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19 pages, 1488 KiB

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 27 | Viewed by 6120

Abstract

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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27 pages, 564 KiB

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 331 | Viewed by 14323

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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19 pages, 1063 KiB

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 13 | Viewed by 4085

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 KiB

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 22 | Viewed by 7323

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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15 pages, 739 KiB

Open AccessArticle

Optical Pumping of TeH⁺: Implications for the Search for Varying m_p/m_e

by Patrick R. Stollenwerk, Mark G. Kokish, Antonio G. S. De Oliveira-Filho, Fernando R. Ornellas and Brian C. Odom

Atoms 2018, 6(3), 53; https://doi.org/10.3390/atoms6030053 - 17 Sep 2018

Cited by 14 | Viewed by 4048

Abstract

Molecular overtone transitions provide optical frequency transitions sensitive to variation in the proton-to-electron mass ratio (

μ \equiv m_{p} / m_{e}

). However, robust molecular state preparation presents a challenge critical for achieving high precision. Here, we characterize infrared and optical-frequency [...] Read more.

Molecular overtone transitions provide optical frequency transitions sensitive to variation in the proton-to-electron mass ratio (

μ \equiv m_{p} / m_{e}

). However, robust molecular state preparation presents a challenge critical for achieving high precision. Here, we characterize infrared and optical-frequency broadband laser cooling schemes for TeH

^{+}

, a species with multiple electronic transitions amenable to sustained laser control. Using rate equations to simulate laser cooling population dynamics, we estimate the fractional sensitivity to

μ

attainable using TeH

^{+}

. We find that laser cooling of TeH

^{+}

can lead to significant improvements on current

μ

variation limits. Full article

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

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10 pages, 351 KiB

Open AccessFeature PaperArticle

Oriented Polar Molecules in a Solid Inert-Gas Matrix: A Proposed Method for Measuring the Electric Dipole Moment of the Electron

by A. C. Vutha, M. Horbatsch and E. A. Hessels

Atoms 2018, 6(1), 3; https://doi.org/10.3390/atoms6010003 - 5 Jan 2018

Cited by 45 | Viewed by 7045

Abstract

We propose a very sensitive method for measuring the electric dipole moment of the electron using polar molecules embedded in a cryogenic solid matrix of inert-gas atoms. The polar molecules can be oriented in the

\hat{z}

-direction by an applied electric field, [...] Read more.

We propose a very sensitive method for measuring the electric dipole moment of the electron using polar molecules embedded in a cryogenic solid matrix of inert-gas atoms. The polar molecules can be oriented in the

\hat{z}

-direction by an applied electric field, as has recently been demonstrated by Park et al. The trapped molecules are prepared into a state that has its electron spin perpendicular to

\hat{z}

, and a magnetic field along

\hat{z}

causes precession of this spin. An electron electric dipole moment

d_{e}

would affect this precession due to the up to 100 GV/cm effective electric field produced by the polar molecule. The large number of polar molecules that can be embedded in a matrix, along with the expected long coherence times for the precession, allows for the possibility of measuring

d_{e}

to an accuracy that surpasses current measurements by many orders of magnitude. Because the matrix can inhibit molecular rotations and lock the orientation of the polar molecules, it may not be necessary to have an electric field present during the precession. The proposed technique can be applied using a variety of polar molecules and inert gases, which, along with other experimental variables, should allow for careful study of systematic uncertainties in the measurement. Full article

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

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4691 KiB

Open AccessFeature PaperArticle

Proton Charge Radius from Electron Scattering

by Ingo Sick

Atoms 2018, 6(1), 2; https://doi.org/10.3390/atoms6010002 - 30 Dec 2017

Cited by 24 | Viewed by 5562

Abstract

The rms-radius R of the proton charge distribution is a fundamental quantity needed for precision physics. This radius, traditionally determined from elastic electron-proton scattering via the slope of the Sachs form factor

G_{e} (q^{2})

extrapolated to momentum transfer [...] Read more.

