A small proton charge radius from an electron-proton scattering experiment.

Journal Article (Journal Article)

Elastic electron-proton scattering (e-p) and the spectroscopy of hydrogen atoms are the two methods traditionally used to determine the proton charge radius, rp . In 2010, a new method using muonic hydrogen atoms1 found a substantial discrepancy compared with previous results2 , which became known as the 'proton radius puzzle'. Despite experimental and theoretical efforts, the puzzle remains unresolved. In fact, there is a discrepancy between the two most recent spectroscopic measurements conducted on ordinary hydrogen3,4 . Here we report on the proton charge radius experiment at Jefferson Laboratory (PRad), a high-precision e-p experiment that was established after the discrepancy was identified. We used a magnetic-spectrometer-free method along with a windowless hydrogen gas target, which overcame several limitations of previous e-p experiments and enabled measurements at very small forward-scattering angles. Our result, rp  = 0.831 ± 0.007stat  ± 0.012syst  femtometres, is smaller than the most recent high-precision e-p measurement5 and 2.7 standard deviations smaller than the average of all e-p experimental results6 . The smaller rp we have now measured supports the value found by two previous muonic hydrogen experiments1,7 . In addition, our finding agrees with the revised value (announced in 2019) for the Rydberg constant8 -one of the most accurately evaluated fundamental constants in physics.

Full Text

Duke Authors

Cited Authors

  • Xiong, W; Gasparian, A; Gao, H; Dutta, D; Khandaker, M; Liyanage, N; Pasyuk, E; Peng, C; Bai, X; Ye, L; Gnanvo, K; Gu, C; Levillain, M; Yan, X; Higinbotham, DW; Meziane, M; Ye, Z; Adhikari, K; Aljawrneh, B; Bhatt, H; Bhetuwal, D; Brock, J; Burkert, V; Carlin, C; Deur, A; Di, D; Dunne, J; Ekanayaka, P; El-Fassi, L; Emmich, B; Gan, L; Glamazdin, O; Kabir, ML; Karki, A; Keith, C; Kowalski, S; Lagerquist, V; Larin, I; Liu, T; Liyanage, A; Maxwell, J; Meekins, D; Nazeer, SJ; Nelyubin, V; Nguyen, H; Pedroni, R; Perdrisat, C; Pierce, J; Punjabi, V; Shabestari, M; Shahinyan, A; Silwal, R; Stepanyan, S; Subedi, A; Tarasov, VV; Ton, N; Zhang, Y; Zhao, ZW

Published Date

  • November 6, 2019

Published In

Volume / Issue

  • 575 / 7781

Start / End Page

  • 147 - 150

PubMed ID

  • 31695211

Electronic International Standard Serial Number (EISSN)

  • 1476-4687

International Standard Serial Number (ISSN)

  • 0028-0836

Digital Object Identifier (DOI)

  • 10.1038/s41586-019-1721-2


  • eng