We have measured the \beta-\gamma directional correlation in the hindered decay ^22 \rmNa (3^+) \rightarrow ^22\rmNe (2^+) using the Gammasphere array at LBNL. Our measurement contributes to determining a complete set of weak form factors for the ^22Na \beta decay, testing corrections to allowed \beta decay to second recoil order. The aim is to resolve a long-standing discrepancy between experiment and allowed-order theory in the electron capture to positron emission ratios. We used a 6 \muCi source of ^22Na in the center of Gammasphere, a spherical array of 110 Ge detectors. The \beta^+ is detected with a 3 mm thick plastic scintillator with 8% solid angle. The \beta^+ decay is followed by a 1.275 MeV \gamma from the ^22Ne 2^+ state. We search for a directional dependence of the emitted \gamma's detected in coincidence with a \beta of form 1 + A\cos^2 \theta, with \theta the angle between the \beta and the individual Ge detectors, and A of order 10^-3. Variable Ge detector efficiency is normalized by dividing coincident \gamma counts by single 1.275 MeV \gamma's. Fitting the results versus \beta - \gamma angle using gates on the \beta^+ energy yields the energy-dependent A, which is sensitive to a linear combination of second-order form factors. Current data and analysis, and implications for ^22Na form factors will be presented.
[AD.02] Time Reversal in Polarized Neutron Decay---A Progress Report on the emiT Experiment
T.D. Steiger, M.C. Browne, S.R. Elliott, R.G.H. Robertson, J.F. Wilkerson (University of Washington), J. Anaya, T.J. Bowles, G.L. Greene, W.A. Teasdale (Los Alamos National Laboratory), J. Adams, M.S. Dewey, D. Gilliam, G.L. Jones, J.S. Nico, A.K. Thompson, F.E. Wietfeldt (National Institute of Standards and Technology), S.J. Freedman, B.K. Fujikawa, L.J. Lising, E.G. Wasserman (University of California at Berkeley / Lawrence Berkeley National Laboratory), K.P. Coulter, T.E. Chupp, S.-R. Hwang (University of Michigan), A. Garcia (University of Notre Dame)
The theory of neutron beta decay provides for the possibility of a violation of time-reversal (T) invariance due to the presence of a manifestly T-odd term. This term is a triple correlation involving the neutron spin and the momenta of the electron and neutrino decay products. The degree of correlation (usually denoted by the coefficient D) is determined by studying the decays of free, polarized neutrons in which the beta-decay electrons are detected in coincidence with recoil protons. The first run of the emiT experiment occurred from Dec. 1996 through most of 1997 at the Cold Neutron Research Facility, NIST. The target sensitivity to D is <10^-3, which may begin to restrict several extensions to the Standard Model that allow values of D in that range. Data from the first run will be discussed.
[AD.03] Time Reversal in Polarized Neutron Decay---Theory and Analysis for the emiT Experiment
L. J. Lising, S. J. Freedman, B. K. Fujikawa, E. G. Wasserman (Lawrence Berkeley National Laboratory), M.C. Browne, S. R. Elliott, R. G. H. Robertson, T. D. Steiger, J. F. Wilkerson (University of Washington), J.M. Adams, G. L. Jones, M. S. Dewey, J. S. Nico, A. K. Thompson, F. E. Wietfeldt (National Institute of Standards and Technology), T E. Chupp, K. P. Coulter, S.-R. Hwang (University of Michigan), A. Garcia (Notre Dame University), J.M. Anaya, T. J. Bowles, G. L. Greene, W. A. Teasdale (Los Alamos National Laboratory)
In the search for physics beyond the Standard Model, time reversal violation measurements provide strong insights, since the Standard Model predictions for most processes are so small as to be experimentally inaccessible. Hence, the emiT Experiment (see previous abstract) is measuring the D coefficient in free neutron decay. The Standard Model prediction for D (10^-12) is much smaller than the current experimental limit (0.3\pm1.5\times10^-3). However, extensions to the Standard Model including left-right symmetry, leptoquarks, and exotic fermions all allow values of D in the range 10^-5--10^-3. These predictions will be discussed with an eye toward underscoring the theoretical motivation of emiT. Also, the techniques employed to analyze the data will be outlined.
[AD.04] A New Measurement of the Partial \rm0^+\rightarrow0^+ Half Life of \rm^10C with GAMMASPHERE.
