A novel technique of extracting UCN lifetimes from storage bottle measurements dominated by scattering losses
arxiv(2023)
摘要
Neutron lifetime is a critical parameter in the Standard Model. Its
measurements using, particularly, the beamline and ultracold neutron storage
techniques reveals serious tension. The status of the tension between various
measurements have been presented, in light of the insights provided by the
β-decay correlation measurements. When ultracold neutrons are stored in
material bottles, they can be lost to various processes, such as β-decay
and up-scattering on material walls. Here, we revisit the lifetime measurement
in a material storage bottle, dominated by losses from scattering off the walls
of the storage chamber. The neutron energy spectra and its associated
uncertainties were, for the first time, well characterized. Such models have
been used in the extraction of mean time between wall bounces, which is a key
parameter for neutron storage disappearance experiments in search of neutron
oscillation. A comparison between the loss model and the number of neutrons
stored in a single chamber, used for the neutron electric dipole moment search,
allowed us to extract a neutron lifetime of
τ^*_n=879 (+158/-78)_stat. (+230/-114)_sys. s (68.3%
C.I.). Though the uncertainty on this lifetime is not competent with
currently available measurements, the highlight of this work is that, we
precisely identify the systematic sources of uncertainty that contribute to the
neutron lifetime measurements in material storage bottles, namely from the
uncertainty in the energy spectra, as well as the storage chamber parameters of
Fermi potential and loss per bounce parameter. In doing so, we finally
highlight the underestimation of the uncertainties in the previous Monte Carlo
simulations of experiments using ultracold neutron storage in material bottles.
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