[en] The symmetries in some interesting η meson and charge symmetry breaking processes are under observation. The relevant and crucial few body reactions are presented, with the particular attention put to determining the down-up quark mass difference. The short presentation of the state of the art of world knowledge is summarized. (author). 51 refs

[en] The ⁴He(d(pol), pα)n cross section, vector and tensor analyzing-power data with 12 and 17 MeV deuterons at kinematic conditions including proton-alpha quasifree scattering, neutron-alpha and proton-alpha final-state interactions, as well as collinearity, are compared with the predictions of the three-body model using different nucleon-alpha and neutron-proton forces. In general, better two-body potentials give a better fit to the data, except for the vector analyzing-power data. The roles of the impulse and multiple-scattering amplitudes are studied to understand the sensitivity to two-body potentials and to understand the reason for the successes and the failures of the model. 16 refs.; 6 figs.; 1 table

[en] Scintillation properties of pure CsI crystals used in the shower calorimeter being built for precise determination of the π⁺→π⁰e⁺ν_e decay rate are reported. Seventy-four individual crystals, polished and wrapped in Teflon foil, were examined in a multiwire drift chamber system specially designed for transmission cosmic muon tomography. Critical elements of the apparatus and reconstruction algorithms enabling measurement of spatial detector optical nonuniformities are described. Results are compared with a Monte Carlo simulation of the light response of an ideal detector. The deduced optical nonuniformity contributions to the FWHM energy resolution of the PIBETA CsI calorimeter for the π⁺→e⁺ν 69.8 MeV positrons and the monoenergetic 70.8 MeV photons were 2.7% and 3.7%, respectively. The upper limit of optical nonuniformity correction to the 69.8 MeV positron low-energy tail between 5 and 55 MeV was +0.2%, as opposed to the +0.3% tail contribution for the photon of the equivalent total energy. Imposing the 5 MeV calorimeter veto cut to suppress the electromagnetic losses, GEANT-evaluated positron and photon lineshape tail fractions summed over all above-threshold ADCs were found to be 2.36±0.05 (stat) ±0.20 (sys)% and 4.68±0.07 (stat)±0.20 (sys)%, respectively

[en] Recent measurements of the spin rotation parameters A and R for pion-nucleon (πN) elastic scattering and analyzing powers for πN charge exchange at 427--657 MeV/c are presented. These measurements complete a program of πN experiments in this momentum region, marking the first time that complete data sets have been obtained at any momentum for this reaction. Comparisons are made with the recent SM88 partial wave analysis from VPI and the older Karlsruhe-Helsinki and Carnegie-Mellon-Berkeley analyses

[en] A search for π⁰'s arising from the spontaneous fission of ²⁵²Cf using the LAMPF π⁰ spectrometer has yielded no evidence for this process. We obtain an upper limit of 1.4x10^-11 with a 90% confidence level for the branching ratio of π⁰'s produced at rest in the spontaneous fission of ²⁵²Cf

No abstract available

[en] The spin-rotation parameters A and R and the related spin-rotation angle β have been measured for π⁺p and π^-p elastic scattering using protons polarized in the scattering plane. The pion-beam momenta are 427, 471, 547, 625, and 657 MeV/c and the angular range is -0.9≤cosFTHETA_c.m.≤0.3. The scattered pion and recoil proton were detected in coincidence, using a scintillator hodoscope for the pions, and the Large Acceptance Spectrometer combined with the JANUS polarimeter for the recoil protons. The results are compared with the four recent πN partial wave analyses (PWA's). Our data show that the major features of these PWA's are correct. The A and R measurements complete our program of pion-nucleon experiments, providing full data sets at three of the above beam momenta. Such sets can be used to test the constraints in the PWA's or to obtain a model-independent set of πN scattering amplitudes

[en] We present new data on 2π⁰ production by 750 MeV/c π^- on hydrogen and the complex nuclei C, Al, and Cu, in search of the proposed medium modifications of the f₀(400-1200), or σ, state. We have found that the π⁰π⁰ invariant mass spectra for the four targets are different. The data indicate that nuclear absorption is mainly responsible for the change in the shape of the 2π⁰ invariant mass spectra for the complex targets. There is no hint of a narrow peak in the ππ invariant mass around 2m_π. We have also measured single π⁰ and η production on the above nuclei, in support of our investigation of nuclear final-state interaction processes. We observed strong η absorption in nuclei

[en] Precise new data for the reaction K^-p→π⁰Λ are presented in the c.m. energy range 1565 to 1600 MeV. Our analysis of these data sheds new light on claims for the Σ(1580)((3)/(2))^- resonance, which (if it exists with the specified quantum numbers) must be an exotic baryon because of its very low mass. Our results show no evidence for this state

[en] We have measured differential cross sections for pion elastic scattering from ³H and ³He in the angular region near the minimum in the non-spin-flip amplitude. Data were acquired for incident pion energies of 180, 220, 256, and 295 MeV. Nuclear charge symmetry is investigated with the aid of several charge-symmetric ratios formed from combinations of measured cross sections. A particularly intriguing result is obtained from the superratio R, which is defined as R=dσ(π⁺³H)dσ(π^-3H)/dσ(π⁺³He)dσ(π^-3He). R is found to be greater than unity at 180 MeV and significantly smaller than unity at 256 MeV, with the transition occurring at around 210 MeV. The charge-symmetry prediction for this ratio (after allowance for the Coulomb force) is one, and is independent of energy and angle. copyright 1996 The American Physical Society