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At least 1,333 records · Page 74
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DOE OSTI2019

Ground-state electromagnetic moments of Ca 37

The hyperfine coupling constants of neutron deficient 37 Ca were deduced from the atomic hyperfine spectrum of the 4 s 2 S 1/2 ↔ 4 p 2 P 3/2 transition in Ca II , measured using the collinear laser spectroscopy technique. The ground-state magnetic-dipole and spectroscopic electric-quadrupole moments were observed for the first time as μ=+0.7453(72)μ N and Q = -15(11) e 2 fm 2 , respectively. The experimental values agree well with nuclear shell-model calculations using the universal sd model-space Hamiltonians versions A and B (USDA/B) in the sd -model space with a 95% probability of the canonical nucleon configuration. It is demonstrated that the magnetic moment of 39 Ca requires a larger non- sd -shell component than that of 37 Ca for good agreement with the shell-model calculation, suggests a more robust closed subshell structure of 36 Ca at the neutron number N =16 than 40 Ca. The results are also compared to valence-space in-medium similarity renormalization group calculations based on chiral two- and three-nucleon interactions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2019

Model-independent form-factor constraints for electromagnetic spin-1 currents

Using local gauge invariance in the form of the Ward-Takahashi identity and the fact that properly constructed current operators must be free of kinematic singularities, it is shown that the magnetic moment μ and the quadrupole moment Q of an elementary spin-1 particle with mass m and charge e are related by 2mμ + m 2 Q = e, thus constraining the normalizations of the Sachs form factors. This relation holds true as a matter of course at the tree level in the standard model, but we prove that it remains true in general for dressed spin-1 states derived from elementary fields. Furthermore, general expressions for spin-1 propagators and currents with arbitrary hadronic dressing are given, which show that the result is independent of any dressing effect or model approach.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2019

Electromagnetic backgrounds and potassium-42 activity in the DEAP-3600 dark matter detector

The DEAP-3600 experiment is searching for weakly interacting massive particles dark matter with a 3.3 × 10 3 kg single phase liquid argon (LAr) target, located 2.1 km underground at SNOLAB. The experimental signature of dark matter interactions is kilo electron volt–scale 40 Ar nuclear recoils producing 128 nm LAr scintillation photons observed by photomultiplier tubes. The largest backgrounds in DEAP-3600 are electronic recoils (ERs) induced by β and γ rays originating from internal and external radioactivity in the detector material. A background model of the ER interactions in DEAP-3600 was developed and is described in this work. The model is based on several components which are expected from radioisotopes in the LAr, from ex situ material assay measurements, and from dedicated independent in situ analyses. This prior information is used in a Bayesian fit of the ER components to a 247.2 d dataset to model the radioactivity in the surrounding detector materials. Pulse-shape discrimination separates ER and NR events. However, detailed knowledge of the ER background and activity of detector components sets valuable constraints on NR backgrounds including neutrons and alphas. In addition, the activity of 42 Ar in LAr in DEAP-3600 is determined by measuring the daughter decay of 42 K. Finally, this cosmogenically activated trace isotope is a relevant background at higher energies for other rare event searches using atmospheric argon, e.g., DarkSide-20k, GERDA, or LEGEND. The specific activity of 42 Ar in the atmosphere is found to be 40.4 ± 5.9 μ Bq/kg of argon.

79 ASTRONOMY AND ASTROPHYSICS↗