Electrophobic Scalar Boson and Muonic Puzzles

Testing Quantum Electrodynamics with Exotic Atoms

Precision study of few-electron, high-Z ions is a privileged field for probing high-field, bound-state quantum electrodynamics (BSQED). However, the accuracy of such tests is plagued by nuclear uncertainties, which are often larger than the BSQED effects under investigation. We propose an alternative method with exotic atoms and show that transitions may be found between circular Rydberg states where nuclear contributions are vanishing while BSQED effects remain large. When probed with newly available quantum sensing detectors, these systems offer gains in sensitivity of 1 to 2 orders of magnitude, while the mean electric field largely exceeds the Schwinger limit.

Search for a Dark Leptophilic Scalar in e^{+}e^{-} Collisions

Many scenarios of physics beyond the standard model predict the existence of new gauge singlets, which might be substantially lighter than the weak scale. The experimental constraints on additional scalars with masses in the MeV to GeV range could be significantly weakened if they interact predominantly with leptons rather than quarks. At an e^{+}e^{-} collider, such a leptophilic scalar (ϕ_{L}) would be produced predominantly through radiation from a τ lepton. We report herein a search for e^{+}e^{-}→τ^{+}τ^{-}ϕ_{L}, ϕ_{L}→ℓ^{+}ℓ^{-} (ℓ=e, μ) using data collected by the BABAR experiment at SLAC. No significant signal is observed, and we set limits on the ϕ_{L} coupling to leptons in the range 0.04<m_{ϕ_{L}}<7.0  GeV. These bounds significantly improve upon the current constraints, excluding almost entirely the parameter space favored by the observed discrepancy in the muon anomalous magnetic moment below 4 GeV at 90% confidence level.

Check of the structure in photon pairs spectra at the invariant mass of about 38 MeV/c2

Results of analysis of the effective mass spectra of photon pairs produced in dC, dCu and pC interactions at momenta of 2.75, 3.83 and 5.5 GeV/c per nucleon, respectively, are presented. A structure at effective mass of about 38 MeV/c2 is observed. The results of testing the observed signal are presented. The test results support the conclusion that the observed signal is the consequence of detection of a particle with a mass of about 38 MeV/c2 decaying into a pair of photons.