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Register a new userMeasurement of the fine-structure constant as a test of the Standard Model
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Measurements of the fine-structure constant alpha require methods from across subfields and are thus powerful tests of the consistency of theory and experiment in physics. Using the recoil frequency of cesium-133 atoms in a matter-wave interferometer, we recorded the most accurate measurement of the fine-structure constant to date: alpha = 1/137.035999046(27) at 2.0 x 10^-10 accuracy. Using multiphoton interactions (Bragg diffraction and Bloch oscillations), we demonstrate the largest phase (12 million radians) of any Ramsey-Borde interferometer and control systematic effects at a level of 0.12 parts per billion. Comparison with Penning trap measurements of the electron gyromagnetic anomaly ge-2 via the Standard Model of particle physics is now limited by the uncertainty in ge-2; a 2.5 sigma tension rejects dark photons as the reason for the unexplained part of the muons magnetic moment at a 99 percent confidence level. Implications for dark-sector candidates and electron substructure may be a sign of physics beyond the Standard Model that warrants further investigation.
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Radio-frequency electric-dipole transitions between nearly degenerate, opposite parity levels of atomic dysprosium (Dy) were monitored over an eight-month period to search for a variation in the fine-structure constant, $alpha$. The data provide a rate of fractional temporal variation of $alpha$ of $(-2.4pm2.3)times10^{-15}$ yr$^{-1}$ or a value of $(-7.8 pm 5.9) times 10^{-6}$ for $k_alpha$, the variation coefficient for $alpha$ in a changing gravitational potential. All results indicate the absence of significant variation at the present level of sensitivity. We also present initial results on laser cooling of an atomic beam of dysprosium.
Radio-frequency E1 transitions between nearly degenerate, opposite parity levels of atomic dysprosium were monitored over an eight month period to search for a variation in the fine-structure constant. During this time period, data were taken at different points in the gravitational potential of the Sun. The data are fitted to the variation in the gravitational potential yielding a value of $(-8.7 pm 6.6) times 10^{-6}$ for the fit parameter $k_alpha$. This value gives the current best laboratory limit. In addition, our value of $k_{alpha}$ combined with other experimental constraints is used to extract the first limits on k_e and k_q. These coefficients characterize the variation of m_e/m_p and m_q/m_p in a changing gravitational potential, where m_e, m_p, and m_q are electron, proton, and quark masses. The results are $k_e = (4.9 pm 3.9) times 10^{-5}$ and $k_q = (6.6 pm 5.2) times 10^{-5}$.
A means to extract the fine-structure constant $alpha$ from precision spectroscopic data on one-electron ions is presented. We show that in an appropriately weighted difference of the bound-electron $g$ factor and the ground state energy, nuclear structural effects can be effectively suppressed. This method is anticipated to deliver an independent value of $alpha$ via existing or near-future combined Penning trap and x-ray spectroscopic technology, and enables decreasing the uncertainty of $alpha$ by orders of magnitude.
Quasar absorption spectral data indicate the presence of a spatial gradient in the electromagnetic fine-structure constant $alpha$ on cosmological length scales. We point out that experiments with accelerometers, including torsion pendula and atom interferometers, can be used as sensitive probes of cosmological spatial gradients in the fundamental constants of nature, which give rise to equivalence-principle-violating forces on test masses. Using laboratory data from the Eot-Wash experiment, we constrain spatial gradients in $alpha$ along any direction to be $| boldsymbol{ abla} alpha / alpha | < 6.6 times 10^{-4}~(textrm{Glyr})^{-1}$ at $95%$ confidence level. Our result represents an order of magnitude improvement over laboratory bounds from clock-based searches for a spatial gradient in $alpha$ directed along the observed cosmological $alpha$-dipole axis. Improvements to accelerometer experiments in the foreseeable future are expected to provide sufficient sensitivity to test the cosmological $alpha$-dipole seen in astrophysical data.
We study electronic transitions in highly-charged Cf ions that are within the frequency range of optical lasers and have very high sensitivity to potential variations in the fine-structure constant, alpha. The transitions are in the optical despite the large ionisation energies because they lie on the level-crossing of the 5f and 6p valence orbitals in the thallium isoelectronic sequence. Cf16+ is a particularly rich ion, having several narrow lines with properties that minimize certain systematic effects. Cf16+ has very large nuclear charge and large ionisation energy, resulting in the largest alpha-sensitivity seen in atomic systems. The lines include positive and negative shifters.
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