The total and differential cross-sections for the reaction e + e − → γγ ( γ ) are measured at centre of mass energies around 91 GeV using an integrated luminosity of 4.7 pb −1 . The aggreement with QED prediction is good. Consequently there is no evidence for non-standard channels which would have the same experimental signature. The lower limits on the QED cuttoff parameters are Λ + > 113 GeV and Λ − > 95 GeV. An upper limit on the effective coupling between a possible excited electron and the gamma is derived. At 95% confidence level the branching ratios for Z 0 decay into π 0 γ, ηψ and γγγ are below 1.5 × 10 −4 , 2.8 × 10 −4 and 1.4 × 10 −4 respectively.
Radiative effects are subtracted.
Radiative effects subtracted.
Absolute π±d differential cross sections and charge asymmetries have been measured at an incident pion energy of 65 MeV, using an active target of deuterated scintillator plastic to detect recoil deuterons in coincidence with scattered pions. Statistical and systematic uncertainties in the cross sections are each typically ±3%. The charge asymmetry is consistent with theoretical predictions.
No description provided.
Differential cross sections for the reactions γp→π0p, π+n and γn→π−p, π0n were measured in a single experiment using tagged photons in the energy region 240-450 MeV incident on H21 and H22 targets. Results of the measurements of the ratios π0nπ0p and π−pπ+n are presented. The ratio of isotensor to isovector amplitude is found to be 0.00±0.02.
No description provided.
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Based on 150 000 photographs taken at the ZGS with the 30 inch deuterium-filled chamber we present an analysis of the elastic p d scattering reaction. Due to unrecoreded small deuteron recoils we were only able to measure the elastic cross section in the four-momentum region | t | > 0.03 (GeV/ c ) 2 . Extrapolation towards small | t | by two different methods gave us two compatible estimates of the total elastic cross section. The differential cross section was analyzed by means of the Glauber formalism both with and without the effects due to the D-wave part of the deuteron wave function. The differential cross sections of np at 5.4 GeV/ c and pn deduced from our data were compared and exhibit a crossover phenomenon.
CALCULATED USING TOTAL ELASTIC SIG(-T > 0.03 GEV**2) = 7.2 +- 0.4. THE SMALL ANGLE SCATTERING APPROXIMATION HOLDS: D(SIG)/DOMEGA(RF=LAB) = (P**2/PI)*D(SIG)/DT.
INTEGRATED CROSS SECTION USING EITHER EXPONENTIAL EXTRAPOLATION OR GLAUBER MODEL FIT FOR -T < 0.03 GEV**2.
Interactions of 683-MeV/c negative pions with protons were investigated using the BNL 14-in. hydrogen bubble chamber in a 17-kG field. Two thousand elastic scatterings were analyzed, yielding a cross section of 18.9±1.0 mb. No evidence for powers of cosθ higher than the second was observed in the elastic angular distribution. The angular distribution obtained was dσdω=(0.384±0.026)+(1.70±0.06)cosθ+(3.36±0.11)cos2θ mb/sr. The single-pion production reactions π−+p→π−+π0+p and π−+p→π−+π++n were studied in detail. A total of 441 π0 productions and 833 π+ productions were analyzed giving cross sections of 3.99±0.50 and 7.50±0.80 mb, respectively. The differential distributions for these inelastic processes are presented and compared with the predictions of the model of Olsson and Yodh. The distribution of events on the Dalitz plots for π0 production is accounted for by the model. However, for the π+ reaction, the model (so far developed) does not describe adequately the distribution of events on the Dalitz plot. In particular, the model fails to account for the enhancement at high (π+π−) effective masses in ππ mass distribution. The center-of-mass angular distributions for π0 and π+ production reactions are presented and compared with the model.
No description provided.
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