The proton radius puzzle
Abstract
The proton size, specifically its charge radius, was thought known to about 1% accuracy. Now a new method probing the proton with muons instead of electrons finds a radius about 4% smaller, and to boot gives an uncertainty limit of about 0.1%. We review the different measurements, some of the calculations that underlie them, some of the suggestions that have been made to resolve the conflict, and give a brief overview new related experimental initiatives. At present, however, the resolution to the problem remains unknown.
- Publication:
-
Progress in Particle and Nuclear Physics
- Pub Date:
- May 2015
- DOI:
- 10.1016/j.ppnp.2015.01.002
- arXiv:
- arXiv:1502.05314
- Bibcode:
- 2015PrPNP..82...59C
- Keywords:
-
- Proton radius;
- Form factors;
- Muonic atoms;
- High Energy Physics - Phenomenology;
- Physics - Atomic Physics
- E-Print:
- Accepted invited review for Progress in Particle and Nuclear Physics. 28 pages, 15 figures