We report on measurements of hadronic and leptonic cross sections and leptonic forward-backward asymmetries performed with the L3 detector in the years 1993-95. A total luminosity of 103 pb^-1 was collected at centre-of-mass energies \sqrt{s} ~ m_Z and \sqrt{s} ~ m_Z +/- 1.8 GeV which corresponds to 2.5 million hadronic and 245 thousand leptonic events selected. These data lead to a significantly improved determination of Z parameters. From the total cross sections, combined with our measurements in 1990-92, we obtain the final results: m_Z = 91189.8 +/- 3.1 MeV, Gamma_Z = 2502.4 +/- 4.2 MeV, Gamma_had = 1741.1 +/- 3.8 MeV, Gamma_l = 84.14 +/- 0.17 MeV. An invisible width of Gamma_inv = 499.1 +/- 2.9 MeV is derived which in the Standard Model yields for the number of light neutrino species N_nu = 2.978 +/- 0.014. Adding our results on the leptonic forward-backward asymmetries and the tau polarisation, the effective vector and axial-vector coupling constants of the neutral weak current to charged leptons are determined to be \bar{g}_V^l = -0.0397 +/- 0.0017 and \bar{g}_A^l = -0.50153 +/- 0.00053.Including our measurements of the Z -> b \bar{b} forward-backward and quark charge asymmetries a value for the effective electroweak mixing angle of sin^2\bar{\theta}_W = 0.23093 +/- 0.00066 is derived. All these measurements are in good agreement with the Standard Model of electroweak interactions. Using all our measurements of electroweak observables an upper limit on the mass of the Standard Model Higgs boson of m_H < 133 GeV is set at 95% confidence level.
Updated values of coupling constants and electroweak mixing angle.
Cross sections for hadron production from the 1993 data. The first DSYS error is the uncorrelated part of the systematic error. The second DSYS error is from the statistical error on the absolute luminosity. In addition there is a fully correlated multiplicative contribution to the systematic error of 0.039 PCT plus an absolute uncertainty of 3.2pb together with an additional error from the absolute luminosity of 0.105 PCT.
Cross sections for hadron production from the 1994 data. The first DSYS error is the uncorrelated part of the systematic error. The second DSYS error is from the statistical error on the absolute luminosity. In addition there is a fully correlated multiplicative contribution to the systematic error of 0.039 PCT plus an absolute uncertainty of 3.2pb together with an additional error from the absolute luminosity of 0.088 PCT.
We are reporting on a new determination of sin 2 ϑ w from the ratio of v μ e to v e scattering cross sections. A new detector designed for this purpose was exposed tothe Wide Band Neutrino Beamof the 450 GeV (CERN SPS. An analysis of data taken in 1987 and 1988 is presented based on 762 v μ e and 1017 v e events. From the ratio of σ( v μ e ) to σ( v μ e ) we determined sin 2 ϑ w =0.233±0.012 ( stat ) ± 0.008 ( syst ) without radiative correction. With radiative correction for m t = m H =100 GeV we find sin 2 ϑ w =0.232±0.012( stat )±0.008( syst ).
Data without electroweak radiative corrections.
Data corrected for electroweak radiative effects with TOP and HIGGS masses 100 GeV.
We have performed a high-statistics measurement of Bhabha scattering and of the production of hadrons in electron-positron annihilation at PETRA energies (12 GeV<~s<~36.7 GeV). Combining the results with measurements of μ+μ− and τ+τ− production enables us to compare our results with electroweak theory. We find sin2θw=0.27±0.08. This is in good agreement with the value obtained from neutrino experiments which were carried out in entirely different kinematic regions.
No description provided.
No description provided.
ASYMMETRY WAS USED.
A high-precision measurement of the differential cross section for Bhabha scattering (e+e−→e+e−) is presented. The measurement was performed with the MAC detector at the PEP storage ring of the Stanford Linear Accelerator Center, at a center-of-mass energy of 29 GeV. Effects due to electroweak interference are observed and agree well with the predictions of the Glashow-Salam-Weinberg model. The agreement between the data and the electroweak prediction rules out substructure of the electron up to mass scales of 1 TeV.
