Atoms

19 pages, 1488 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Towards an Improved Test of the Standard Model’s Most Precise Prediction

by G. Gabrielse, S. E. Fayer, T. G. Myers and X. Fan

Atoms 2019, 7(2), 45; https://doi.org/10.3390/atoms7020045 - 25 Apr 2019

Cited by 29 | Viewed by 6778

The electron and positron magnetic moments are the most precise prediction of the standard model of particle physics. The most accurate measurement of a property of an elementary particle has been made to test this result. A new experimental method is now being [...] Read more.

The electron and positron magnetic moments are the most precise prediction of the standard model of particle physics. The most accurate measurement of a property of an elementary particle has been made to test this result. A new experimental method is now being employed in an attempt to improve the measurement accuracy by an order of magnitude. Positrons from a “student source” now suffice for the experiment. Progress toward a new measurement is summarized. Full article

(This article belongs to the Special Issue High Precision Measurements of Fundamental Constants)

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9 pages, 1034 KB

Open AccessEditor’s ChoiceArticle

Testing Quantum Coherence in Stochastic Electrodynamics with Squeezed Schrödinger Cat States

by Wayne Cheng-Wei Huang and Herman Batelaan

Atoms 2019, 7(2), 42; https://doi.org/10.3390/atoms7020042 - 5 Apr 2019

Cited by 12 | Viewed by 4612

Abstract

The interference pattern in electron double-slit diffraction is a hallmark of quantum mechanics. A long-standing question for stochastic electrodynamics (SED) is whether or not it is capable of reproducing such effects, as interference is a manifestation of quantum coherence. In this study, we [...] Read more.

The interference pattern in electron double-slit diffraction is a hallmark of quantum mechanics. A long-standing question for stochastic electrodynamics (SED) is whether or not it is capable of reproducing such effects, as interference is a manifestation of quantum coherence. In this study, we used excited harmonic oscillators to directly test this quantum feature in SED. We used two counter-propagating dichromatic laser pulses to promote a ground-state harmonic oscillator to a squeezed Schrödinger cat state. Upon recombination of the two well-separated wavepackets, an interference pattern emerges in the quantum probability distribution but is absent in the SED probability distribution. We thus give a counterexample that rejects SED as a valid alternative to quantum mechanics. Full article

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17 pages, 2099 KB

Open AccessEditor’s ChoiceArticle

Radiative Transition Parameters in Atomic Lanthanum from Pseudo-Relativistic Hartree–Fock and Fully Relativistic Dirac–Hartree–Fock Calculations

by Sébastien Gamrath, Patrick Palmeri and Pascal Quinet

Atoms 2019, 7(1), 38; https://doi.org/10.3390/atoms7010038 - 20 Mar 2019

Cited by 9 | Viewed by 3700

Abstract

Calculated radiative transition probabilities and oscillator strengths are reported for 392 lines of neutral lanthanum (La I) atom in the spectral range from the near ultraviolet to the mid infrared. They were obtained using two different theoretical methods based on the pseudo-relativistic Hartree–Fock [...] Read more.

Calculated radiative transition probabilities and oscillator strengths are reported for 392 lines of neutral lanthanum (La I) atom in the spectral range from the near ultraviolet to the mid infrared. They were obtained using two different theoretical methods based on the pseudo-relativistic Hartree–Fock (HFR) and the fully relativistic multiconfiguration Dirac–Hartree–Fock (MCDHF) approaches, both including the most important intravalence and core-valence electron correlations. The quality of these radiative parameters was assessed through detailed comparisons between the results obtained using different physical models and between our theoretical results and the experimental data, where available. Of the total number of La I lines listed in the present work, about 60% have gf- and gA-values determined for the first time. Full article

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23 pages, 327 KB

Open AccessEditor’s ChoiceReview

High-Precision Atomic Mass Measurements for Fundamental Constants

by Edmund G. Myers

Atoms 2019, 7(1), 37; https://doi.org/10.3390/atoms7010037 - 18 Mar 2019

Cited by 35 | Viewed by 7224

Abstract

Atomic mass measurements are essential for obtaining several of the fundamental constants. The most precise atomic mass measurements, at the 10⁻¹⁰ level of precision or better, employ measurements of cyclotron frequencies of single ions in Penning traps. We discuss the relation of [...] Read more.

Atomic mass measurements are essential for obtaining several of the fundamental constants. The most precise atomic mass measurements, at the 10⁻¹⁰ level of precision or better, employ measurements of cyclotron frequencies of single ions in Penning traps. We discuss the relation of atomic masses to fundamental constants in the context of the revised SI. We then review experimental methods, and the current status of measurements of the masses of the electron, proton, neutron, deuteron, tritium, helium-3, helium-4, oxygen-16, silicon-28, rubidium-87, and cesium-133. We conclude with directions for future work. Full article

(This article belongs to the Special Issue High Precision Measurements of Fundamental Constants)

27 pages, 564 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Theory of the Anomalous Magnetic Moment of the Electron

by Tatsumi Aoyama, Toichiro Kinoshita and Makiko Nio

Atoms 2019, 7(1), 28; https://doi.org/10.3390/atoms7010028 - 22 Feb 2019

Cited by 384 | Viewed by 18216

Abstract

The anomalous magnetic moment of the electron

a_{e}

measured in a Penning trap occupies a unique position among high precision measurements of physical constants in the sense that it can be compared directly with the theoretical calculation based on the renormalized quantum [...] Read more.