B.K. Fujikawa, S.J. Asztalos, C.J. Bowers, Y.-D. Chan, R.M. Clark, M.-A. Deleplanque-Stephens, P. Fallon, S.J. Freedman, K.T. Lesko, I.-Y. Lee, L.J. Lising, A.O. Macchiavelli, R.W. MacLeod, J.L. Mortara, C.L. Norris, C.E. Okada, M.C. Perillo-Isaac, J.C. Reich, D.W. Ross, M.A. Rowe, A. Schuelke, S.-Q. Shang, J. Stalnaker, F.S. Stephens, R.G. Stokstad, P.A. Vetter, E.G. Wasserman (University of California and the Lawrence Berkeley National Laboratory), J.P. Greene (Argonne National Laboratory)
We report on a new measurement of the branching ratio of the Superallowed Fermi transition in the beta decay of \rm^10C: \rm^10C(0^+,g.s.)\rightarrow ^10B(0^+,1.74MeV)+e^++\nu. This measurement was performed at the LBNL 88-inch cyclotron using 100 germanium detectors of the GAMMASPHERE facility. Precise knowledge of this branching ratio is necessary to compute the partial Fermi ft-value which in turn gives the weak vector coupling constant and the u-d element of the Cabibbo Kobayashi-Maskawa quark mixing matrix.
[AD.05] Precision test of the conserved vector current hypothesis with mass-14
Justin Mortara, Stuart Freedman, Brian Fujikawa (Lawrence Berkeley National Laboratory), Irshad Ahmad, John Greene, John Schiffer, Anthony Zeuli (Argonne National Laboratory)
We will report the result of a precision measurement of the shape factor
for the decay of ^14C performed with a superconducting solenoid at
Argonne National Laboratory. The electrons from the decay are transported
by the solenoidal field in small helical trajectories to a Si(Li)
detector. This configuration yields a large solid angle and eliminates
problems associated with scattering of electrons off of material
collimators which can lead to serious spectral distortions. The
implications of this measurement for a precision test of the conserved
vector current hypothesis in mass-14 will be discussed. An experiment
under development to measure the decay of ^14O will also be outlined.
[AD.06] Recent Work with Laser Trapped Radioactive ^21Na Atoms
Mary Rowe, Stuart Freedman, Brian Fujikawa, Gerald Gwinner, Song-Quan Shang, Paul Vetter (Lawrence Berkeley National Laboratory)
^21Na(t_1/2=22 seconds) is produced on-line at the 88" Cyclotron at LBNL
and is transferred to a magneto-optical trap where it is stored. Recent
improvements to our apparatus, mainly in our oven and target, have resulted
in 40,000 trapped ^21Na atoms. This number of atoms provides enough
activity for \beta-decay studies, our goal being precision measurements
of fundamental weak interaction parameters (for example from the
electron-neutrino correlations and the parity violating \beta-asymmetry
of spin-polarized nuclei). We have detected \beta's from our trapped
sample and are currently investigating transferring our atoms to a second
laser trap to provide a cleaner environment for \beta-decay studies. We
have also made a precise measurement of the atomic ground state hyperfine
splitting of ^21Na using our trapped atoms. We induce transitions between
the 3S_1/2(F=1) and the 3S_1/2(F=2) states with microwaves and probe
the atoms with a laser pulse. The atomic fluorescence measures how many
atoms make the transition as a function of microwave frequency. Our
resolution improves the precision on the ground state hyperfine splitting
by a factor of 100. This work is supported by DOE contract
DE-AC03-76SF00098.
[AD.07] Preliminary Results of the Mass-8 Beta-Decay Experiment
Marcus Beck, J.F. Amsbaugh, D.W. Storm, E. Swanson, J.P.S. van Schagen, D.C. Wright (University of Washington), L. De Braeckeleer (Duke University), K.B. Swartz (Yale University), Z. Zhao (McKinsey Co.)
The Mass-8 experiment tests the validity of the conservation of the vector current hypothesis and the existence of second class currents by comparing the weak magnetism and second class induced tensor form factors in the beta-delayed alpha-decays of ^8Li and ^8B with the magnetic form factor of the gamma-decay of the isobaric analogue state of ^8Be. The weak magnetism and second class tensor form factors can be extracted from the beta-alpha angular correlation of the beta decays while the magnetic form factor can be obtained from the M1 decay width of the gamma decay. Preliminary results on the beta-alpha angular correlation measurements of ^8Li and ^8B are presented. The main systematic uncertainty, the response function of the beta-counters, will be discussed.
