Grant: Subatomic Physics Envelope - Research Tools and Instruments

We use laser trapping and cooling techniques to capture radioactive atoms and precisely test the Standard Model of the weak interaction. Confined in a 1 mm-sized cloud, the nuclei undergo beta decay, producing three products: a positron, a neutrino, and a daughter nucleus. The daughter moves slowly and would stop in a nm of material, but it freely escapes the trap. By detecting it in coincidence with the positron, we can measure the momentum and hence the angular distribution of neutrinos more directly than in previous experiments.  The known electroweak interaction is mediated by spin-1 vector bosons, the W+, W-, and Z0. These only produce left-handed neutrinos: parity (mirror symmetry) is maximally violated. We test these model features.  We have published the best general limits on scalar interactions coupling to the 1st generation of particles by measuring the beta-neutrino correlation in the pure Fermi decay of a spin-0 nucleus. We propose to improve these measurements by a factor of 3, and to extend the experiment to lower beta energies to enhance sensitivity to certain types of the scalar interactions. The goal is to be sensitive to possible SUSY contributions.This equipment request is for instrumentation to allow the upgraded experiment to proceed. Most of this is improvements in the instrumentation to detect the daughter nuclei. The new micro-channel plate assembly would let all the recoils be detected, to eliminate acceptance systematic errors and enhance the statistics. The position-sensitive readout would be upgraded to a newer delay-line anode technology, producing fewer nonlinear distortions and counting at the high count rates needed.The equipment would also enhance the spin-polarized part of the program, searching for couplings to wrong-handed neutrinos and to additional types of interactions. In particular it would allow enhanced collection of recoils in coincidence with beta detectors parallel to the polarization axis, a new correlation which would be independent of systematic effects from isospin mixing. 2 Ph.D. students and 1 undergrad will begin experiments with this equipment, and a new expert low-energy ion postdoc will assist its implementation.