Lamb shift in muonic hydrogen and the proton charge radius puzzle
Prof. Krzysztof Pachucki (University of Warsaw)

Measurements of the proton charge radius from the muon-proton and the electron-proton interactions lead to different values.
The resulting 4% discrepancy can not be explained neither within the Standard Model (SM), nor by its known extensions. It is because any new interaction would violate the SM precision tests, such as the muon magnetic anomaly. The only reasonable solution within SM is the striking hypothesis, that precise measurements of both the hydrogen specrum and the low-energy electron-proton scattering are somehow incorrect. I will present in my lecture the current status of our knowledge on the proton charge radius and describe planned measurements to resolve the puzzle.