β Decay using Atom and Ion Traps

Recent advances in the techniques of atom and ion trapping have opened up a new vista in precision β decay studies due to the near-textbook source they provide: very cold (. 1 mK) and localized (. 1 cm), with an open geometry where the daughter particles escape with negligible distortions to their momenta. Atom traps: Magneto-optical traps (MOTs) have demonstrated the ability to measure the angular distribution of short-lived radioactive neutral atoms. Experiments using MOTs have placed stringent direct limits on a possible fundamental scalar current in the charged weak interaction via a precise measurement of the β − ν correlation parameter, aβν [1, 2]. These experiments continue to improve, along with others being developed to extend to other cases (for example, see A. Garćıa et al.’s contribution to this workshop on searching for tensor interactions using trapped He). Techniques are also being developed by the Trinat collaboration at Triumf to highly polarize lasercooled atoms via optical pumping. A proof-of-principle experiment measured the neutrino asymmetry parameter in K [3], with an improved version planned to take beam at Triumf in the summer of 2012. The contributions by J.A. Behr, R.J. Holt and L.A. Orozco to this workshop also describe other physics opportunities available using MOTs. Ion traps: Penning traps of ions are best known for the incredible precision with which they can measure masses: relative uncertainties of ∆M/M ≃ 10 have been reported on stable species [4], and ≃ 10 for very short-lived (& 10 ms) exotic ions [5]. These mass measurements have impacts in many fields of science, including fundamental physics research (CKM unitarity, testing nuclear models, correlation studies, etc.). Penning traps are also used in other applications, including laser spectroscopy, QED effects, electron-capture studies and the astrophysical r-process, to name a few. Opportunities at TREX: Our group at Texas A&M University are in the process of constructing a new doublePenning trap facility, Tamutrap, which will take advantage of the radioactive ion beam capabilities of the upgraded Cyclotron Institute facility, TREX [6]. The layout of the Institute’s cyclotrons and experimental equipment is shown in Fig. 1(a), where the components that are currently being built as part of the TREX upgrade are: re-commisioning the K150 cyclotron to deliver high intensity light particle and heavy ion beams; the light and heavy ion guide systems; the charge-breeding ECR ion source and coupling of it to the K500 cyclotron, to provide high quality re-accelerated rare beams of both neutron and proton rich isotopes in the 5 to 50 MeV/u range. Figure 1(b) shows the plans for the Penning trap facility in relation to the TREX upgrade. Radioactive beams for Tamutrap will be produced using the K150 cyclotron which will provide a high-intensity primary beam that will react with a target in front of “BigSol”, a large-acceptance 7-Tesla solenoid which will separate the desired products from deap inelastic reactions. An Argonne National Laboratory type gas-catcher [7] will collect these products and