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.
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The pure QED reaction e + e − → γγ has been studied at centre of mass energies around the mass of the Z 0 boson using data recorded by the OPAL detector at LEP. The results are in good agreement with the QED prediction. Lower limits on the cutoff parameters of the modified electron propagator are found to be Λ + >89 GeV and Λ. The lower limit on the mass of an excited electron is 82 GeV assuming the coupling constant λ =1. Upper limits on the branching ratios of Z 0 → γγ , Z 0 → π 0 γ and Z 0 → ηγ are set at 3.7×10 −4 , 3.9×10 −4 and 5.8×10 −4 respectively. Two events from the reaction e + e − → γγγ have been observed, consistent with the QED prediction. An upper limit on the branching ratio of Z 0 → γγγ is set at 2.8×10 −4 . All the limits are given at 95% confidence level.
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Data read from graph.
The absolute p-d elastic-scattering differential cross sections were measured at 641.3 and 792.7 MeV beam energies over a range of c.m. angles from ∼35° to ∼115° and ∼35° to ∼140°, respectively. The longitudinally polarized (L-type) proton beam produced by the Lamb-shift ion source at LAMPF was used. The beam intensity was measured to high accuracy (∼0.1%) by a scintillator-beam particle-counting system designed and developed prior to the experiment. Typical uncertainties in the absolute cross sections were about 2–3% total, somewhat larger at back angles. The present results were compared with the existing measurements and the controversy about the previous data at 800 MeV was resolved. The present data can be fit with a relativistic multiple-scattering theory which uses off-mass-shell extrapolations of the nucleon-nucleon amplitudes suggested by the structure of derivative meson-nucleon couplings. Relativistic-impulse-approximation calculations do not fit these data at either energy.
TARGET IS A LIQUID DEUTERIUM. THE LABORATORY ANGLES BIN SIZES ARE 30 MRAD AT FORWARD ANGLES AND 50 MRAD AT OTHER ANGLES.
TARGET IS A LIQUID DEUTERIUM. THE DATA IN THIS TABLE ARE THE SAME AS IN THE TABLE 1, BUT IN THE ANOTHER REPRESENTATION.
TARGET IS A LIQUID DEUTERIUM. THE DATA IN THIS TABLE ARE THE SAME AS IN THE TABLE 1, BUT IN THE ANOTHER REPRESENTATION.
Absolute pp-elastic-differential cross sections were measured at incident energies 492, 576, 642, 728, and 793 MeV from about 30° to 90° c.m. The total uncertainty was determined to be less than 1%, made possible by particle counting for beam normalization and extensive cross-checks of systematic effects. These new data are consistent with previous data above 600 MeV but have uncertainties about a factor of 10 smaller. Near 500 MeV these data are consistent with 90° data from TRIUMF, but differ significantly from similar data from PSI; the cause of this discrepancy is discussed.
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pp-elastic differential cross sections are reported at 492 MeV from 40° to 90°, and at 576, 642, 728, and 793 MeV from 75° to 90° c.m., with an absolute accuracy of less than 1%. These data, obtained with polyethylene targets, agree with recent measurements at the same energies obtained with a liquid-hydrogen target. © 1996 The American Physical Society.
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In this paper we report measurements of the backward K−p differential cross section at 49 momenta covering the momentum range 476-1084 MeV/c. The statistical precision achieved, typically 2.5%, is an order of magnitude better than previous measurements. The systematic errors for this reaction are about 1%. The differential cross section for the reaction K−p→Σ−π+ where the π+ emerges at 0° has also been measured at 32 momenta with comparable improvement in precision over previous experiments. A partial-wave analysis of the K¯N channels including the new K−p backward elastic data is presented.
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Differential cross sections have been measured for π − p elastic scattering at laboratory momenta in the range 1.2 to 3.0 GeV/ c for the c.m. range 0.97 > cos θ ∗ > −0.98 . The corresponding mass range is 1.78 to 2.56 GeV/ c 2 . The data was obtained from a counter experiment in which the scattered pions and protons were detected in coincidence by arrays of scintillation counters.
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Cross sections for elastic Compton scattering from the deuteron were measured over the laboratory angles 35-150 deg. Tagged photons in the laboratory energy range 84-105 MeV were scattered from liquid deuterium and detected in the large-volume Boston University NaI (BUNI) spectrometer. Using the calculations of Levchuk and L'vov, along with the measured differential cross sections, the isospin-averaged nucleon polarizabilities in the deuteron were estimated. A best-fit value of (alpha-beta) = 2.6+/-1.8 was determined, constrained by dispersion sum rules. This is markedly different from the accepted value for the proton of (alpha-beta) = 10.0+/-1.5+/-0.9.
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Neutron polarizability is evaluated from the deuteron data.
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The cross section for 180° elastic scattering of antiprotons by protons between 406 and 922 MeV/c has been measured. A single-arm spectrometer detected recoil protons corresponding to events with 〈cosθc.m.〉=−0.994. The regions of the reported resonances at 1936 and 2020 MeV were scanned in 10-MeV/c steps with a typical statistical error of ≈ 7% and an rms mass resolution of ±3 MeV. No narrow enhancements (Γ<10 MeV) were observed.
735 MEV/C VALUE MISPRINTED IN JOURNAL - CORRECTION SUPPLIED BY M. A. GARNJOST (PRIV COMM 28 MAR 1980).
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