R. S. Kessler

The η-meson mass

Abstract The mass of the η meson has been measured through the study of the d p→ 3 He η reaction near threshold, the beam having been calibrated through comparison with three other nuclear reactions. The value obtained is m η =547.30±0.15 MeV/ c 2 , where the error bar includes both systematic and statistical effects. This is much more precise and significantly lower than the Particle Data Group average, through it is consistent with a previous counter experiment.

Calibration of neutron counters from 83 to 290 MeV

The eight neutron detectors described in the preceding paper have been calibrated with tagged neutrons from the reaction π−d → nn for Tn = 83–290 MeV. The neutron detection coefficient λ is (8.7 ± 0.2) × 10−3/(cm path length) at 83 MeV and decreases monotonically to (7.6 ± 0.5) × 10−3/(cm path length) at 290 MeV. Measurements were made repeatedly for different configurations to show the internal consistency of the data. Our results are in good agreement with the calibration data for neutron counters reported by Betti et al. but not with the work of Strong et al. Our data support the energy dependence of the efficiencies calculated by the Kent State University neutron efficiency code.

Reactions {ital pd}{r_arrow}{sup 3}He{eta} and {ital pd}{r_arrow}{sup 3}He{pi}{sup +}{pi}{sup {minus}} near the {eta} threshold

The reaction {ital pd}{r_arrow}{sup 3}He{eta} has been studied with the SPES2 spectrometer, for proton energies between 0.2 MeV and 11 MeV above threshold. The total cross section rises from 0.25 to 0.40 {mu}b in this region. The observed energy dependence can be attributed to the strong final state interaction. The angular distribution is nearly isotropic, consistent with {ital S} wave production. A measurement of the {ital pd}{r_arrow}{sup 3}He{pi}{sup +}{pi}{sup {minus}} cross section in the threshold region is also presented. The setup, which is capable of producing 10{sup 5} tagged {eta}/s with only a few percent background, is used to investigate rare {eta} decays. {copyright} {ital 1996 The American Physical Society.}

The Reactions p d ---> He-3 eta and p d ---> He-3 pi+ pi- near the eta threshold

The reaction {ital pd}{r_arrow}{sup 3}He{eta} has been studied with the SPES2 spectrometer, for proton energies between 0.2 MeV and 11 MeV above threshold. The total cross section rises from 0.25 to 0.40 {mu}b in this region. The observed energy dependence can be attributed to the strong final state interaction. The angular distribution is nearly isotropic, consistent with {ital S} wave production. A measurement of the {ital pd}{r_arrow}{sup 3}He{pi}{sup +}{pi}{sup {minus}} cross section in the threshold region is also presented. The setup, which is capable of producing 10{sup 5} tagged {eta}/s with only a few percent background, is used to investigate rare {eta} decays. {copyright} {ital 1996 The American Physical Society.}

Comparison of (π−d→nn withdσ(π+d→pp) to test charge symmetry in the Δ-region

First results on π−d → are reported. The measurements were made using 8 specially designed neutron counters, which were carefully calibratedin situ. The differential cross sections atTπ=142, 180, 217, and 254 MeV were obtained at four angles between 0° and 90°, they are compared to π+d →pp data measured at the same energies and angles with the same setup. At every beam energy, the shape of the angular distributions of π−d →nn and π+d →pp is the same to ±2%. The absolute cross sections differ by 1 to 10%. The error in this comparison is ±4% implying a small violation of charge symmetry.