The rms-radius R of the proton charge distribution is a fundamental quantity needed for precision physics. This radius, traditionally determined from elastic electron-proton scattering via the slope of the Sachs form factor

G_{e} (q^{2})

extrapolated to momentum transfer

q^{2} = 0

, shows a large scatter. We discuss the approaches used to analyze the e-p data, partly redo these analyses in order to identify the sources of the discrepancies and explore alternative parameterizations. The problem lies in the model dependence of the parameterized

G (q)

needed for the extrapolation. This shape of

G (q

<

q_{m i n})

is closely related to the shape of the charge density

ρ (r)

at large radii r, a quantity that is ignored in most analyses. When using our physics knowledge about this large-r density together with the information contained in the high-q data, the model dependence of the extrapolation is reduced, and different parameterizations of the pre-2010 data yield a consistent value for

R = 0.887 \pm 0.012

fm. This value disagrees with the more precise value

0.8409 \pm 0.0004

fm determined from the Lamb shift in muonic hydrogen. Full article

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

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801 KiB

Open AccessFeature PaperArticle

Long-Range Interactions for Hydrogen: 6P–1S and 6P–2S Systems

by Ulrich D. Jentschura and Chandra M. Adhikari

Atoms 2017, 5(4), 48; https://doi.org/10.3390/atoms5040048 - 23 Nov 2017

Cited by 7 | Viewed by 4005

Abstract

The collisional shift of a transition constitutes an important systematic effect in high-precision spectroscopy. Accurate values for van der Waals interaction coefficients are required in order to evaluate the distance-dependent frequency shift. We here consider the interaction of excited hydrogen

6 P

atoms [...] Read more.

The collisional shift of a transition constitutes an important systematic effect in high-precision spectroscopy. Accurate values for van der Waals interaction coefficients are required in order to evaluate the distance-dependent frequency shift. We here consider the interaction of excited hydrogen

6 P

atoms with metastable atoms (in the

2 S

state), in order to explore the influence of quasi-degenerate

2 P

and

6 S

states on the dipole-dipole interaction. The motivation for the calculation is given by planned high-precision measurements of the transition. Due to the presence of quasi-degenerate levels, one can use the non-retarded approximation for the interaction terms over wide distance ranges. Full article

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

3729 KiB

Open AccessArticle

THz/Infrared Double Resonance Two-Photon Spectroscopy of HD⁺ for Determination of Fundamental Constants

by Florin Lucian Constantin

Atoms 2017, 5(4), 38; https://doi.org/10.3390/atoms5040038 - 12 Oct 2017

Cited by 9 | Viewed by 3940

Abstract

A double resonance two-photon spectroscopy scheme is discussed to probe jointly rotational and rovibrational transitions of ensembles of trapped HD⁺ ions. The two-photon transition rates and lightshifts are calculated with the two-photon tensor operator formalism. The rotational lines may be observed with [...] Read more.

A double resonance two-photon spectroscopy scheme is discussed to probe jointly rotational and rovibrational transitions of ensembles of trapped HD⁺ ions. The two-photon transition rates and lightshifts are calculated with the two-photon tensor operator formalism. The rotational lines may be observed with sub-Doppler linewidth at the hertz level and good signal-to-noise ratio, improving the resolution in HD⁺ spectroscopy beyond the 10⁻¹² level. The experimental accuracy, estimated at the 10⁻¹² level, is comparable with the accuracy of theoretical calculations of HD⁺ energy levels. An adjustment of selected rotational and rovibrational HD⁺ lines may add clues to the proton radius puzzle, may provide an independent determination of the Rydberg constant, and may improve the values of proton-to-electron and deuteron-to-proton mass ratios beyond the 10⁻¹¹ level. Full article

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

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Review

Jump to: Research

23 pages, 327 KiB

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 31 | Viewed by 5806

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)

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