This paper is a review of the present status of neutrino mass physics, which grew out of an APS sponsored study of neutrinos in 2004. After a discussion of the present knowledge of neutrino masses and mixing and some popular ways to probe the new physics implied by recent data, it summarizes what can be learned about neutrino interactions as well as the nature of new physics beyond the Standard Model from the various proposed neutrino experiments. The intriguing possibility that neutrino mass physics may be at the heart of our understanding of a long standing puzzle of cosmology, i.e. the origin of matter?antimatter asymmetry is also discussed.

/pdf/theory-of-neutrinos-a-white-paper-4bwov15tmt.pdf

Theory of neutrinos: a white paper

A Faraday rotation experiment can set limits on the magnetic moment of a electrically-neutral, dark-matter particle, and the limits increase in stringency as the candidate-particle mass decreases. Consequently, if we assume the dark-matter particle to be a thermal relic, our most stringent constraints emerge at the keV mass scale. We discuss how such an experiment could be realized and determine the limits on the magnetic moment as a function of mass which follow given demonstrated experimental capacities.

Shedding Light on Dark Matter: A Faraday Rotation Experiment to Limit a Dark Magnetic Moment

http://absimage.aps.org/image/APR09/MWS_APR09-2009-000941.pdf

R- and N-correlation coe_cients in neutron decay: Search for scalar and tensor couplings in weak interactions

Preliminary results from a neutron lifetime measurement using magnetically trapped neutrons are reported. Ultracold neutrons are loaded into a 1.1 T deep Ioffe-type trap through inelastic scattering of 0.89 nm neutrons with superfluid He. Decays of trapped neutrons are detected using the scintillation light produced by the interaction of energetic decay electrons with superfluid helium. The neutron trap lifetime after the suppression of above threshold neutrons with field ramping is measured to be 831± 58 s, consistent with other lifetime measurements. Studies of two leading systematic uncertainties: neutron absorption on He and the presence of above threshold neutrons are discussed in detail. Successful development of a 3.1 T deep Ioffe trap for the next generation apparatus is also described.

Towards Precision Measurement of the Neutron Lifetime using Magnetically Trapped Neutrons

This article reviews the status of an experiment to study the neutron spin-electron angular correlation with the Los Alamos Ultra-Cold Neutron (UCN) source. The experiment will generate UCNs from a novel solid deuterium, spallation source, and polarize them in a solenoid magnetic field. The experiment spectrometer will consist of a neutron decay region in a solenoid magnetic field combined with several different detector possibilities. An electron beam and a magnetic spectrometer will provide a precise, absolute calibration for these detectors. An A-correlation measurement with a relative precision of 0.2% is expected by the end of 2002.

/pdf/a-proposed-measurement-of-the-s-asymmetry-in-neutron-decay-305guaad1r.pdf

M. Fowler

Papers

A proposed measurement of the ß asymmetry in neutron decay with the Los Alamos Ultra-Cold Neutron Source