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In a scintillation-counter experiment, we have observed two narrow, neutral mesons in addition to the well-established η′ (958) in the reaction π−p→M0n at 2.4 GeVc. We observe a mass of 940.5 ± 1.7 MeV, Γ<10.4 MeV for the M0(940), and a mass of 962.9 ± 1.7 MeV, Γ<5.9 MeV for the δ0.
CROSS SECTION OVERALL UNCERTAINTY (APART FROM ETA PRODUCTION) ABOUT 30 PCT.
Differential cross sections have been measured for π − p elastic scattering at laboratory momenta in the range 1.2 to 3.0 GeV/ c for the c.m. range 0.97 > cos θ ∗ > −0.98 . The corresponding mass range is 1.78 to 2.56 GeV/ c 2 . The data was obtained from a counter experiment in which the scattered pions and protons were detected in coincidence by arrays of scintillation counters.
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The differential cross-section for π+ photoproduction from hydrogen by γ-rays of laboratory energy 187 MeV has been measured at four angles. Two identical counter systems, designed to detect low energy pions unambiguosly in intense electron and γ-ray backgrounds, were used in conjunction with a cylindrical liquid hydrogen target, of very low boil-off rate. The cross-sections at laboratory angles of 39.2°, 66.7°, 111.6°, and 134° are 7.49±0.47, 8.10±0.57, 8.36±0.61 and 9.54±0.61, ·10−30cm2/sr, respectively, where the assigned errors refer only to the relative values. The absolute cross-sections are in substantial agreement with the dispersion theory and confirm the front to back asymmetry.
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