[en] The author reports on a recent search for bar ν_e appearance from stopped π⁺ → μ⁺ν_μ and μ⁺ → e⁺ν_e bar ν_μ decay made by the LAMPF experiment E645. The appearance of bar ν_e may occur from bar ν_μ → bar ν_e, ν_e → bar ν_eL, or ν_μ → bar ν_eL oscillations. Appearance may also occur from rare μ⁺ → e⁺bar ν_eν_μ decay, which is allowed by a multiplicative lepton charge conservation law. The neutrino energies range from E_ν = 0 to 52.8MeV. The neutrino detector, which is located 26.1 meters from the neutrino source, consists of a segmented liquid scintillator and proportional drift tube central detector surrounded by both active and passive shielding. The central detector detects bar ν_e through the bar ν_ep → ne⁺ Charge Current (CC) reaction, which is signaled by the direct detection of the final state positron and neutron. The hydrogen-rich liquid scintillators act as free proton targets for the bar ν_ep CC reaction. The neutrons are detected through radiative neutron capture on gadolinium. He finds no evidence for bar ν_e appearance in the first year of running. New limits on the bar ν_μ, ν_e, ν_μ yields bar ν_e oscillation parameters and the rare μ⁺ → e⁺bar ν_eν_μ decay branching ratio are presented

[en] The authors report the recent progress on laser manipulation of the short-lived (22 sec half-life) radioactive ²¹Na atoms. Since they successfully demonstrated laser trapping of short-lived radioactive isotope at LBL's 88 inch Cyclotron, the authors have made substantial improvements in their experimental apparatus. Using a new high temperature oven and MgO target, the thermal atomic beam of ²¹Na has been greatly increased. A new trapping magnet has been fabricated, which promises higher trapping efficiency. Currently they are working on the precise measurement of the hyperfine structure of the ²¹Na and new laser trapping schemes which provide polarized trapped atoms. These techniques will lead to a precision measurement of the decay asymmetry parameter, which is a sensitive test of the V-A structure of the weak charged current

[en] The weak vector coupling constant of the nucleon is a fundamental parameter of the Standard Model of Electro-Weak Interactions. Its most precise determination comes from nuclear physics experiments, in particular, from measurements of 0⁺ → 0⁺ superallowed beta decays. Precise knowledge of this parameter will allow a variety of tests of the Standard Model, in addition to forcing a number of important constraints on astrophysics and cosmology. Determination of the vector coupling constant requires precision nuclear physics measurements along with state of the art theoretical nuclear physics calculations. Such measurements and calculations have been made for a variety of nuclei ranging from ¹⁴O to ⁵⁴Co. Although the vector coupling constant obtained from these experiments are statistically independent of nuclear charge Z, the average value obtained implies a non-unitary Cabibbo-Lobayashi-Maskawa quark mixing matrix, which if correct, would require exotic extensions to the Standard Model. Unfortunately the theoretical uncertainties are great and controversial. For example the isospin breaking correction predicted by two independent groups differ significantly. In order to solve this controversy, there have been much recent effort to measure the vector coupling constant from the superallowed decay of ¹⁰C, where the theoretical corrections are expected to be less siginficant. This is a very challenging experiment, since it requires the precision measurement of very small branching ratios in a high background environment. The author describes the current status of the determination of the weak vector coupling constant emphasizing the recent experimental effort to measure the vector coupling constant from the superallowed decay of ¹⁰C

[en] The vector coupling constant is a fundamental parameter of the Standard Model of Electo-Weak Interactions. Its most precise determination comes from nuclear physics experiments, in particular, from measurements of 0⁺→0⁺ superallowed β decays. I will describe two measurements of the vector coupling constant from the superallowed decay of ¹⁰C that are currently in progress. copyright 1995 American Institute of Physics

[en] We have measured the branching ratio to the super-allowed Fermi transition in ¹⁰C beta decay, ¹⁰C(0⁺, g. s.)→¹⁰B(0⁺,1.74MeV)+e⁺ +ν. Results of this measurement will be presented. Precise knowledge of this branching ratio is needed to compute the partial experimental Fermi ft-value and the weak vector coupling constant

[en] We report on a recent search for bar ν_e appearance from stopped π⁺ → μ⁺ν_μ and μ⁺ → e⁺ν_e bar ν_μ decay made by the LAMPF experiment E645. The appearance of bar ν_e may occur from bar ν_μ → bar ν_e, ν_e → bar ν_eL, or ν_μ → bar ν_eL oscillations. Appearance may also occur from rare μ⁺ → e⁺bar ν_eν_μ decay, which is allowed by a multiplicative lepton charge conservation law. The neutrino energies range from E_ν = 0 to 52.8MeV. The neutrino detector, which is located 26.1 meters from the neutrino source, consists of a segmented liquid scintillator and proportional drift tube central detector surrounded by both active and passive shielding. The central detector detects bar ν_e through the bar ν_ep → ne⁺ Charge Current (CC) reaction, which is signaled by the direct detection of the final state positron and neutron. The hydrogen-rich liquid scintillators act as free proton targets for the bar ν_ep CC reaction. The neutrons are detected through radiative neutron capture on gadolinium. We find no evidence for bar ν_e appearance in the first year of running. New limits on the bar ν_μ,ν_e,ν_μ → bar ν_e oscillation parameters and the rare μ⁺ → e⁺bar ν_eν_μ decay branching ratio are presented. 87 refs., 45 figs., 17 tabs

[en] We report the recent development on laser manipulation of radioactive ²¹Na atoms. With 25 Mev proton beam from 88 inches. Cyclotron, we have routinely produced a thermal atomic beam of 10⁷²¹Na atoms/sec, via the ²⁴Mg(p,α)²¹Na reaction. The collimation of this radioactive beam by the laser has been demonstrated. The very important ingredients for trapping radioactive atoms will be addressed. An optimized scheme is being developed to provide both high capture efficiency and trap stability. This will enable us to laser trap ²¹N a based on our current ²¹Na beam. The trapped ²¹N a will provide precision beta decay asymmetry measurement to test the V-A structure of the charged current

[en] The beta-neutrino correlation coefficient, a_βν, in Na²¹ is inferred from detecting the β⁺ and low-energy recoil daughter nucleus. Na²¹ is produced at the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory and 800 000 atoms are maintained in a magneto-optical trap. From the measured time of flight of recoil ions in the presence of a drift electric field, we find a_βν=0.5243±0.0091. There may be a dependence on the trapped atom population. This and other systematic uncertainties are discussed

[en] We have searched for the effect of a neutrino of mass 17 keV/c² in the beta decay of ³⁵S with an apparatus incorporating a high resolution solid state detector and a super conducting solenoid. The experimental mixing probability of the 17keV neutrino is consistent with zero. The experimental sensitivity is verified by measurements with a mixed source of ³⁵S and ¹⁴C, which artificially produces a distortion in the beta spectrum similar to that expected from the massive neutrino. Recently, we have performed similar searches in the beta decay of ¹⁴C and ⁶³Ni. Results of these new measurements will be presented

[en] Higher order beta decay matrix elements, such as weak magnetism, will introduce small departures (a shape factor) from the allowed beta decay electron energy spectrum. The value of the weak magnetism matrix element is predicted by the Conserved Vector Current (CVC) hypothesis and an experimental determination of the weak magnetism matrix element can be interpreted as a test of CVC. We have determined the weak magnetism matrix element from the ¹⁴C shape factor, which was measured using an apparatus incorporating a high resolution solid state detector and a super conducting solenoid. The results of our measurement will be presented