The anomalous magnetic moment of the electron

a_{e}

measured in a Penning trap occupies a unique position among high precision measurements of physical constants in the sense that it can be compared directly with the theoretical calculation based on the renormalized quantum electrodynamics (QED) to high orders of perturbation expansion in the fine structure constant

α

, with an effective parameter

α / π

. Both numerical and analytic evaluations of

a_{e}

up to

{(α / π)}^{4}

are firmly established. The coefficient of

{(α / π)}^{5}

has been obtained recently by an extensive numerical integration. The contributions of hadronic and weak interactions have also been estimated. The sum of all these terms leads to

a_{e} (theory)

=

1 159 652 181.606 (11) (12) (229) \times 10^{- 12}

, where the first two uncertainties are from the tenth-order QED term and the hadronic term, respectively. The third and largest uncertainty comes from the current best value of the fine-structure constant derived from the cesium recoil measurement:

α^{- 1} (Cs) = 137.035 999 046 (27)

. The discrepancy between

a_{e} (theory)

and

a_{e} ((experiment))

is 2.4

σ

. Assuming that the standard model is valid so that

a_{e}

(theory) =

a_{e}

(experiment) holds, we obtain

α^{- 1} (a_{e}) = 137.035 999 1496 (13) (14) (330)

, which is nearly as accurate as

α^{- 1} (Cs)

. The uncertainties are from the tenth-order QED term, hadronic term, and the best measurement of

a_{e}

, in this order. Full article

(This article belongs to the Special Issue High Precision Measurements of Fundamental Constants)

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12 pages, 409 KB

Open AccessEditor’s ChoiceArticle

Capture Cross Sections and Radiative Emission-Line Strengths for Slow Ne⁸⁺ Collisions with He and H₂

by Anthony C. K. Leung and Tom Kirchner

Atoms 2019, 7(1), 15; https://doi.org/10.3390/atoms7010015 - 23 Jan 2019

Cited by 3 | Viewed by 3687

Abstract

The Ne⁸⁺–He and –H₂ collision systems are examined at impact speeds ranging between 0.17 and 0.4 a.u. Transition probabilities for electron capture are obtained using the two-center basis generator method performed within the independent-electron model. The aim of calculating capture [...] Read more.

The Ne⁸⁺–He and –H₂ collision systems are examined at impact speeds ranging between 0.17 and 0.4 a.u. Transition probabilities for electron capture are obtained using the two-center basis generator method performed within the independent-electron model. The aim of calculating capture cross sections for these collision systems is to provide new theoretical verification of previously reported experimental data and to provide aid for astrophysical X-ray studies. This study also examines the applicability of the independent-electron model with effective potentials to describe two-electron capture for these two systems. Comparisons of capture cross sections and radiative-emission counts with the available experimental and theoretical data show an overall good agreement. Full article

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19 pages, 1063 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Two-Photon Vibrational Transitions in ¹⁶O₂⁺ as Probes of Variation of the Proton-to-Electron Mass Ratio

by Ryan Carollo, Alexander Frenett and David Hanneke

Atoms 2019, 7(1), 1; https://doi.org/10.3390/atoms7010001 - 20 Dec 2018

Cited by 15 | Viewed by 4783

Abstract

Vibrational overtones in deeply-bound molecules are sensitive probes for variation of the proton-to-electron mass ratio

μ

. In nonpolar molecules, these overtones may be driven as two-photon transitions. Here, we present procedures for experiments with

^{16} O_{2}^{+}

, including state-preparation through [...] Read more.

Vibrational overtones in deeply-bound molecules are sensitive probes for variation of the proton-to-electron mass ratio

μ

. In nonpolar molecules, these overtones may be driven as two-photon transitions. Here, we present procedures for experiments with

^{16} O_{2}^{+}

, including state-preparation through photoionization, a two-photon probe, and detection. We calculate transition dipole moments between all

X^{2} Π_{g}

vibrational levels and those of the

A^{2} Π_{u}

excited electronic state. Using these dipole moments, we calculate two-photon transition rates and AC-Stark-shift systematics for the overtones. We estimate other systematic effects and statistical precision. Two-photon vibrational transitions in

^{16} O_{2}^{+}

provide multiple routes to improved searches for

μ

variation. Full article

(This article belongs to the Special Issue High Precision Measurements of Fundamental Constants)

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19 pages, 5766 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Measurements of the Neutron Lifetime

by F. E. Wietfeldt

Atoms 2018, 6(4), 70; https://doi.org/10.3390/atoms6040070 - 10 Dec 2018

Cited by 24 | Viewed by 8898

Abstract

Free neutron decay is a fundamental process in particle and nuclear physics. It is the prototype for nuclear beta decay and other semileptonic weak particle decays. Neutron decay played a key role in the formation of light elements in the early universe. The [...] Read more.

Free neutron decay is a fundamental process in particle and nuclear physics. It is the prototype for nuclear beta decay and other semileptonic weak particle decays. Neutron decay played a key role in the formation of light elements in the early universe. The precise value of the neutron mean lifetime, about 15 min, has been the subject of many experiments over the past 70 years. The two main experimental methods, the beam method and the ultracold neutron storage method, give average values of the neutron lifetime that currently differ by 8.7 s (4 standard deviations), a serious discrepancy. The physics of neutron decay, implications of the neutron lifetime, previous and recent experimental measurements, and prospects for the future are reviewed. Full article

(This article belongs to the Special Issue High Precision Measurements of Fundamental Constants)

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