We report on a measurement of the mass of the Z 0 boson, its total width, and its partial decay widths into hadrons and leptons. On the basis of 25 801 hadronic decays and 1999 decays into electrons, muons or taus, selected over eleven energy points between 88.28 GeV and 95.04 GeV, we obtain from a combined fit to hadrons and leptons a mass of M z =91.154±0.021 (exp)±0.030 (LEP) GeV, and a total width of Γ z =2.536±0.045 GeV. The errors on M z have been separated into the experimental error and the uncertainty due to the LEP beam energy. The measured leptonic partial widths are Γ ee =81.2±2.6 MeV, Γ μμ =82.6± 5.8 MeV, and Γ ττ =85.7±7.1 MeV, consistent with lepton universality. From a fit assuming lepton universality we obtain Γ ℓ + ℓ − = 81.9±2.0 MeV. The hadronic partial width is Γ had =1838±46 MeV. From the measured total and partial widths a model independent value for the invisible width is calculated to be Γ inv =453±44 MeV. The errors quoted include both the statistical and the systematic uncertainties.
Errors are statistical and point to point systematic luminosity error of 1 pct.
Measured values of e+ e- --> e+ e- cross section.
Corrected cross section. Corrections are for t-channel effects and loss of acollinear events near the boundary of the acceptance.
Using BEBC equipped with a hydrogen-filled neon-surrounded track-sensitive target, the charged current cross sections and structure functions of hydrogen and neon targets traversed by the same neutrinos and antineutrinos are compared directly. The measured total cross-section ratios between hydrogen and neon allow precise total cross-section values for hydrogen to be inferred. Using this normalization, the ν and ν hydrogen data are combined and the quark distributions in free nucleons, parametrised as functions of ξ, are extracted. This free-nucleon parametrisation is then compared directly with the neon data in order to measure nuclear effects such as those recently reported by the EMC collaboration. Only small effects are seen, in excellent agreement with recent SLAC data in a more similar A and q 2 range.
Measured charged current total cross section.
Measured charged current total cross section.
AVERAGE Q**2 IS 6.9GEV**2 FOR NU AND 4.3GEV**2 FOR ANU.
We have measured the partial width and forward-backward charge asymmetry for the reaction e + e - →Z 0 →μ + μ - (γ). We obtain a partial width Γ μμ of 83.3±1.3(stat)±0.9(sys) MeV and the following values for the vector and axial vector couplings: g v =−0.062 −0.015 +0.020 and g A =−0.497 −0.005 +0.005 . From our measurement of the partial width and the mass of the Z 0 boson we determine the effective electroweak mixing angle, sin 2 θ w =0.232±0.005, and the neutral current coupling strength parameter, ϱ =0.998±0.016.
No description provided.
Forward backward charge asymmetry.
No description provided.
The Beijing Spectrometer (BES) experiment has observed purely leptonic decays of the Ds meson in the reaction e+e−→Ds+Ds− at a c.m. energy of 4.03 GeV. Three events are observed in which one Ds decays hadronically to φπ, K¯*0K, or K¯0K, and the other decays leptonically to μνμ or τντ. With the assumption of μ−τ universality, values of the branching fraction, B(Ds→μνμ)=(1.5−0.6−0.2+1.3+0.3)%, and the Ds pseudoscalar decay constant, fDs=(4.3−1.3−0.4+1.5+0.4)×102 MeV, are obtained.
No description provided.
In this table CONST is the pseudoscalar decay constant, f_[D/S].
None
No description provided.
No description provided.
No description provided.
We have measured the photon yield in lepton pair events recorded by the OPAL detector in a data sample corresponding to an integrated luminosity of 7.1 pb −1 at centre-of-mass energies between 88 GeV and 94 GeV. The results are compared to QED expectations for initial and final state photon radiation. No anomalous photon yield has been found, and stringent limits on the branching ratio for exotic radiative three body Z 0 decays into a photon and a pair of leptons are obtained. We also place limits on possible Z 0 decays into a photon and a resonance X with subsequent decays of X into a pair of leptons. Acollinear μ + μ − events with missing momentum along the beam direction are identified as events with hard initial state photon radiation and used to measure an average cross section of 15 ± 8 6 pb for e + e − annihilation into μ + μ − , in the so far untested range of centre-of-mass energies between 60 GeV and 84 GeV. This value is consistent with a cross section of 24 pb, expected from Z 0 and photon exchange.
No description provided.
The e + e − → μ + μ − reaction has been studied at centre of mass energies ranging between 38.3 abd 46.8 GeV with the CELLO detector at PETRA. We present results on the cross section and the charge asymmetry for this channel. Combining all the data at the average energy 〈 s 〉=43 GeV we obtain R μμ =〈 σ μμ / σ 0 〉=0.98±0.04±0.04, 〈 A μμ 〉=(−14.1±3.7±1.0)%, where σ 0 is the QED cross section and A μμ is the charge asymmetry corrected for pure radiative effects. These results are in good agreement with the expected values of R μμ =1.01 and A μμ =−14.5% at that energy.
Mu-pair cross sections.
Corrected angular distributions with data sample divided into two energy regions with means 39 and 44 GeV and total energy region.
Forward-backward asymmetry.
Ratios of the Psi' over the J/psi production cross sections in the dilepton channel for C, Ti and W targets have been measured in 920 GeV proton-nucleus interactions with the HERA-B detector at the HERA storage ring. The Psi' and J/psi states were reconstructed in both the mu+mu- and the e+e- decay modes. The measurements covered the kinematic range -0.35 < x_F < 0.1 with transverse momentum p_T < 4.5 GeV/c. The Psi' to J/psi production ratio is almost constant in the covered x_F range and shows a slow increase with p_T. The angular dependence of the ratio has been used to measure the difference of the Psi' and J/psi polarization. All results for the muon and electron decay channels are in good agreement: their ratio, averaged over all events, is R_psi'(mu)/R_psi'(e)=1.00+-0.08+-0.04. This result constitutes a new, direct experimental constraint on the double ratio of branching fractions, (B'(mu)*B(e))/(B(mu)*B'(e)), of Psi' and J/psi in the two channels.
Ratio of PSI(3685) and J/PSI cross sections for both muon and electron channels combined, obtained for different cos theta in the s-channel helicity frame.
Ratio of PSI(3685) and J/PSI cross sections for both muon and electron channels combined, obtained for intervals inpT using the data from all targets.
Ratio of PSI(3685) and J/PSI production cross sections per nucleus.
A sample of 25000 Z 0 → τ + τ − events collected by the DELPHI experiment at LEP in 1991 and 1992 is used to measure the leptonic branching fractions of the τ lepton. The results are B(τ → eν ν ) = (17.51 ± 0.39) % and B(τ → μν ν ) = (17.02 ± 0.31) %. The ratio of the muon and electron couplings to the weak charged current is measured to be g μ g e = 1.000 ± 0.013 , satisfying e-μ universality. The leptonic branching fraction corrected to the value for a massless lepton, assuming e-μ universality, is found to be B(τ → lν ν ) = (17.50 ± 0.25) %.
Axis error includes +- 0.23/0.23 contribution (Data statistics).
Axis error includes +- 0.19/0.19 contribution (Data statistics).
Combined from the two branching fractions above. E-MU universality assumed.
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.
Forum