Dan Melconian

Experimental validation of the largest calculated isospin-symmetry-breaking effect in a superallowed Fermi decay.

A precision measurement of the γ yields following the β decay of (32)Cl has determined its isobaric-analogue branch to be (22.47(-0.18)(+0.21))%. Since it is an almost pure-Fermi decay, we can also determine the amount of isospin-symmetry breaking in this superallowed transition. We find a very large value, δ(C) = 5.3(9)%, in agreement with a shell-model calculation. This result sets a benchmark for isospin-symmetry-breaking calculations and lends support for similarly calculated, yet smaller, corrections that are currently applied to 0+ → 0 + transitions for tests of the standard model.

Precision Measurement of the Neutron Beta-Decay Asymmetry

A new measurement of the neutron β-decay asymmetry A_0 has been carried out by the UCNA Collaboration using polarized ultracold neutrons (UCNs) from the solid deuterium UCN source at the Los Alamos Neutron Science Center. Improvements in the experiment have led to reductions in both statistical and systematic uncertainties leading to A_0=−0.11954(55)_(stat)(98)_(syst), corresponding to the ratio of axial-vector to vector coupling λ ≡ g_A/g_V = −1.2756(30).

The Francium facility at TRIUMF

We present the current status of the Francium Trapping Facility at ISAC at TRIUMF. The facility will enable future experiments on the weak interaction with measurements of atomic parity non-conservation laser-cooled samples of artificially produced francium. These experiments require a precisely controlled environment, which the facility is designed to provide. The facility has been constructed and is being prepared for a series of commissioning runs.

Measurement of the neutron

We present a detailed report of a measurement of the neutron β-asymmetry parameter A_0, the parity-violating angular correlation between the neutron spin and the decay electron momentum, performed with polarized ultracold neutrons (UCN). UCN were extracted from a pulsed spallation solid deuterium source and polarized via transport through a 7-T magnetic field. The polarized UCN were then transported through an adiabatic-fast-passage spin-flipper field region, prior to storage in a cylindrical decay volume situated within a 1-T 2×2π solenoidal spectrometer. The asymmetry was extracted from measurements of the decay electrons in multiwire proportional chamber and plastic scintillator detector packages located on both ends of the spectrometer. From an analysis of data acquired during runs in 2008 and 2009, we report A_0=−0.11966±0.00089_(−0.00140)^(+0.00123), from which we extract a value for the ratio of the weak axial-vector and vector coupling constants of the nucleon, λ=g_A/g_V=−1.27590±0.00239_(−0.00377)^(+0.00331). Complete details of the analysis are presented.

\beta

We report a measurement of the nuclear polarization of laser-cooled, optically pumped 37K atoms which will allow us to precisely measure angular correlation parameters in the -decay of the same atoms. These results will be used to test the V − A framework of the weak interaction at high precision. At the Triumf neutral atom trap (Trinat), a magneto-optical trap confines and cools neutral 37K atoms and optical pumping spin-polarizes them. We monitor the nuclear polarization of the same atoms that are decaying in situ by photoionizing a small fraction of the partially polarized atoms and then use the standard optical Bloch equations to model their population distribution. We obtain an average nuclear polarization of , which is significantly more precise than previous measurements with this technique. Since our current measurement of the β-asymmetry has statistical uncertainty, the polarization measurement reported here will not limit its overall uncertainty. This result also demonstrates the capability to measure the polarization to , allowing for a measurement of angular correlation parameters to this level of precision, which would be competitive in searches for new physics.

-asymmetry parameter

The FrPNC collaboration has begun the construction of an on-line laser cooling and trapping apparatus at TRIUMF to measure atomic parity non-conservation (PNC) and the nuclear anapole moment in a string of artificially produced francium isotopes. Atomic PNC experiments provide unique high precision tests of the electroweak sector of the Standard Model at very low energies. Furthermore, precision measurements of spin-dependent atomic PNC can determine nuclear anapole moments and probe the weak force within the nucleus. Francium is an excellent candidate for precision measurements of atomic PNC due to its simple electronic structure and enhanced parity violation: both the optical PNC and anapole moment signals are expected to be over an order of magnitude larger than in cesium.

A_0

A new measurement of the neutron β-decay asymmetry A_0 has been carried out by the UCNA Collaboration using polarized ultracold neutrons (UCNs) from the solid deuterium UCN source at the Los Alamos Neutron Science Center. Improvements in the experiment have led to reductions in both statistical and systematic uncertainties leading to A_0=−0.11954(55)_(stat)(98)_(syst), corresponding to the ratio of axial-vector to vector coupling λ ≡ g_A/g_V = −1.2756(30).

with ultracold neutrons

We present a detailed report of a measurement of the neutron β-asymmetry parameter A_0, the parity-violating angular correlation between the neutron spin and the decay electron momentum, performed with polarized ultracold neutrons (UCN). UCN were extracted from a pulsed spallation solid deuterium source and polarized via transport through a 7-T magnetic field. The polarized UCN were then transported through an adiabatic-fast-passage spin-flipper field region, prior to storage in a cylindrical decay volume situated within a 1-T 2×2π solenoidal spectrometer. The asymmetry was extracted from measurements of the decay electrons in multiwire proportional chamber and plastic scintillator detector packages located on both ends of the spectrometer. From an analysis of data acquired during runs in 2008 and 2009, we report A_0=−0.11966±0.00089_(−0.00140)^(+0.00123), from which we extract a value for the ratio of the weak axial-vector and vector coupling constants of the nucleon, λ=g_A/g_V=−1.27590±0.00239_(−0.00377)^(+0.00331). Complete details of the analysis are presented.

Precision measurement of the nuclear polarization in laser-cooled, optically pumped 37 K

Since the first cyclotron beam fifty years ago, the Texas A&M Cyclotron Institute has functioned as a university-based laboratory. Over the past two decades it has been funded by the U.S. Department of Energy, the State of Texas, the Welch Foundation, and commercial sale of beam-time. The first accelerator is a conventional isochronous cyclotron modeled after the 88″ cyclotron at the Lawrence Berkeley Laboratory. It arose from a proposal funded by the U.S. Atomic Energy Commission, the R. A. Welch Foundation (a private foundation headquartered in Houston), and the State of Texas and continued to operate from 1967 to 1987. After recommissioning in 2007 as a higher-field K150 machine, it is still in operation. The K500 cyclotron, funded in 1980 by the Welch Foundation and Texas A&M University and modeled after the Michigan State NSCL K500 cyclotron, is a superconducting isochronous cyclotron whose first beam was extracted in 1988.