Duke Physics graduate student Weizhi Xiong in Prof. Haiyan Gao’s group is the lead author of a paper on "A small proton charge radius from an electron–proton scattering experiment" which appeared in Nature (online) on November 6, 2019 at 18:00 (London time), November 6, 2019 at 13:00 (US Eastern Time). This is a major result in resolving the proton charge radius puzzle that started in 2010 and refers to the large discrepancy between the ultra-high precise results obtained from muonic hydrogen Lamb Shift measurements and those from electron-proton scattering and hydrogen spectroscopic measurements.
To resolve this, Gao and collaborators set out to do a completely new type of electron scattering experiment with a number of innovations. They opted out of traditional magnetic spectrometers, instead used an electromagnetic calorimeter and Electron Gas Multiplier (GEM) detectors in order to reach unprecedented forward electron scattering angles. They also used for the first time an open-ended, cryogenically cooled hydrogen gas flowing target on the beam line at the Department of Energy’s Thomas Jefferson National Accelerator Facility in Newport News, Virginia. They detected electrons scattered from both the proton and the electron inside the hydrogen atom at the same time with the latter serving as an excellent reference process. Their experiment found a small proton charge radius that is in agreement with the muonic hydrogen result.
Prof. Haiyan Gao and her group played an important role in this experiment. A number of Duke graduate students and postdocs including Chao Peng, Weizhi Xiong, Chao Gu, Xuefei Yan, Mehdi Meziane, and Zhihong Ye contributed enormously over the years in all aspects of this innovative and challenging experiment. Prof. Gao is one of the spokespersons of this experiment, and also a co-PI of a NSF’s Major Research Instrumentation grant for the construction of the windowless hydrogen gas flowing target.
Find the paper online at Nature's site here. The news was picked up by the Duke Research Blog. Read "How Small is a Proton? Smaller Than Anyone Thought" here. Jefferson Lab also posted a news release that can be seen here.
Photo: Duke Physics graduate student Weizhi Xiong and Prof. Haiyan Gao
