Results of systematic measurements of the asymmetry parameter in the elastic scattering of pions on polarized protons at 1.4–2.1 GeV/ c in the backward hemisphere are presented together with a test of the isospin invariance of the data set available on pion-proton scattering in the investigated momentum range. The transversity isodoublet amplitudes at 1.98 and 2.07 GeV/ c are reconstructed. The obtained data, the isospin analysis and amplitude reconstruction results are compared with the current phase-shift analysis predictions.
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NAME=THEORY DENOTES THE MONTE-CARLO GENERATED CROSS SECTIONS.
The asymmetry in the scattering of π− mesons by polarized protons has been measured at 50 different momenta from 0.643 to 2.14 GeV/c. Results were obtained at values of cosθ ranging from approximately +0.9 to -0.95 in the c.m. system at each incident pion momentum. The pion beam was incident on a 7.6-cm-long crystal assembly of lanthanum magnesium nitrate, in which the hydrogen in the water of crystallization was polarized by the "solid effect." The total momentum spread of the beam was 10% (full width at half-height) and data were collected simultaneously in 4 momentum channels, each with 2½% full width at half-height. A gas Čherenkov counter was used to reject incoming electrons. Scattered particles were detected in scintillation counter arrays placed within the 10-cm gap of the polarized target magnet. Encoded information from each array was stored in the memory of a PDP-5 computer connected on-line to a fast electronic logic network. The computer was programmed to classify the events according to momentum and scattering angle and subdivide them into coplanar and noncoplanar categories. The latter provided a measure of the background. The results have been expressed in the form of an expansion in terms of first associated Legendre polynomial series and compared with the predictions of recent phase-shift solutions. It is concluded that although these analyses give satisfactory predictions of the general features of the results, no one solution gives complete agreement with the data above about 1.0 GeV/c.
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Measurements are reported of the difference ΔσL between proton-proton total cross sections for parallel and antiparallel spin states and of the parameter CLL for proton-proton elastic scattering near 90°, for thirteen energies between 300 and 800 MeV. The ΔσL results agree well with previous ANL ZGS and SIN data, but disagree with recent results from TRIUMF. Attempts to understand the cause of the discrepancy have been unsuccessful, but possible sources are discussed. The ΔσL and CLL results have been used with other experimental data to extract quantities which depend only on spin-singlet, coupled spin-triplet, and spin-triplet partial waves. Structure is found in these quantities, which appears to be associated with the resonantlike D21 and F33 partial waves. Additional similar structure is also found, which may be due either to the P03 partial wave or the (P23,F23) partial-wave pair.
ERRORS ARE STATISTICAL ONLY. THERE IS ADDITION OF 2.0 AND 2.1 PCT SYSTEMATICS.
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The absolute differential cross section for proton-proton elastic scattering has been measured at 90° c.m. for 300, 350, 400, 450 and 500 MeV. The statistical uncertainty of the measurements is 0.5% with an additional systematic normalization uncertainty of 1.8%. The results are compared to phase-shift analyses.
The statistical and systematic errors are added in quadrature.
Measurements of C LL of pp elastic scattering near θ c.m. = 90° at thirteen energies between 300 and 800 MeV are reported. These, together with previous values of C NN , are used to extract values of two quantities, ƒ s and ƒ t , which contain only spin-singlet and only coupled spin-triplet partial waves, respectively. The ƒ s curve, which is not dependent on C LL , exhibits the behavior expected for the previously conjectured 1 D 2 resonance. The ƒ t curve also exhibits a resonance-like behavior, which could be due either to the 3 P 0 or the 3 P 2 partial wave.
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The pp total, elastic, and all the inelastic cross sections were measured at 11 momenta in the range 0.9–2.0 GeV/c. No clear structure was observed in their momentum dependences. The momentum dependence of the total cross section agrees quite well with the result of a phase-shift analysis by Arndt. Our measurement of the ppπ 0 and pnπ + cross sections served to normalize the earlier systematic but relative and extrapolated measurements of these cross sections over a narrower momentum range. Calculations by König and Kroll based on a pion exchange model including the effect of an I = 1 dibaryon did not fit the single-pion production cross sections.
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The absolute normalisation of the polarisation in pp elastic scattering at 24 degrees lab has been determined by means of a double-scattering experiment to an accuracy of +or-1.5% at five energies between 200 and 520 MeV.
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The parameters D, R, R' and P for pp elastic scattering have been measured in the centre-of-mass angular range 13 degrees to 58 degrees with an accuracy of about +or-0.02 at 209, 324, 379, 425 and 515 MeV. These results are incorporated with earlier data into a phase-shift analysis. Phase-shifts are generally in agreement with the theoretical predictions of the Paris group, although the F-wave spin-orbit combination is rather stronger than predicted. The fitted value for the pi 0pp coupling constant in g02=14.06+or-0.65.
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