We have measured the differential cross section for π−p elastic scattering at 180° in steps of 0.10 GeV/c or less in the region P0=1.6 to 5.3 GeV/c. We detected elastic scattering events, from protons in a liquid H2 target, with a double spectrometer consisting of magnets and scintillation counters in coincidence. The incident π− beam was counted by scintillation counters. The cross section was found to have considerable structure. This may be interpreted as interference between the resonant amplitudes and the nonresonant or background amplitude. Very strong destructive interference occurs around P0=2.15 GeV/c, where the cross section drops almost two orders of magnitude in passing through the N*(2190). Another interesting feature of the data is a large narrow peak in the cross section at P0=5.12 GeV/c, providing firm evidence for the existence of a nucleon resonance with a mass of 3245±10 MeV. This N*(3245) has a full width of less than 35 MeV, which is about 1% of its mass. From this experiment we were able to determine the parity and the quantity χ(J+12) for each N* resonance, where χ is the elasticity and J is the spin of the resonance.
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Differential cross sections for the elastic scattering of negative pions from hydrogen have been measured over a limited range of squared four-momentum transfer (t) in the vicinity of t≃−3 (GeV/c)2 for incident pion momenta of 2.51, 2.76, and 3.01 GeV/c. These measurements confirm the existence of a minimum in the differential cross section in this region of incident momentum and scattering angle. The minimum occurs at a smaller value of t [t≃−2.6 (GeV/c)2] than has been observed at higher momenta.
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The elastic scattering of negative pions on protons at 2.26 GeVc has been studied using the Lawrence Radiation Laboratory 72-in. hydrogen-filled bubble chamber. The elastic scattering cross section is found to be 8.91±0.24 mb. The forward diffraction peak is well fitted by an exponential in the square of the four-momentum transfer, and the slope is found to be 8.8±0.1 GeV−2. The differential cross section is parametrized in terms of three models: optical, strong-absorption, and two-slope. It is found that the two-slope model affords the best description of the data and also does very well in predicting the polarization data of other experiments. The best-fit parameters for all three models are given. In addition, the amplitudes associated with the best fits are given for the strong-absorption and the two-slope models.
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Elastic differential cross sections were measured at 6 energies between 2.3 and 6 BeVc for π++p and π−+p. The behavior of the secondary peak as a function of energy and charge is shown. Evidence for considerable resonance structure is seen in the angular distributions.
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We report the results of the investigation of 18 500 frames of π+p interactions in the Brookhaven 20-in. bubble chamber at an incident energy of 900 MeV. It is found that single-pion production proceeds almost entirely through formation of the N33* isobar. The production mechanism of the N33* is analyzed in terms of its spin density matrix. Comparison is made with Stodolsky and Sakurai's ρ-exchange model and with the absorptive peripheral model.
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Final results are presented from a spark-chamber experiment performed at the Princeton-Pennsylvania Accelerator to measure the differential cross section near 0° for the reaction π−p→π0n. The data are extrapolated to 0° and the results of the extrapolation are compared with the results of other experiments and with dispersion relation predictions. The values of the forward-scattering amplitude for the fifteen values of incident π− momentum at which measurements were made are as follows: (p (MeV/c), (dσdΩ)0° (mb/sr)): (561,3.28), (636,2.95), (687,3.38), (750,2.48), (802,1.33), (930,2.42), (1005,3.15), (1030,3.43), (1077,1.70), (1134,1.04), (1434,0.31), (1579,0.56), (1711,0.73), (1914,0.87), (2106,0.56). The combined statistical and systematic uncertainties in these values is about ±9%. A description of the apparatus, a discussion of the methods of analysis, and a discussion of the errors contributing to the uncertainties in the above results are included in the text.
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The Berkeley 15-in. hydrogen bubble chamber was used to investigate π+−p interactions at 600 MeV. There were 1738 good events, of which 71.9±0.8% were elastic. Partial waves up to at least D52 are required to fit the elastic angular distribution. The inelastic events were almost entirely single-pion production. The ratio (p+0)(n++) was found to be 5.5±0.8 which agrees well with 4.9 predicted by the (32, 32) pion-nucleon isobar model of Olsson and Yodh. It is also consistent with 6.5 predicted by Sternheimer and Lindenbaum. The pion momentum spectra and the π−π Q-value distributions also support the Olsson and Yodh model. Thus the (32, 32) pion-nucleon isobar is apparently the principal mechanism for single-pion production at 600 MeV. Angular distributions for the single-pion-production data are presented.
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An experimental study of the elastic scattering of negative pions off protons at 2.0 GeV/ c is presented. The differential cross section is fitted to a polynomial in cos θ c.m. and the forward angular region as a diffraction peak. The results are compared with those from other bubble chamber experiments at neighbouring energies and discussed in terms of optical model and possible exchange trajectories.
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