Storage of ultracold neutrons in the UCN$\tau$ magneto-gravitational trap

Abstract

The UCN$\tau$ experiment is designed to measure the lifetime ${\tau }_n$ of the free neutron by trapping ultracold neutrons (UCN) in a magneto-gravitational trap. An asymmetric bowl-shaped NdFeB magnet Halbach array confines low-field-seeking UCN within the apparatus, and a set of electromagnetic coils in a toroidal geometry provide a background "holding" field to eliminate depolarization-induced UCN loss caused by magnetic field nodes. We present a measurement of the storage time ${\tau }_{store}$ of the trap by storing UCN for various times, and counting the survivors. The data are consistent with a single exponential decay, and we find ${\tau }_{store}=860\pm 19$ s: within $1\sigma$ of current global averages for ${\tau }_n$. The storage time with the holding field deactiveated is found to be ${\tau }_{store}=470\pm 160$ s; this decreased storage time is due to the loss of UCN which undergo Majorana spin-flips while being stored. We discuss plans to increase the statistical sensitivity of the measurement and investigate potential systematic effects.

6 pages, 5 figures

References in corpus (4)

• Improved Determination of the Neutron Lifetime
• Framework for maximum likelihood analysis of neutron beta decay observables to resolve the limits of the V-A law
• Limits on Tensor Coupling from Neutron $\beta$-Decay
• Ultracold neutron depolarization in magnetic bottles

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