[en] For the on-line production of a ¹⁴O⁺ ion beam, an integrated target-transfer line ion source system is now under development at LBNL. ¹⁴O is produced in the form of CO in a high temperature carbon target using a 20 MeV ³He beam from the LBNL 88'' Cyclotron via the reaction ¹²C(³He,n)¹⁴O. The neutral radioactive CO molecules diffuse through an 8 m room temperature stainless steel line from the target chamber into a cusp ion source. The molecules are dissociated, ionized and extracted at energies of 20 to 30 keV and mass separated with a double focusing bending magnet. The different components of the setup are described. The release and transport efficiency for the CO molecules from the target through the transfer line was measured for various target temperatures. The ion beam transport efficiencies and the off-line ion source efficiencies for Ar, O₂ and CO are presented. Ionization efficiencies of 28% for Ar⁺, 1% for CO, 0.7% for O⁺, 0.33 for C⁺ have been measured

[en] The β-ν correlation coefficient, a_βν, is measured in ²¹Na by detecting the time of flight of the recoil nucleus detected in coincidence with the atomic electrons shaken off in β decay. The sample of ²¹Na is confined in a magneto-optic trap. High detection efficiency allows low trap density, which suppresses the photoassociation of molecular sodium, which can cause a large systematic error. Suppressing the fraction of trapped atoms in the excited state by using a dark trap also reduces the photoassociation process, and data taken with this technique are consistent. The main remaining systematic uncertainties come from the measurement of the position and size of the atom trap and the subtraction of background. We find a_βν=0.5502(60), in agreement with the Standard Model prediction of a_βν=0.553(2), and disagreeing with a previous measurement, which was susceptible to an error introduced by the presence of molecular sodium

[en] The charge-state distribution following the β⁺ decay of²¹Na has been measured, showing a larger than expected fraction of the daughter ²¹Ne in positive charge states. No dependence on either the β⁺ or recoil nucleus energy is observed. The data are compared to a simple model based on the sudden approximation. Calculations suggest that a small but important contribution from recoil ionization has significant consequences for precision β decay correlation experiments detecting recoil ions

[en] We have measured the half-life of ¹⁴O, a superallowed (0⁺→0⁺) β decay isotope. The ¹⁴O was produced by the ¹²C(³He,n)¹⁴O reaction using a carbon aerogel target. A low-energy ion beam of ¹⁴O was mass separated and implanted in a thin beryllium foil. The beta particles were counted with plastic scintillator detectors. We find t_1/2=70.696±0.052 s. This result is 1.5σ higher than an average value from six earlier experiments, but agrees more closely with the most recent previous measurement

[en] We report on an experimental and theoretical study of the dynamic (ac) Stark effect on a forbidden transition. A general framework for parametrizing and describing off-resonant ac-Stark shifts is presented. A model is developed to calculate spectral line shapes resulting from resonant excitation of atoms in an intense standing light wave in the presence of off-resonant ac-Stark shifts. The model is used in the analysis and interpretation of a measurement of the ac-Stark shifts of the static-electric-field-induced 6s²¹S₀→5d6s³D₁ transition at 408 nm in atomic Yb. The results are in agreement with estimates of the ac-Stark shift of the transition under the assumption that the shift is dominated by that of the 6s²¹S₀ ground state. A detailed description of the experiment and analysis is presented. A biproduct of this work is an independent determination (from the saturation behavior of the 408-nm transition) of the Stark transition polarizability, which is found to be in agreement with our earlier measurement. This work is part of the ongoing effort aimed at a precision measurement of atomic parity-violation effects in Yb

[en] High precision fundamental neutron physics experiments have been proposed for the intense pulsed spallation neutron beams at JSNS, LANSCE, and SNS to test the standard model and search for new physics. Certain systematic effects in some of these experiments have to be controlled at the few ppb level. The NPD Gamma experiment, a search for the small parity-violating γ-ray asymmetry A_Y in polarized cold neutron capture on parahydrogen, is one example. For the NPD Gamma experiment we developed a radio-frequency resonant spin rotator to reverse the neutron polarization in a 9.5 cm x 9.5 cm pulsed cold neutron beam with high efficiency over a broad cold neutron energy range. The effect of the spin reversal by the rotator on the neutron beam phase space is compared qualitatively to rf neutron spin flippers based on adiabatic fast passage. We discuss the design of the spin rotator and describe two types of transmission-based neutron spin-flip efficiency measurements where the neutron beam was both polarized and analyzed by optically polarized ³He neutron spin filters. The efficiency of the spin rotator was measured at LANSCE to be 98.8 ± 0.5% for neutron energies from 3 to 20 meV over the full phase space of the beam. Systematic effects that the rf spin rotator introduces to the NPD Gamma experiment are considered

[en] We have measured the triple correlation D< J_n>/J_n·(β_e x p-hat_ν) with a polarized cold-neutron beam (Mumm et al., Phys Rev Lett 107:102301, 2011; Chupp et al., Phys Rev C 86:035505, 2012). A non-zero value of D can arise due to parity-even-time-reversal-odd interactions that imply CP violation. Final-state effects also contribute to D at the level of 10^− 5 and can be calculated with precision of 1 % or better. The D coefficient is uniquely sensitive to the imaginary part of the ratio of axial-vector and vector beta-decay amplitudes as well as to scalar and tensor interactions that could arise due to beyond-Standard-Model physics. Over 300 million proton-electron coincidence events were used in a blind analysis with the result D = [ − 0.94±1.89 (stat)±0.97(sys)]×10^− 4. Assuming only vector and axial vector interactions in beta decay, our result can be interpreted as a measure of the phase of the axial-vector coupling relative to the vector coupling, φ_AV = 180.012 ° ± 0.028 °. This result also improves constrains on certain non-VA interactions.

[en] The rate of nuclear muon capture by the proton has been measured using a new technique based on a time projection chamber operating in ultraclean, deuterium-depleted hydrogen gas, which is key to avoiding uncertainties from muonic molecule formation. The capture rate from the hyperfine singlet ground state of the μp atom was obtained from the difference between the μ^- disappearance rate in hydrogen and the world average for the μ⁺ decay rate, yielding Λ_S=725.0±17.4 s^-1, from which the induced pseudoscalar coupling of the nucleon, g_P(q²=-0.88m_μ²)=7.3±1.1, is extracted

[en] Pair correlations in the ground state of ¹³⁰Te have been investigated using pair-transfer experiments to explore the validity of approximations in calculating the matrix element for neutrinoless double-β decay. This nucleus is a candidate for the observation of such decay, and a good understanding of its structure is crucial for eventual calculations of the neutrino mass, should such a decay indeed be observed. For proton-pair adding, strong transitions to excited 0⁺ states had been observed in the Te isotopes by Alford et al. [Nucl. Phys. A 323, 339 (1979)], indicating a breaking of the BCS approximation for protons in the ground state. We measured the neutron-pair removing (p,t) reaction on ¹³⁰Te and found no indication of a corresponding splitting of the BCS nature of the ground state for neutrons.

[en] Time reversal invariance violation is tightly constrained in the Standard Model, and the existence of a T-violating effect above the predicted level would be an indication of new physics. A sensitive probe of this symmetry in the weak interaction is the measurement of the D-coefficient in neutron decay. This parameter characterizes the triple-correlation of neutron spin, electron momentum, and neutrino (or proton) momentum, which changes sign under time reversal. The emiT experiment, now on line, attempts to improve the measurement of D, whose current average is 0.3±1.5x10^-3