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Differential cross sections for the elastic scattering of positive pi mesons by protons were measured at the Berkeley Bevatron at pion laboratory kinetic energies between 500 and 1600 MeV. Fifty scintillation counters and a matrix coincidence system were used to identify incoming pions and detect the recoil proton and pion companions. Results were fitted with a power series in the cosine of the center-of-mass scattering angle, and total elastic cross sections were obtained by integrating under the fitted curves. The coefficients of the cosine series are displayed, plotted versus the laboratory kinetic energy of the pion. The most striking features of these curves are the large positive value of the coefficient of cos6θ*, and the large negative value of the coefficient of cos4θ*, both of which maximize in the vicinity of the 1350-MeV peak in the total cross section. These results indicate that the most predominant state contributing to the scattering at the 1350-MeV peak has total angular momentum J=72, since the coefficients for terms above cos6θ* are negligible at this energy. One possible explanation is that the 1350-MeV peak is the result of an F72 resonance lying on the same Regge-pole trajectory as the (32, 32) resonance near 195 MeV.
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Differential cross sections for elastic π−p scattering were measured at eight energies for positive pions and seven energies for negative pions. Energies ranged from 310 to 650 MeV. These measurements were made at the 3-GeV proton synchrotron at Saclay, France. A beam of pions from an internal BeO target was directed into a liquid-hydrogen target. Fifty-one scintillation counters and a matrix-coincidence system were used to measure simultaneously elastic events at 21 angles and charged inelastic events at 78 π−p angle pairs. Events were detected by coincidence of pulses indicating the presence of an incident pion, scattered pion, and recoil proton, and the results were stored in the memory of a pulse-height analyzer. Various corrections were applied to the data and a least-squares fit was made to the results at each energy. The form of the fitting function was a power series in the cosine of the center-of-mass angle of the scattered pion. Integration under the fitted curves gave values for the total elastic cross sections (without charge exchange). The importance of certain angular-momentum states is discussed. The π−−p data are consistent with a D13 resonant state at 600 MeV, but do not necessarily require such a resonant state.
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The Fermilab hybrid 30-in. bubble-chamber spectrometer was exposed to a tagged 147-GeV/c positive beam containing π+, K+, and p. A sample of 3003 K+p, 19410 pp, and 20745 π+p interactions is used to derive σn, 〈n〉, f2cc, and 〈nc〉D for each beam particle. These values are compared to values obtained at other, mostly lower, beam momenta. The overall dependence of 〈n〉 on Ea, the available center-of-mass energy, for these three reactions as well as π−p and pp interactions has been determined.
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New high-statistics measurements of π + p elastic scattering differential cross sections are presented at 30 momentum points between 1.282 and 2.472 GeV/ c , covering most of the angular distribution outside the forward diffractive peak. These data show significant disagreements at some momenta with previous high-statistics experiments and with current partial wave analyses.
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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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A simple, large-solid-angle apparatus, specially suited for the measurement of backward elastic scattering of medium-energy pions on protons and deuterons, is described. The method of analysis which reduces background and determines elastic events from a data sample of 185 MeV negative pions incident on a D 2 O target is discussed. Results for 141 MeV π + p and 185 MeV π − p backward cross-sections are also presented and compared with cross-sections calculated from known phase shifts.
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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).
Results are presented on π + p and K + p elastic scattering at 250 GeV/ c , the highest momentum so far reached for positive meson beams. The experiment (NA22) was performed with the european hybrid spectrometer. The π + p elastic cross section stays constant with energy while the K + p cross section increases.
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ERRORS IN ELASTIC CROSS SECTIONS INCLUDE SYSTEMATIC ERRORS.