The proton radius puzzle is an unanswered problem in physics relating to the size of the proton.[1] Historically the proton charge radius was measured by two independent methods, which converged to a value of about 0.877 femtometres (1 fm = 10−15 m). This value was challenged by a 2010 experiment using a third method, which produced a radius about 4% smaller than this, at 0.842 femtometres.[2] New experimental results reported in the autumn of 2019 agree with the smaller measurement, as does a re-analysis of older data published in 2022. While some believe that this difference has been resolved,[3][4] this opinion is not yet universally held.[5][6]
- ^ Krauth, J. J.; Schuhmann, K.; Abdou Ahmed, M.; Amaro, F. D.; Amaro, P.; et al. (2 June 2017). The proton radius puzzle. 52nd Rencontres de Moriond EW 2017. La Thuile, Aosta Valley. arXiv:1706.00696. Bibcode:2017arXiv170600696K. Presentation slides (19 March 2017).
- ^ Pohl R, Antognini A, Nez F, Amaro FD, Biraben F, et al. (July 2010). "The size of the proton" (PDF). Nature. 466 (7303): 213–216. Bibcode:2010Natur.466..213P. doi:10.1038/nature09250. PMID 20613837. S2CID 4424731.
- ^ Hammer, Hans-Werner; Meißner, Ulf-G. (2020). "The proton radius: From a puzzle to precision". Science Bulletin. 65 (4): 257–258. arXiv:1912.03881. Bibcode:2020SciBu..65..257H. doi:10.1016/j.scib.2019.12.012. PMID 36659086. S2CID 208909979.
- ^ R.L. Workman et al. (Particle Data Group), Prog.Theor.Exp.Phys. 2022, 083C01 (2022), The Review of Particle Physics (2022), Particle listing – Proton, page 7: "the puzzle appears to be resolved."
- ^ Karr, Jean-Philippe; Marchand, Dominique (2019). "Progress on the proton-radius puzzle". Nature. 575 (7781): 61–62. Bibcode:2019Natur.575...61K. doi:10.1038/d41586-019-03364-z. PMID 31695215.
- ^ Hill, Heather (6 November 2019). "Proton radius puzzle may be solved". Physics Today. doi:10.1063/PT.6.1.20191106a. ISSN 1945-0699. S2CID 241132004.