Related papers: The Mu-MASS (MuoniuM lAser SpectroScopy) experimen…
Measuring the muon anomalous magnetic moment g-2 and the rare decays of light pseudoscalar mesons into lepton pair P \to l+l- serve as important test of the standard model. To reduce the theoretical uncertainty in the standard model…
The status of the muon (g-2) experiment at the Brookhaven AGS is reviewed. An accuracy of 1.3 ppm on the mu^+ anomalous magnetic moment has been achieved and published. This result differs with the standard model prediction by about 2.5…
Searches for charged lepton flavor violation in the muon sector stand out among the most sensitive and clean probes for physics beyond the Standard Model. Currently, $\mu^+ \to \mathrm{e}^+ \gamma$ experiments provide the best constraints…
Positronium and Muonium are purely leptonic atoms and hence free of an internal sub-structure. This qualifies them as potentially well suited systems to probe the existence of physics beyond the Standard Model. We hence carry out a…
This White Paper briefly reviews the present status of the muon (g-2) experiment and the physics motivation for a new effort. The present comparison between experiment and theory indicates a tantalizing $3.4 \sigma$ deviation. An…
The MuCap experiment at the Paul Scherrer Institute has measured the rate L_S of muon capture from the singlet state of the muonic hydrogen atom to a precision of 1%. A muon beam was stopped in a time projection chamber filled with 10-bar,…
The "proton radius puzzle" is the 7-standard-deviations difference of the charge radius of the proton as determined from the Lamb shift in electronic hydrogen and elastic electron scattering off the proton on the one side and the high…
The anomalous magnetic moments of leptons represent excellent probes of the Standard Model and therefore also of possible new physics effects. In particular, the persisting hint of new physics in the muon $g$-2 motivates the investigation…
High precision spectroscopy can provide a sensitive tool to test Coulomb's law on atomic length scales. This can then be used to constrain particles such as extra "hidden" photons or minicharged particles that are predicted in many…
Our recent series of measurements at Brookhaven National Laboratory determined the muon anomalous magnetic moment \amu to a precision of 0.5 ppm. The final result--representing the average of five running periods using both positive and…
We present the status and the prospects of the ongoing efforts to improve the measurements of the 1S-2S transition in positronium and muonium. These purely leptonic systems represent ideal objects to test bound-state QED to high precision…
The situation of the experimental data used in the dispersive evaluation of the hadronic vacuum polarization contribution to the anomalous magnetic moment of the muon is assessed in view of two recent measurements: $e^+e^- \to \pi^+\pi^-$…
In light of the upcoming measurement of the muon anomalous magnetic moment (g-2), we revisit the corrections to g-2 in the context of the $SU(4)_L \times U(1)_X$ gauge symmetry. We investigate three models based on this gauge symmetry and…
The QED hadronic vacuum polarization function plays an important role in the determination of precision electroweak observables and of the anomalous magnetic moment of the muon. These contributions have been computed from data, by means of…
The next generation of "intensity frontier" facilities will bring a significant increase in the intensity of sub-relativistic beams of $\mu^-$. We show that the use of these beams in combination with thin targets of $Z\sim 30$ elements…
We examine the prospects for discovering new physics through muon dipole moments. The current deviation in $g_{\mu}-2$ may be due entirely to the muon's {\em electric} dipole moment. We note that the precession frequency in the proposed BNL…
Muonic atom spectroscopy -- the measurement of the x rays emitted during the formation process of a muonic atom -- has a long standing history in probing the shape and size of nuclei. In fact, almost all stable elements have been subject to…
The "proton size puzzle" and the "muon anomalous moment problem" are incomplete descriptions of significant discrepancies of Standard Model calculations with experiments. What is particularly new is that the experiments and theory confront…
The 4.2$\sigma$ discrepancy between the standard model prediction for the muon anomalous magnetic moment $a_\mu$ and the experimental result is accompanied by other anomalies. A crucial input for the prediction is the hadronic vacuum…
In view of the recently observed discrepancy of theory and experiment for muonic hydrogen [R. Pohl et al., Nature vol. 466, p. 213 (2010)], we reexamine the theory on which the quantum electrodynamic (QED) predictions are based. In…