Improved Neutron Lifetime Measurement with UCNτ.

We report an improved measurement of the free neutron lifetime τ_{n} using the UCNτ apparatus at the Los Alamos Neutron Science Center. We count a total of approximately 38×10^{6} surviving ultracold neutrons (UCNs) after storing in UCNτ's magnetogravitational trap over two data acquisition campaigns in 2017 and 2018. We extract τ_{n} from three blinded, independent analyses by both pairing long and short storage time runs to find a set of replicate τ_{n} measurements and by performing a global likelihood fit to all data while self-consistently incorporating the ß-decay lifetime. Both techniques achieve consistent results and find a value τ_{n}=877.75±0.28_{stat}+0.22/-0.16_{syst} s. With this sensitivity, neutron lifetime experiments now directly address the impact of recent refinements in our understanding of the standard model for neutron decay.

Search for the Neutron Decay n→X+γ, Where X is a Dark Matter Particle.

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 Monte Carlo 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% confidence.

Measurement of the neutron lifetime using a magneto-gravitational trap and in situ detection.

The precise value of the mean neutron lifetime, τn, plays an important role in nuclear and particle physics and cosmology. It is used to predict the ratio of protons to helium atoms in the primordial universe and to search for physics beyond the Standard Model of particle physics. We eliminated loss mechanisms present in previous trap experiments by levitating polarized ultracold neutrons above the surface of an asymmetric storage trap using a repulsive magnetic field gradient so that the stored neutrons do not interact with material trap walls. As a result of this approach and the use of an in situ neutron detector, the lifetime reported here [877.7 ± 0.7 (stat) +0.4/-0.2 (sys) seconds] does not require corrections larger than the quoted uncertainties.

A new method for measuring the neutron lifetime using an in situ neutron detector.

In this paper, we describe a new method for measuring surviving neutrons in neutron lifetime measurements using bottled ultracold neutrons (UCN), which provides better characterization of systematic uncertainties and enables higher precision than previous measurement techniques. An active detector that can be lowered into the trap has been used to measure the neutron distribution as a function of height and measure the influence of marginally trapped UCN on the neutron lifetime measurement. In addition, measurements have demonstrated phase-space evolution and its effect on the lifetime measurement.

Liquid chromatography solvent optimization: potential pitfalls when using a black box for developing a quality separation.

ICOS and DIAMOND are two commercially available, semi-automated HPLC solvent optimization software packages. The resultant optimized chromatographic separation is dependent on a combination of the operator's objective, the capability of the software system and the appropriateness of the data input. The latter contains components that represent the match between the requirements of the algorithms used and the information content of the data on which those algorithms operated. Knowledge about the sample content, stability and potential sample-solvent interactions can have a significant effect on the quality of the optimal solvent composition that is calculated. The results generated during the optimization of the separation of a mixture of U-83,757 and a variety of related compounds illustrate the need to consider the significance of the contribution to the calculated optimal separation of each of these potential pitfalls, both individually and in combination with the mode of operation of the relevant algorithms. Our results indicate that the quality of the final result is highly dependent on the intelligence content of the data used.

Automated HPLC optimization--not all systems are the same.

ICOS and DIAMOND are two LC solvent optimization software packages commercially available from Hewlett-Packard and Unicam, respectively. U-83,757 and various related compounds were chosen as the test mixture for the comparison of these systems. Chromatographic data were collected on both systems using the same 10 mobile phase compositions, equally spaced across an iso-eluotropic plane. The comparison focused on determining the performance of both packages with respect to the prediction of the mobile phase composition required to achieve an optimal separation. Both software systems are semi-automatic, with differing amounts of operator involvement required and employing slightly different approaches to interpolating peak movements between the 10 sets of data. The predicted optimal solvent compositions are evaluated in terms of the extent the information collected across the iso-eluotropic plane was used by the various algorithms in the two systems. Our results demonstrate the importance of comprehending the component operations involved in and the limitations of any software package that is used in analytical development. The operator should always remember that both systems are simply tools and design experiments appropriately, since the quality of the final result is highly dependent on a combination of the operator's objective, the capability of the system and the appropriateness of the data input.