Ultracold neutrons (UCNs) are a powerful tool for probing the Standard Model at high precision. The TRIUMF Ultracold Advanced Neutron (TUCAN) collaboration is building a new UCN source to provide ...unprecedented densities of UCNs for experiments. This source will use a tantalum-clad tungsten spallation target, receiving up to 40 µA of 480-MeV protons from TRIUMF’s main cyclotron. The beamline and target were constructed from 2014 to 2016 and operated at beam currents up to 10 µA from 2017 to 2019 as part of a prototype UCN source. We describe the design choices for the target and target-handling system, as well as our benchmarking of the target performance using UCN production measurements.
The present knowledge of Lamb shift, fine- and hyperfine structure of the 2S and 2P states in muonic deuterium is reviewed in anticipation of the results of a first measurement of several 2S −2P ...transition frequencies in muonic deuterium (μd). A term-by-term comparison of all available sources reveals reliable values and uncertainties of the QED and nuclear structure-dependent contributions to the Lamb shift, which are essential for a determination of the deuteron rms charge radius from μd. Apparent discrepancies between different sources are resolved, in particular for the difficult two-photon exchange contributions. Problematic single-sourced terms are identified which require independent recalculation.
Theory of the n = 2 levels in muonic helium-3 ions Franke, Beatrice; Krauth, Julian J.; Antognini, Aldo ...
The European physical journal. D, Atomic, molecular, and optical physics,
12/2017, Letnik:
71, Številka:
12
Journal Article
Recenzirano
Odprti dostop
The present knowledge of Lamb shift, fine-, and hyperfine structure of the 2S and 2P states in muonic helium-3 ions is reviewed in anticipation of the results of a first measurement of several 2S → ...2P transition frequencies in the muonic helium-3 ion,
μ
3He+. This ion is the bound state of a single negative muon
μ
-
and a bare helium-3 nucleus (helion),
3
He
++
. A term-by-term comparison of all available sources, including new, updated, and so far unpublished calculations, reveals reliable values and uncertainties of the QED and nuclear structure-dependent contributions to the Lamb shift and the hyperfine splitting. These values are essential for the determination of the helion rms charge radius and the nuclear structure effects to the hyperfine splitting in
μ
3He+. With this review we continue our series of theory summaries in light muonic atoms see A. Antognini et al., Ann. Phys.
331
, 127 (2013); J.J. Krauth et al., Ann. Phys.
366
, 168 (2016); and M. Diepold et al.
arXiv:1606.05231
(2016).
Graphical abstract
The energy levels of hydrogen-like atomic systems can be calculated with great precision. Starting from their quantum mechanical solution, they have been refined over the years to include the ...electron spin, the relativistic and quantum field effects, and tiny energy shifts related to the complex structure of the nucleus. These energy shifts caused by the nuclear structure are vastly magnified in hydrogen-like systems formed by a negative muon and a nucleus, so spectroscopy of these muonic ions can be used to investigate the nuclear structure with high precision. Here we present the measurement of two 2S-2P transitions in the muonic helium-4 ion that yields a precise determination of the root-mean-square charge radius of the α particle of 1.67824(83) femtometres. This determination from atomic spectroscopy is in excellent agreement with the value from electron scattering
, but a factor of 4.8 more precise, providing a benchmark for few-nucleon theories, lattice quantum chromodynamics and electron scattering. This agreement also constrains several beyond-standard-model theories proposed to explain the proton-radius puzzle
, in line with recent determinations of the proton charge radius
, and establishes spectroscopy of light muonic atoms and ions as a precise tool for studies of nuclear properties.
We provide an up to date summary of the theory contributions to the 2S → 2P Lamb shift and the fine structure of the 2P state in the muonic helium ion (μ{sup 4}He){sup +}. This summary serves as the ...basis for the extraction of the alpha particle charge radius from the muonic helium Lamb shift measurements at the Paul Scherrer Institute, Switzerland. Individual theory contributions needed for a charge radius extraction are compared and compiled into a consistent summary. The influence of the alpha particle charge distribution on the elastic two-photon exchange is studied to take into account possible model-dependencies of the energy levels on the electric form factor of the nucleus. We also discuss the theory uncertainty which enters the extraction of the {sup 3}He–{sup 4}He isotope shift from the muonic measurements. The theory uncertainty of the extraction is much smaller than a present discrepancy between previous isotope shift measurements. This work completes our series of n=2 theory compilations in light muonic atoms which we have performed already for muonic hydrogen, deuterium, and helium-3 ions.
We provide an up to date summary of the theory contributions to the 2S → 2P Lamb shift and the fine structure of the 2P state in the muonic helium ion (μ4He)+. This summary serves as the basis for ...the extraction of the alpha particle charge radius from the muonic helium Lamb shift measurements at the Paul Scherrer Institute, Switzerland. Individual theory contributions needed for a charge radius extraction are compared and compiled into a consistent summary. The influence of the alpha particle charge distribution on the elastic two-photon exchange is studied to take into account possible model-dependencies of the energy levels on the electric form factor of the nucleus. We also discuss the theory uncertainty which enters the extraction of the 3He–4He isotope shift from the muonic measurements. The theory uncertainty of the extraction is much smaller than a present discrepancy between previous isotope shift measurements. This work completes our series of n=2 theory compilations in light muonic atoms which we have performed already for muonic hydrogen, deuterium, and helium-3 ions.
The present knowledge of Lamb shift, fine- and hyperfine structure of the 2S and 2P states in muonic deuterium is reviewed in anticipation of the results of a first measurement of several transition ...frequencies in muonic deuterium (d). A term-by-term comparison of all available sources reveals reliable values and uncertainties of the QED and nuclear structure-dependent contributions to the Lamb shift, which are essential for a determination of the deuteron rms charge radius from d. Apparent discrepancies between different sources are resolved, in particular for the difficult two-photon exchange contributions. Problematic single-sourced terms are identified which require independent recalculation.
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