Prof. Haiyan Gao and collaborators from Norfolk State University, North Carolina A&T State University and Mississippi State University have been awarded recently by the National Science Foundation a Major Research Instrumentation (MRI) grant for the construction of a cryogenic, internal hydrogen gas target for a new experiment on a precise measurement of the proton charge radius, a fundamental quantity important for both atomic and nuclear physics.
The recent development of the “proton radius crisis’’ refers to the intriguing fact that the proton charge radius determined from muonic hydrogen Lamb shift with 0.1% precision is about 7 σ smaller than those from electron scattering experiments and from electronic hydrogen Lamb shift measurements. Before one can determine whether the difference is due to new physics or not, new experiments both in lepton (electron and muon) scattering and atomic Lamb shift are crucial. Prof. Gao and collaborators proposed a new experiment at Jefferson Lab on electron-proton scattering using the combined technique of a high-precision electromagnetic calorimeter, an internal hydrogen gas target, and the well-known quantum electrodynamics electron-electron scattering to achieve a sub percent precision in unprecedentedly low momentum transfer squared. The experiment was approved by the Jefferson Lab Program Advisory Committee in June 2012 with the highest scientific rating. The experiment is expected to take data in the fall of 2014. For more details about this experiment, please visit the Medium Energy Physics Group page and see item #5.