Session D04: New Physics Searches at the Precision Frontier

Live

A nonzero permanent electric dipole moment (EDM) of a non-degenerate particle with spin implies the violation of time-reversal symmetry. Invoking the CPT theorem this also indicates the violation of the combined symmetry of charge conjugation and parity (CP). We present the result of an experiment to measure the EDM of the neutron at the Paul Scherrer Institute using Ramsey’s method of separated oscillating magnetic fields with ultracold neutrons. Our measurement stands in the long history of EDM experiments probing physics violating time reversal invariance. The salient features of this experiment were the use of a $^{199}$Hg co-magnetometer and an array of optically pumped cesium vapor magnetometers to cancel and correct for magnetic field changes. The statistical analysis was performed on blinded data sets by two separate groups while the estimation of systematic effects profited from an unprecedented knowledge of the magnetic field.   

Live

The difference between experiment and Standard-Model theory for the anomalous magnetic moment of the muon is, at over $3\sigma$, an important hint for new physics. The muon $g-2$ is sensitive to virtual effects of possible new particles and interactions, because it arises from quantum-mechanical loop effects in the Standard Model and therefore places important constraints on Standard-Model extensions. The Fermilab E989 experiment, which recently started running, and the planned J-PARC E34 experiment aim to reduce the experimental uncertainties by a factor of four. To leverage this anticipated improvement in experimental precision, and determine unambiguously whether or not new-physics effects contribute to this quantity, the theoretical errors must be made more reliable and reduced to a commensurate level. The Muon g-2 Theory Initiative was formed in 2017 to provide platforms that facilitate interactions between the different groups to consolidate the Standard-Model prediction and map out strategies for reducing the theory errors to keep pace with experiment. I will review the current status of Standard Model theory for this quantity and map out the future prospects.   

Live

We shall discuss the newest results on the proton charge radius, plus some history of the proton radius puzzle, giving an overall perspective and looking the whole suite of experimental results, with their interpretations and implications. We will also talk about controversies involving data reanalysis, whether the corresponding deuteron measurements indicate a lingering problem, and ask whether two photon exchange corrections are a barrier to the future improvements in accuracy of proton or light nucleus radius measurements.