 0.0<xf<1.0 andpt2<5.0 GeV2. Longitudinal and transverse momentum distributions are presented. In addition the decay angular distributions inK− fragmentation to\(\bar K^{0*} \) have been investigated.
No description provided.
No description provided.
No description provided.
An analysis of global event-shape variables has been carried out for the reaction e + e − →Z 0 →hadrons to measure the strong coupling constant α s . This study is based on 52 720 hadronic events obtained in 1989/90 with the ALEPH detector at the LEP collider at energies near the peak of the Z-resonance. In order to determine α s , second order QCD predictions modified by effects of perturbative higher orders and hadronization were fitted to the experimental distributions of event-shape variables. From a detailed analysis of the theoretical uncertainties we find that this approach is best justified for the differential two-jet rate, from which we obtain α s ( M Z 2 ) = 0.121 ± 0.002(stat.)±0.003(sys.)±0.007(theor.) using a renormalization scale ω = 1 2 M Z . The dependence of α s ( M Z 2 ) on ω is parameterized. For scales m b <ω< M Z the result varies by −0.012 +0.007 .
The second DSYS error is the theoretical error.
We have measured the production polarization and magnetic moment of a sample of 89×103Ξ− hyperons produced in the inclusive reaction p(400 GeV/c)+Cu→Ξ−+X. The weighted average of the polarization is -0.070±0.008±0.010 at a pt of 0.63 GeV/c. The Ξ−'s magnetic moment yields the value μΞ=−0.661±0.036±0.036 nuclear magnetons. The first error is statistical, the second systematic.
No description provided.
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