L. J. Broussard

Determination of the axial-vector weak coupling constant with ultracold neutrons.

A precise measurement of the neutron decay β asymmetry A₀ has been carried out using polarized ultracold neutrons from the pulsed spallation ultracold neutron source at the Los Alamos Neutron Science Center. Combining data obtained in 2008 and 2009, we report A₀ = -0.119u200966±0.000u200989{-0.001u200940}{+0.001u200923}, from which we determine the ratio of the axial-vector to vector weak coupling of the nucleon g{A}/g{V}=-1.275u200990{-0.004u200945}{+0.004u200909}.

Search for the Neutron Decay n

Fornal and Grinstein recently proposed that the discrepancy between two different methods of neutron lifetime measurements, the beam and bottle methods, can be explained by a previously unobserved dark matter decay mode, n→X+γ. We perform a search for this decay mode over the allowed range of energies of the monoenergetic γ ray for X to be dark matter. A Compton-suppressed high-purity germanium detector is used to identify γ rays from neutron decay in a nickel-phosphorous-coated stainless-steel bottle. A combination of Montexa0Carlo and radioactive source calibrations is used to determine the absolute efficiency for detecting γ rays arising from the dark matter decay mode. We exclude the possibility of a sufficiently strong branch to explain the lifetime discrepancy with 97%xa0confidence.

\rightarrow

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).

X+

The 1+/2 -> 1+/2 superallowed mixed mirror decay of Ne-19 to F-19 is excellently suited for high precision studies of the weak interaction. However, there is some disagreement on the value of the half-life. In a new measurement we have determined this quantity to be T-1/2 = 17.2832 +/- 0.0051((stat)) +/- 0.0066((syst)) s, which differs from the previous world average by 3 standard deviations. The impact of this measurement on limits for physics beyond the standard model such as the presence of tensor currents is discussed.

\gamma

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.

where X is a dark matter particle.

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).

Precision Measurement of the Neutron Beta-Decay Asymmetry

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.