The differential cross section of the reactione+e−→e+e− at a c.m. energy of 34.7 GeV has been measured. The result, together with our previously measurede+e−→α+α− data, are compared with the standard model predictions. We obtain for the weak neutral current couplings the valuesgv2=0.09×0.06,ga2=0.38×0.08. A fit of the Weinberg mixing angle gives the valuegv2=0.09×0.06,ga2=0.038×0.08. The data are also used to set limits on possible deviations from the pointlike structure of leptons. An upper limit for thee+e− coupling to a heavy spin 0 boson is also given.
Fully corrected results for Bhabha scattering.
The differential cross section for Bhabha scattering.
The external beam of the 2.5 GeV-electron-synchrotron has been used to measre elastic electron proton scattering at four-momentum-transfers between 15 and 50 fm −2 . By combining these results with measurements at small angles at DESY, we have obtained the electric and magnetic form factors separately. Their ratio shows a deviation from the scaling law.
No description provided.
No description provided.
We have studied 419 τ pair events produced in the reactione+e−→τ+ τ− at a c.m. energy of 34.6 GeV. We measure the cross section and angular distribution, as well as the decay branching ratios. The production characteristics are consistent with the Standard Electroweak Model predictions of γ andZ0 interference. The branching ratios are generally consistent with the τ decaying according to standard weak interaction principles, but we observe somewhat more decays resulting in single charged hadrons plus neutrals than are predicted by present theory.
Measured cross section relative to Standard Model Prediction.
Asymmetry based on fits to angular distribution.
Backward elastic scattering has been measured for π + p at 2.85 and 3.30 GeV/ c and for π − p at 3.30 GeV/ c . The π + p angular distributions show steep backward peaks, whereas the π − p distribution is flatter. At 2.85 GeV/ c the π + p differential cross section close to 180° is more than twice that at 3.30 GeV/ c , supporting the assignment J P = 11 2 + for Δ δ (2420) resonance. The π + p data at 2.85 GeV/ c indicate the onset of a dip at cos θ c.m. ≈ −0.97.
The data for cos(theta) = 1 is the extrapolation.
The data for cos(theta) = 1 and U = 0 are the extrapolations.
The data for cos(theta) = 1 and U = 0 are the extrapolations.
Backward elastic K<sup loc="post">+</sup>p and K<sup loc="post">−</sup>p scattering has been measured in the angular interval 168<sup loc="post">o</sup> <θc.m. < 177<sup loc="post">o</sup>. We find <math altimg="si1.gif">(<rm>d</rm>σ/<rm>d</rm>Ω) <inf loc="post"><rm>K</rm><sup loc="post">+</sup><rm>p</rm> → <rm>pK</rm><sup loc="post">+</sup></inf> = 17 ± 4 μ<rm>b</rm>/<rm>sr</rm></math> and <math altimg="si2.gif">(<rm>d</rm>σ/<rm>d</rm>Ω)<inf loc="post"><rm>K</rm><sup loc="post">−</sup><rm>p</rm> → <rm>pK</rm><sup loc="post">−</sup></inf> < 0.6 μ<rm>b</rm>/<rm>sr</rm></math>. K<sup loc="post">+</sup>p elastic scattering exhibits a backward peak.
The data for cos(theta) = 1 is the extrapolation.
The data for cos(theta) = 1 is the extrapolation.
We present measurements of the differential and total cross sections and the Λ polarization for the reaction K−p→ηΛ from threshold to pK−=770MeV/c, with much better precision than previous measurements. Our cross-section data show a remarkable similarity to the SU(3) flavor-related π−p→ηn cross-section results. The reaction K−p→ηΛ at threshold is dominated by formation of the intermediate Λ(1670)12− state.
Total cross section measurement for K- P --> ETA LAMBDA. Errors shown are statistical only.
Differential cross sections DSIG/DOMEGA for K- P --> ETA LAMBDA. Errors shown are statistical only.
Differential cross sections DSIG/DOMEGA for K- P --> ETA LAMBDA. Errors shown are statistical only.
The elastic scattering of 3.55 GeV/ c π + and π − mesons by protons was measured at centre-of-mass angles between 165° and 177°. The angular distributions for 864 events show a steeply rising backward peak for π + p, while the shape is less clear for π − p.
No description provided.
No description provided.
Extrapolations.