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.
By combining results from the MARK-J at PETRA on Bhabha scattering, μ + μ - and τ + τ - production with recent world data from neutrino-electron scattering experiments, we determine unique values for the leptonic weak neutral current coupling constants g V and g A in the framework of electroweak models containing a single Z 0 . In contrast to previous analyses, we only use data from purely leptonic interactions, and therefore avoid the inherent uncertainties resulting from the use of hadronic targets. From the MARK-J data alone in the context of the standard SU(2) ⊗ U (1) model of Glashow, Weinberg and Salam, we find sin 2 θ W =0.24±0.11.
No description provided.
The measurement of the nonelectromagnetic forward-backward charge asymmetry in the reaction e+e−→μ+μ− at s∼34.6 GeV and in the angular region 0<|cosθ|<0.8 is reported. With a systematic error less than 1%, we observe an asymmetry of (-8.1±2.1)%. This is in agreement with the standard electroweak theory prediction of (-7.6±0.6)%. The weak-current coupling constants are also reported.
No description provided.
The reaction e+e−→μ+μ− has been measured at s=57.77GeV, based on 289.6±2.6 pb−1 data collected with the VENUS detector at TRISTAN. The production cross section is measured in bins of the production angle within an angular acceptance of |cosθ|<~0.75, according to a model-independent definition. The result is consistent with the prediction of the standard electroweak theory. Although a trend in measurements at lower energies that the total cross section tends to be smaller than the prediction remains, the discrepancy is not significant. The model-independent result is converted to the differential cross section in the effective-Born scheme by unfolding photon-radiation effects. This result can be extrapolated to quantities for the full solid angle as σtotEB=30.05±0.59 pb and AFBEB=−0.350±0.017, by imposing an ordinary assumption on the production-angle dependence. The converted results are used to set constraints on extensions of the standard theory. S-matrix parametrization, and possible contributions from contact interactions and heavy neutral-scalar exchanges are examined.
Total cross section and forward backward asymmetry results in the effective-Born scheme.
We have studied the production of charged D ∗ mesons in e + e − annihilation at an average center-of-mass energy of 58.0 GeV. Charged D ∗ mesons were identified using two independent methods; the mass-difference method and the detection of the low transverse-momentum pion. The forward-backward asymmetry of the charm quark production was measured to be A c = −0.61±0.13(stat.)±0.08(syst.). The cross section of inclusive D ∗ production was found to be σ(e + e − →D ∗ ± +X) = 24.5 ± 5.3 ( stat. )±3.0( syst. ) pb. If we assume the standard model prediction for the charm quark production, we obtain the branching ratio for the charm quark to produce a charged D ∗ meson to be Br (c→D ∗+ + X) = (22±5( stat. )±3( syst. ))% .
Forward-backward asymmetry of charm quarks at the lowest order.
The cross section and forward-backward muon charge asymmetry for the e + e − → μ + μ − γ reaction were measured to be σ =2.82±0.35 pb and A =−0.34±0.10 with the VENUS detector at TRISTAN at 〈√ s 〉=59.2GeV for an integrated luminosity of 53.5 pb −1 . The measured cross section agrees with the theoretical prediction. The asymmetry result is consistent with the electroweak prediction but not with the QED prediction at the level of 2 σ .
No description provided.
Total and differential cross sections for the dp --> 3He eta reaction have been measured near threshold for 3He center-of-mass momenta in the range from 17.1 MeV/c to 87.5 MeV/c. The data were taken during a slow ramping of the COSY internal deuteron beam scattered on a proton target detecting the 3He ejectiles with the COSY-11 facility. The forward-backward asymmetries of the differential cross sections deviate clearly from zero for center-of-mass momenta above 50 MeV/c indicating the presence of higher partial waves in the final state. Below 50 MeV/c center-of-mass momenta a fit of the final state enhancement factor to the data of the total cross sections results in the 3He eta scattering length of a = |2.9 +/- 0.6| + i (3.2 +/- 0.4) fm.
Forward-Backward asymmetry for the reaction DEUT P --> HE3 ETA.
The differential and total cross sections for the d+p->3He+eta reaction have been measured in a high precision high statistics COSY-ANKE experiment near threshold using a continuous beam energy ramp up to an excess energy Q of 11.3 MeV with essentially 100% acceptance. The kinematics allowed the mean value of Q to be determined to about 9 keV. Evidence is found for the effects of higher partial waves for Q>4 MeV. The very rapid rise of the total cross section to its maximum value within 0.5 MeV of threshold implies a very large eta-3He scattering length and hence the presence of a quasi-bound state extremely close to threshold.
Angular distribution asymmetry parameter defined as:. SIG(TOTAL)*(1+ASYM*COS(THETA(CM))/4*PI.
A charge asymmetry has been measured in hadron jets from e + e − annihilation at energies between 52 and 61.4 geV (〈√ s 〉=57.6 GeV). The measured asymmetry is A =11.4%±2.2%±2.1% and is consistent with the prediction of the standard model of the electroweak theory. By using the differential cross section, lower limits of the compositeness scale in eeqq contact interactions have been determined to be typically a few TeV at 95% CL.
Data are fully corrected for detector effects, resolution and radiative effects.
The search for an additional heavy gauge boson Z′ is described. The models considered are based on either a superstring-motivated E 6 or on a left-right symmetry and assume a minimal Higgs sector. Cross sections and asymmetries measured with the L3 detector in the vicinity of the Z resonance during the 1990 and 1991 running periods are used to determine limits on the Z-Z′ gauge boson mixing angle and on the Z′ mass. For Z′ masses above the direct limits, we obtain the following allowed ranges of the mixing angle, θ M at the 95% confidence level: −0.004 ⪕ θ M ⪕ 0.015 for the χ model, −0.003 ⪕ θ M ⪕ 0.020 for the ψ model, −0.029 ⪕ θ M ⪕ 0.010 for the η model, −0.002 ⪕ θ M ⪕ 0.020 for the LR model,
Data taken during 1990.
Data taken during 1991.
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