Error contains both statistics and systematics.
No description provided.
No description provided.
Muon-neutrino and -antineutrino scattering off electrons was detected in a 19-ton Al spark chamber, exposed to the wide-band ν (ν¯) beam from the CERN proton synchrotron. The background was determined experimentally. 11 (10) genuine νμ− (ν¯μ−) e scattering events were found. The respective cross sections are (1.1±0.6)×10−42(Eν/GeV) cm2 and (2.2±1.0)×10−42(Eν/GeV) cm2. The analysis excludes a pure V−A interaction, and makes a pure V or A theory improbable. The data agree well with the Salam-Weinberg model and sin2θW=0.35±0.08.
No description provided.
No description provided.
Total and differential cross sections for νμe→νμe and ν¯μe→ν¯μe are measured. Values for the model-independent neutral-current couplings of the electron are found to be gV=−0.107±0.035(stat)±0.028(syst) and gA=−0.514±0.023(stat)±0.028(syst). The electroweak mixing parameter sin2θW is determined to be 0.195±0.018(stat)±0.013(syst). Limits are set for the charge radius and magnetic moment of the neutrino as (〈r2〉)<0.24×10−32 cm2 and fμ<0.85×10−9 Bohr magnetons, respectively.
No description provided.
No description provided.
No description provided.
A total of 22 muon-neutrino-electron elastic-scattering events (νμe→νμe) have been observed in an exposure of the Fermilab 15-foot bubble chamber filled with a heavy neon-hydrogen mixture to a wide-band neutrino beam. The elastic-scattering cross section is measured to be 1.67±0.44×10−42Eν cm2 GeV−1. The value of the weak mixing angle (sin2θW) determined from this cross section, which is consistent with other measurements of this angle, is 0.20−0.05+0.06.
No description provided.
We are reporting an improved determination of the electroweak mixing angle sin 2 Θ w from the ratio of ν μ e to ν μ e scattering cross sections. The CHARM II detector was exposed to neutrino and antineutrino wide band beams at the 450 GeV CERN SPS. Including new data collected in 1989 we have obtained 1316 ± 56 ν μ e and 1453 ± 62 ν μ e events. From the ratio of the visible cross sections we determined sin 2 Θ 0 =0.239 ± 0.009(stat) ± 0.007(syst) without radiative corrections and g V e g A e =0.047 ± 0.046 . Combining this last result with recent results on g A e at LEP we obtain g V e = −0.023 ± 0.023.
Systematic error presented includes error from flux normalization 'F'=1.030+- 0.022, no detaled description of the other sources and of the combination pr ocedure.. 'F'.
Without radiative corrections, systematic error combined in quadrature fromconponents listed under SYSTEMATICS.
With radiative corrections as defined by Marciano-Sirlin scheme, see Phys.Rev.D22(1980)2695, Phys.Rev.Lett.46(1981)163, Phys.Rev.D29(1984)945, Phys.Rev.D31(1985)213E, Nucl.Phys.B217(1983)84. CENTRAL VALUE IS FOR M(TOP)=100 GEV, M(HIGGS)=100 GEV.
An analysis of the forward-backward asymmetry in Z0 decays using data from the Collider Detector at Fermilab at √s =1.8 TeV yields AFB=[5.2±5.9(stat)±0.4(syst)]% and sin2θ¯W =0.228−0.015+0.017(stat)±0.002(syst).
Asymmetry after background and QCD corrections.
SIN2TW derived from asymmetry measurement fully corrected for background and radiative corrections.
We present the first measurement of the left-right asymmetry in Bhabha scattering with a polarized electron beam. The effective electron vector and axial vector couplings to the Z0 are extracted from a combined analysis of the polarized Bhabha scattering data and the left-right asymmetry previously published by this collaboration.
No description provided.
Forum