The elastic scattering of 300-Mev negative pions from hydrogen was studied with the aid of a hodoscopic system with pulse-fed counters. Equation (1) gives the angular distribution for the elastic scattering under the hypothesis that the fundamental contribution to the scattering comes from the S and P waves.
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The real part of the isospin-even forward-scattering amplitude of pion-nucleon scattering has been determined at a pion energy of Tπ=55 MeV by measurement of the elastic scattering of positive and negative pions on protons within the Coulomb-nuclear interference region. The value confirms the prediction of the Karlsruhe-Helsinki phase-shift analysis for that energy. These phases have been used to determine the σ term of pion-nucleon scattering by means of dispersion relations, resulting in a value for σ which is in contradiction with chiral perturbation theory of QCD.
PI- P cross sections normalised to the Coulomb cross section taken from the Karlesruhe-Helsinki phase shift analysis (R. Koch, E. Pietarinen (NP A336(80)331).
Angular distributions of recoil-proton polarization in elastic π±p scattering were measured at 864-, 981-, and 1301-MeV incident pion kinetic energy. Polarization measurements were made by observing the azimuthal asymmetry in the subsequent scattering of recoil protons in large carbon-plate spark chambers. The spark chambers proved to be very suitable polarization analyzer detectors. Strong variation of the polarization with backward pion scattering angle was observed.
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A graphite-plate spark chamber has been used to analyze the polarization of protons recoiling from π−−p scattering. The observations were made at 90° (c.m. system) pion scattering angle for seven incident pion energies between 500 and 940 Mev, at 120° or 135° for five energies in this interval, and also at 75° for 500 Mev only. The results are compared with predictions of several models used to explain the maxima in the π−−p scattering cross section. Qualitative arguments show that the energy intervals between these maxima are not completely dominated by neighboring single-state resonances. Phase shifts found to be large in scattering also seem to be large in polarization.
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The contradiction of the σ term of pion-nucleon scattering as deduced from the Karlsruhe-Helsinki phase shifts with the smaller value calculated by the chiral perturbation theory of QCD is well known. In an effort to clarify the discrepancy we have determined the real part of the isospin-even forward-scattering amplitude of pion-nucleon scattering at a pion energy Tπ=54.3 MeV by measurement of the elastic scattering of positive and negative pions on protons in the Coulomb-nuclear interference region. The deduced value is in agreement with the prediction of the Karlsruhe-Helsinki phase-shift analysis for that energy. The resulting large value of the σ term may be interpreted as being due to the influence of s¯s sea pairs even at large distances (small Q2) as previously suggested by the European Muon Collaboration measurement of deep-inelastic scattering of polarized muons on polarized protons.
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Total and differential cross sections for π−p elastic scattering are presented at 35 energies between 1400 and 2000 MeV.
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Differential cross sections for π + p elastic scattering were measured for seven incident energies from 65 to 140 MeV at laboratory scattering angles between 93° and 165°. The results are compared with previous results of Bertin et al. and the phase-shift analysis of Arndt and Roper. Agreement between the phase-shift analysis and the data is good.
ABSOLUTE NORMALIZATION UNCERTAINTY = 2.4 PCT.
ABSOLUTE NORMALIZATION UNCERTAINTY = 2.0 PCT.
ABSOLUTE NORMALIZATION UNCERTAINTY = 1.4 PCT.
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Analyzing powers of pion-proton elastic scattering have been measured at PSI with the Low Energy Pion Spectrometer LEPS as well as a novel polarized scintillator target. Angular distributions between 40 and 120 deg (c.m.) were taken at 45.2, 51.2, 57.2, 68.5, 77.2, and 87.2 MeV incoming pion kinetic energy for pi+ p scattering, and at 67.3 and 87.2 MeV for pi- p scattering. These new measurements constitute a substantial extension of the polarization data base at low energies. Predictions from phase shift analyses are compared with the experimental results, and deviations are observed at low energies.
Analyzing power for PI+ P elastic scattering at incidient kinetic energy 87.2 MeV from the data set 1.
Analyzing power for PI+ P elastic scattering at incidient kinetic energy 68.4 MeV from the data set 1.
Analyzing power for PI+ P elastic scattering at incidient kinetic energy 57.2 MeV from the data set 1.
Elastic π+−p scattering at 1.1 Bev and elastic p−p scattering at 582 Mev have been measured using a propane bubble chamber. On the basis of 661 identified π+−p elastic scatterings found in the scanning of 1.726×106 cm of pion track, the total elastic cross section is found to be 12.3±1.2 mb. The differential cross section is rather isotropic at large angles and exhibits a strong peak for small forward scattering angles. If the forward peak is interpreted as diffraction scattering according to the optical model, the data are best fitted by a proton with a π+−p interaction radius, R=(0.99−0.11+0.13)×10−13 cm and an opacity, O=0.70−0.07+0.06. The total cross section for p−p elastic scattering at 582 Mev was found to be 24.2±1.6 mb on the basis of 2442 elastic scatterings observed in the scanning of 3.000×106 cm of proton track. Both differential and total p−p cross sections are in excellent agreement with the results of counter experiments in this energy region.
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