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The polarization parameter in elastic π−p scattering has been measured, at the Berkeley 184-in. synchrocyclotron, with the use of a polarized proton target. At 318-, 337-, and 390-MeV incident pion kinetic energy, the angular range from 70° to 180° in the center-of-mass system was covered. At 229 MeV, polarization measurements were made in the angular range 150° to 180°. Phase-shift analyses, using these and other published data, were made at the two lowest energies.
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Differential cross sections for the reaction π−p→π0n were measured at nine incident-pion kinetic energies in the interval from 500 to 1300 MeV. The negative pion beam from the bevatron was focused on a liquidhydrogen target completely surrounded by a cubic array of six steel-plate spark chambers. The spark chambers were triggered on events with neutral final states. Charge-exchange events were identified from the one-shower and two-shower events in the spark-chamber pictures. By the Monte Carlo technique, the π0 distributions were calculated from the bisector distributions of the two-shower π0 events together with the observed γ-ray distributions of the one-shower π0 events. These π0 distributions were fitted with both Legendre-polynomial expansions and power-series expansions by the method of least squares. The extrapolated forward differential cross sections are in good agreement with the dispersion calculations. The Legendre coefficients for the differential cross sections in isospin state T=12 were obtained by combining our results with available data on π±p elastic scattering. In the light of existing phase-shift solutions, the behavior of these coefficients is discussed. The D5F5 interference term that peaks near 900 MeV is verified to be in isospin state T=12 only. We report here also the total neutral cross sections and the cross sections for the production of neutral multipion final states 2π0n and 3π0n. The 4π solid angle and the calibrated energy response of the spark chambers contribute to the accuracy of the results.
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A 14-in. liquid-hydrogen-filled bubble chamber in a 17.5-kG magnetic field was exposed to a beam of negative pions produced by the Cosmotron at Brookhaven National Laboratory. About 26 000 pictures were taken and examined for the following final states: (1) elastic scattering (π−p); (2) π+ production (π−π+n); (3) π0 production (π−π0p); (4) neutrals. Values for the cross sections for these processes are σ(elastic)=17.56±0.43 mb, σ(π+)=7.14±0.23 mb, σ(π0)=4.65±0.17 mb. The elastic-scattering angular dependence in the c.m. system is fitted by a power-series expansion in cosθ and gives the following coefficients: a0=0.27±0.02, a1=1.48±0.11, a2=3.86±0.22, a3=−0.29±0.53, a4=−0.65±0.28, a5=1.69±0.52 (units: mb/sr). Cross sections for multiple-pion production were also measured: σ(π−π+π0n)=0.33±0.04 mb, σ(π−π+π−p)=0.08±0.02 mb. The total neutral cross section was σ(neutrals)=11.78±0.43 mb; the total charged events cross section was σ(charged)=29.76±0.69 mb; and the total cross section was σ(total)=41.54±0.82 mb. For single-pion production events, two-body mass distributions and angular distributions were compared with the predictions of the Olsson-Yodh isobar model.
Axis error includes +- 0.0/0.0 contribution (?////STATISTICAL YIELD DOMINATES).
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Total cross sections for negative pions on protons were measured at laboratory energies of 230, 290, 370, 427, and 460 Mev. The measurements were made in the same pion beams as and at energies identical with those of our π−−p differential scattering experiments. Comparisons of the total and differential scattering can be made with the dispersion theory at a given energy without introducing the systematic errors that would normally enter due to uncertainties in the parameters of more than one pion beam. The measured total cross sections are found to agree within statistics with other measured values, and with the sums of elastic, inelastic, and charge-exchange cross sections measured at this laboratory. The results are:
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The differential cross section for charge-exchange scattering of negative pions by hydrogen has been observed at 230, 260, 290, 317, and 371 Mev. The reaction was observed by detecting one gamma ray from the π0 decay with a scintillation-counter telescope. A least-squares analysis was performed to fit the observations to the function dσdω=Σl=15alPl−1(cosθ) in the c.m. frame. The best fit to our experimental measurements requires only s- and p-wave scattering. The results (in mb) are: The least-squares analysis indicates that d-wave scattering is not established in this energy range.
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