[AD.08] Precision measurement of the ^4He(\alpha,\gamma)^8Be reaction
J.P.S. van Schagen, J.H. Gundlach, M.P. Kelly, K.A. Snover, D.W. Storm, D.C. Wright (University of Washington)
We are testing the Conservation of Vector Current hypothesis (CVC) and the possible existence of Second Class Currents (SCC) by comparing analog \beta and \gamma decays in the Mass-8 system(L. de Braeckeleer et al., Phys. Rev. C51, 2778 (1995)). An improved setup has been developed to measure the isovector M1 transition strength and the isovector E2/M1 mixing ratio from the 2^+ isobaric analog doublet at 17 MeV to the broad 2^+ final state at 3 MeV in ^8Be. This state is populated through the ^4He(\alpha,\gamma)^8Be radiative capture reaction at E_\alpha = 34 MeV. The \gamma-rays are detected with 3 large volume NaI-spectrometers with improved stabilization and QDC digitization. The experimental setup will be described and preliminary results will be presented.
[AD.09] Measurement of the Atomic Exchange Effect in the Beta Decay of ^63Ni.
N.E. Booth, L.C. Angrave, R.J. Gaitskell, A.D. Hahn, G.L. Salmon, A.M. Swift (Department of Physics, University of Oxford, Oxford OX1 3RH, UK.)
Precision measurements of the beta-decay spectrum of ^63Ni with a hermetic, calorimetric low-temperature detector have yielded evidence for the first time for the atomic exchange effect in beta decay. The exchange effect is due to the probability that the beta-decay electron is created into a bound state orbital of the daughter atom. Theoretical calculations by Harston and Pyper predict a small relative enhancement in the spectrum at low energies. In our experiment the energy release (apart from the neutrino energy) in each of 6 x 10^7 beta-decay events was measured by detecting the non-equilibrium phonons produced using series arrays of superconducting tunnel junctions fabricated on two InSb crystals which enclose the ^63Ni source. A relative enhancement at low energies is present in the data. The best-fit value of the exchange correction is 1.03 +/- 0.09(statistical) times the theoretical value, with a systematic error of +/- 0.15.
[AD.10] Magnetic Trapping of Ultra-cold Neutrons
J. Butterworth, C. Brome, P. Huffman, C. Mattoni, D. McKinsey, J. M. Doyle (Harvard University), K. Coakley, M. Dewey, D. Gilliam, F. Wietfeldt (NIST), G. Greene, S. Lamoreaux (LANL), K. Habicht, R. Golub (Hahn-Meitner Institut)
We describe progress towards magnetic trapping of ultra-cold neutrons and an improved measurement of the lifetime of the free neutron (\tau _ \beta). Ultra-cold neutrons will be confined in superfluid helium using a three-dimensional magnetic trap. Neutrons will undergo beta decay, with the recoiling electron producing XUV scintillations within the helium. Experimental cells have been developed that frequency down-convert the XUV to the visible. Fiber optics are used to transport the visible light out of the trapping region and into a photon detector. Tests of various cell designs and initial experimental results will be discussed.
[AD.11] Simulations of \beta ^+ - \nu Correlation Experiments in ^38mK and ^37K
O. Häusser (Simon Fraser University and TRIUMF), A. Gorelov (Simon Fraser University)
Positron-recoil coincidences in the presence of an electric field provide a promising way to investigate symmetry tests in nuclear \beta-decay from a neutral atom trap. In early 1997 the E715 collaboration at TRIUMF observed for the first time time-of-flight (TOF) spectra for trapped ^37,38mK and determined charge state fractions of Ar daughter recoil atoms. Detailed simulations have been carried out to study the effects of finite detector sizes on the TOF distributions for neutral and charged recoils. Two methods to extract a(^38mK) are described and achievable accuracies are discussed including possible systematic effects. It is also shown how the four non-zero correlation parameters a, A, B and c in ^37K can in principle be obtained from a series of measurements with polarized ^37K.
[AD.12] SPRT Analysis of Anomalies in Tritium Beta Decay Spectrum
T. Goldman (Los Alamos National Lab.), G.J. Stephenson Jr. (UNM)
The experimentally observed deviations from the Kurie plot near the endpoint of Tritium beta decay are opposite to those expected for the case of massive neutrinos. We reexamine(O. Kofoed-Hansen, Phil. Mag. 42), 1448 (1951). the possibility that these deviations are due to new hypoweak interactions. We find that enhancement above the massless neutrino beta spectrum does occur for all cases (scalar, pseudoscalar, tensor or right-handed currents), although it apparently cannot be large enough to explain the data and be consistent with other experimental constraints. Bounds on the strength of these non-standard model interactions are derived.
[AD.13] Nuclear Orientation of Tritium and Beryllium
Ludo Vanneste, Piet De Moor, Anja Van Geert, Natal Severijns (Leuven University)
Beta-decay of oriented tritium is reported for the first time, as well as first attempts at orienting and observing internal bremsstrahlung from oriented beryllium. Comparison is made to theoretical description of few nucleon systems.