Measurements of π±p elastic differential cross-sections have been performed in the forward direction, using a missing-mass spark chamber spectrometer. The films have been seanned by an automatic apparatus. A phase-shift analysis of the experimental data has been done, leading to three solutions. Various experiments are proposed in order to resolve the ambiguities.
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The differential cross section for π±−p elastic scattering at 180° was measured from 0.572 to 1.628 GeVc using a double-arm scintillation-counter spectrometer with an angular acceptance θ* in the center-of-mass system defined by −1.00≤cosθ*≤−0.9992. The π+−p cross section exhibits a large dip at 0.737 GeVc and a broad peak centered near 1.31 GeVc. The π−−p cross section exhibits peaks at 0.69, 0.97, and 1.43 GeVc.
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The π + p cross section for elastic scattering from hydrogen was measured at seven incident energies ranging from 20.8 to 95.9 MeV for an angular range from 60° to 145°. The experimental set-up is discussed in detail as well as the method used for data analysis. A table of results and a set of phase shifts are provided.
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The energy dependence of the differential cross section for $\pi^+ p$ elastic scattering at a c.m. angle near 174 ° has been measured. The momentum range of incident $\pi^+$ was 2.06-4.70 GeV/c. On this energy dependence one can see a structure, i.e. maxima corresponding to the baryon resonances $\Delta(2420)$ and $\Delta(2840)$. The structure is used for determination of the parities of these resonances.
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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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The backward angular distributions obtained in an experiment at the Zero Gradient Synchrotron of Argonne National Laboratory were used to systematically study the energy dependence of the 180° differential cross section for π+p elastic scattering in the center-of-mass energy region from 2159 to 3487 MeV. At each of 38 incident pion momenta between 2.0 and 6.0 GeV/c, a focusing spectrometer and scintillation counter hodoscopes were used to obtain differential cross sections for typically five pion scattering angles from 141° to 173° in the laboratory. Values for dσdΩ at 180° were then obtained by extrapolation. A resonance model and an interference model were used to perform fits to the energy dependence of dσdΩ (180°). Both models led to good fits to our data and yielded values for the masses, widths, parities, and the product of spin and elasticity for the Δ(2200), Δ(2420), Δ(2850), and Δ(3230) resonances. Our data confirm the existence of the Δ(3230) and require the negative-parity Δ(2200).
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Differential cross sections are presented for pion-proton elastic scattering in the angular range −0.6≳cosθc.m.≳−0.98 at 15 incident π+ momenta from 2.18−5.25 GeVc. The angular distributions rise steeply near 180° at all momenta. For laboratory momenta ≳2.75 GeVc they show a minimum at u≈−0.17 (GeVc)2 and a broad maximum near u≈−0.6 (GeVc)2. When the data are plotted versus s, for fixed u, a strong signal from the Δ(2420) resonance is observed. The data are compared with a direct-channel resonance model and with a Regge model which considers the exchange of the Nα, Nγ, and Δδ Regge trajectories. The qualitative success of both the direct-channel resonance model and the Regge model lends support to the concept of duality.
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The angular distribution π+-p at 1.0 GeV was determined on the basis of l032 events measured in a propane bubble chamber. Comparison is made with data of 820 and 900 MeV and with angular distributions π−+p at similar energies.
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