We have set limits on contributions of scalar interactions to nuclear beta decay. A magneto-optical trap provides a localized source of atoms suspended in space, so the low-energy recoiling nuclei can freely escape and be detected in coincidence with the beta. This allows reconstruction of the neutrino momentum, and the measurement of the beta-nu correlation, in a more direct fashion than previously possible. The beta-nu correlation parameter of the 0(+)-->0(+) pure Fermi decay of (38)K(m) is a =0.9981+/-0.0030+0.0032 / -0.0037, consistent with the standard model prediction a =1.

We review the use of laser cooling and trapping for Standard Model tests, focusing on trapping of radioactive isotopes. Experiments with neutral atoms trapped using modern laser cooling techniques are testing several basic predictions of electroweak unification. For nuclear β decay, demonstrated trap techniques include neutrino momentum measurements from beta-recoil coincidences, along with methods to produce highly polarized samples. These techniques have set the best general constraints on non-Standard Model scalar interactions in the first generation of particles. They also have the promise to test whether parity symmetry is maximally violated, to search for tensor interactions, and to search for new sources of time reversal violation. There are also possibilites for exotic particle searches. Measurements of the strength of the weak neutral current can be assisted by precision atomic experiments using traps loaded with small numbers of radioactive atoms, and sensitivity to possible time-reversal violating electric dipole moments can be improved.

We have measured the hyperfine splitting of the 7P 1/2 state at the 100 ppm level in Fr isotopes ( 206g,206m,207,209,213,221 Fr) near the closed neutron shell (N = 126 in 213 Fr). The measurements in five isotopes and a nuclear isomeric state of francium, combined with previous determinations of the 7S 1/2 splittings, reveal the spatial distribution of the nuclear magnetization, i.e. the Bohr-Weisskopf effect. We compare our results with a simple shell model consisting of unpaired single valence nucleons orbiting a spherical nucleus, and find good agreement over a range of neutron-deficient isotopes ( 207−213 Fr). Also, we find near-constant proton anomalies for several even-N isotopes. This identifies a set of Fr isotopes whose nuclear structure can be understood well enough for the extraction of weak interaction parameters from parity non-conservation studies.PACS numbers: 21.10. Gv,27.80.+w,32.10.Fn Weak interaction studies in heavy atoms require for their interpretation precise knowledge of the atomic and nuclear wavefunctions. To extract nucleon-nucleon weak interaction couplings from the weak interaction induced parityviolating anapole moment [1], nuclei with simple and regular magnetic properties are desirable [2-4]. The nuclear magnetic moment is used to benchmark nuclear structure theories for calculating the anapole moment [3], which is a contact field effect produced inside the finite extent of the nucleus. Here we explore the regularity of the magnetic properties of a chain of Fr isotopes and find that 207−213 Fr in the vicinity of the neutron shell closure mark a range where the nuclear structure is sufficiently tractable for standard model tests and constraints on new physics [5].To lowest order, the atomic hyperfine interaction can be described using a point-like nucleus characterized by the magnetic dipole moment. Deviations from the pointlike approximation of the nucleus, referred to as hyperfine anomalies, come from considering how finite magnetic and charge distributions affect the interaction between the magnetization of the nucleus and the magnetic field created by the electrons. The magnetic contribution is known as the Bohr-Weisskopf (BW) effect [6,7]. The difference in the nuclear charge distribution (Breit-Rosenthal (BR) effect [23][24][25]) produces very small variations between isotopes, leaving the BW effect dominant [26,27]. As a new generation of proposed parity violation experiments in atoms (including Fr) and molecules starts [8][9][10][11][12][13][14], it is important to understand the limiting factors due to the nuclear structure, e.g. the nuclear magnetization, for the interpretation Fr with up to 6 neutron holes, we find near-constant magnetic hyperfine anomalies for the odd-Z, even-N isotopes [15]. The neutron rich odd-even isotope 221 Fr shows a different behavior due to the deformation of the nucleus. The odd-Z, odd-N isotopes have anomaly contributions from both the proton and the valence neutron.BW effect measurements usually require precise knowledge of both, hyper...

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A new technique, full neutrino momentum reconstruction, is used to set limits on the admixture of heavy neutrinos into the electron neutrino. We measure coincidences between nuclear recoils and positrons from the beta decay of trapped radioactive atoms and deduce the neutrino momentum. A search for peaks in the reconstructed recoil time-of-flight spectrum as a function of positron energy is performed. The admixture upper limits range from 4 x 10(-3) to 2 x 10(-2) and are the best direct limits for neutrinos (as opposed to antineutrinos) for the mass region of 0.7 to 3.5 MeV.