A search for the 0 + → 2 + neutrinoless double-beta decay of 76 Ge into the first excited state of 76 Se has been carried out using a coincidence technique between Ge and NaI detectors. Since the expected number of counts is very small and mixed with a continuous background of natural radioactivity, special care has been taken to maintain the good energy resolution of the detectors. As a consequence, the experimental data display, after 6207 h statistical time, a coincidence signal of 19.3 ± 5.8 counts, between an energy deposition of 1484.0 ± 0.3 keV in the Ge detectors and 561 ± 10 keV in the NaI detectors. Both Ge and NaI energies are within the experimental errors, compatible with the expected values. No other unidentified coincidence signal has been found in the full Ge-NaI energy matrix, and no similar γγ cascade has been found within our background. Even if the low statistics does not completely rule out the possibility of a statistical fluctuation, this result should encourage further experiments with improved sensitivities.
SE76* IS IN 2+ EXGITED STATE.
In an experiment using the CERN SPS hyperon beam, we have measured the cross sections for inclusive production of Ξ0 (accompanied by a charged particle), Ξ(1530)- and Ξ(1530)0 in Ξ--beryllium collisions at 116 GeV/c. All differential cross sections are found to be well described by the from (1−xF)n exp (−bpT2) over the whole accessible kinematical region (xF>0.3). The invariant production spectra for Ξ0, Ξ(1530)- and Ξ(1530)0, as well as those for Ξ-, and Ω- (obtained previously from the same data), are compared to theoretical predictions deduced from a two-component quark-diquark cascade model.
Total Inelastic Cross Section. This is an estimate based on the measurements of N BE --> INELASTIC and N P --> INELASTIC (T J Roberts et al., NP B159 (1979), 56) and the measurement of XI- P --> INELASTIC (S F Biagi et al., NP B186 (1981), 1).
The XI- and OMEGA- data were computed from Biagi et al., ZP C34 (87) 187.
The first kinematically complete, good-statistics data for the (π,2π) reaction on the proton are presented. They involve double- and triple-differential cross sections as well as π+π− angular correlations. At energies around the Δ resonance, they exhibit a marked difference from phase space. The data are qualitatively described within the framework of an extension of Weinberg’s effective chiral Lagrangian.
No description provided.
No description provided.
More extensive and precise results are reported on the parameters of Z decay. On the basis of 20 000 Z decays collected with the ALEPH detector at LEP we find M z =91.182±0.026 (exp.) ±0.030 (beam) GeV, Γ z =2.541±0.056 GeV and σ had 0 =41.4±0.8 nb. The partial widths for the hadronic and leptonic channels are Γ had =1804±44 MeV, Γ e + e − =82.1±3.4 MeV, Γ μ + μ − =87.9±6.0 MeV and Γ τ + τ − =86.1±5.6 MeV, in good agreement with the standard model. On the basis of the average leptonic width Γ ℓ + ℓ − =83.9±2.2 MeV, the effective weak mixing angle is found to be sin 2 θ w ( M z )=0.231±0.008. Usin g the partial widths calculated in the standard model, the number of light neutrino families is N ν =3.01±0.15 (exp.)±0.05 (theor.).
Penetrating charged particle track selection.
Calorimeter selection.
Average cross section.
We have made a precise measurement of the cross section for e + e − →Z 0 →hadrons with the L3 detector at LEP, covering the s range from 88.28 to 95.04 GeV. From a fit to the Z 0 mass, total width, and the hadronic cross section to be M Z 0 =91.160 ± 0.024 (experiment) ±0.030(LEP) GeV, Γ Z 0 =2.539±0.054 GeV, and σ h ( M Z 0 )=29.5±0.7 nb. We also used the fit to the Z 0 peak cross section and the width todetermine Γ invisible =0.548±0.029 GeV, which corresponds to 3.29±0.17 species of light neutrinos. The possibility of four or more neutrino flavors is thus ruled out at the 4σ confidence level.
No description provided.
Total hadronic cross section.
We report on a measurement of the processes e + e − →e + e − , e + e − → μ + μ − , and e + e − → τ + τ − near the Z 0 pole. On the basis of 163 e + e − , 101 μ + μ − and 87 τ + τ − events we obtain Γ ee =89±4±4 MeV, Γ μμ =85±9±6 MeV and Γ ττ =87±10±8 MeV, compatible with the standard model. Combining these with our previous results on hadronic Z 0 decays, we find a hadronic width Γ had =1787±81±90 MeV and an invisible width Γ inv =552±85±71 MeV.
Statistical errors only.
Statistical errors only.
We have measured both the rates and the forward-backward asymmetry of ℓ + ℓ − from Z 0 →ℓ + ℓ − (where ℓ= μ , τ ) with the L3 detector. We obtained Γ ℓℓ =88±4±3 MeV and the vector neutral current coupling constant, g v =0.00±0.07 and the axial vector neutral current coupling constant, g A =−0.515±0.015.
No description provided.
No description provided.
We report on a search for new quarks in hadronic Z° decays. From the event shape analysis of a data sample containing 2185 multihadronic annihilation events, we observe no evidence for the top or b' quarks. We derive limits for the top and b' quark masses under the assumption of various possible standard model and non-standard model decay schemes. Our search is sensitive to quark masses larger than 23 GeV/ c 2 ; it yields the following lower limits at a 95% confidence level: 44.5 GeV/ c 2 for the top quark mass and 45.2 GeV/ c 2 for the b′ quark mass.
Measured event shape distributions - uncorrected.
Relative production rates of multijet hadronic final states of Z 0 boson decays, observed in e + e − annihilation around 91 GeV centre of mass energy, are presented. The data can be well described by analytic O( α s 2 ) QCD calculations and by QCD shower model calaculations with parameters as determined at lower energies. A first judgement of Λ MS and of the renormalization scale μ 2 in O( α s 2 ) QCD results in values similar to those obtained in the continuum of e + e − annihilations. Significant scaling violations are observed when the 3-jet fractions are compared to the corresponding results from smaller centre of mass energies. They can be interpreted as being entirely due tot the energy dependence of α s , as proposed by the nonabelian nature of QCD, The possibility of an energy independent coupling constant can be excluded with a significance of 5.7 standard deviations.
Data are corrected for final acceptance and resolution of the detector. No explicit corrections for hadronisation effects are applied.
We present an analysis of strange particle production frome+e− annihilation into multihadronic final states. The experiment was performed with the CELLO detector at the PETRA storage ring at DESY, the data was taken at a centre of mass energy of 35 GeV with an integrated luminosity of 86 pb−1. The particlesKS0,K*± and Λ have been identified by their characteristic decays, and differential cross sections for their production have been obtained. From a comparison ofKS0 andK*± rates the Lund vector meson suppression parameterV/(V+P)S has been determined.
Errors are statistical only.
Errors are statistical only.
Errors are statistical only.
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