# 56. International Winter Meeting on Nuclear Physics

22-26 January 2018
Bormio, Italy
Europe/Berlin timezone

## Status of the proton radius puzzle

25 Jan 2018, 12:00
30m
Bormio, Italy

#### Bormio, Italy

Overview Talk Fundamental Interactions

### Speaker

Prof. Randolf Pohl (Johannes Gutenberg University Mainz)

### Description

Laser spectroscopy of muonic hydrogen [1,2] yielded a proton rms charge radius which is 4% (or ~6 sigmas) smaller than the CODATA value [3]. Also the deuteron charge radius from muonic deuterium [4] is 6 sigmas smaller than the CODATA value, but consistent with the smaller proton inside the deuteron. These smaller charge radii, when combined with precision measurements of the 1S-2S transitions in regular (electronic) hydrogen [5] and deuterium [6], yield a 6 sigmas smaller value of the Rydberg constant [7], compared to the CODATA value. In this talk I will report about a new measurement of the Rydberg constant from the 2S-4P transition in regular hydrogen performed in Garching [8], which supports the smaller, "muonic" value. I will also discuss the measurements in muonic hydrogen, deuterium, and helium, and the consequences for the "proton radius puzzle". [1] Pohl et al. (CREMA Coll.), Nature 466, 213 (2010) [2] Antognini et al. (CREMA Coll.), Science 339, 417 (2013) [3] Mohr et al. (CODATA 2014), Rev. Mod. Phys. 88, 035009 (2016) [4] Pohl et al. (CREMA Coll.), Science 353, 669 (2016) [5] Parthey et al., PRL 107, 203001 (2011) [6] Parthey et al., PRL 104, 233001 (2010) [7] Pohl et al., Metrologia 54, L1 (2017) [8] Beyer et al., Science 358, 79 (2017)

### Summary

Laser spectroscopy of muonic hydrogen [1,2] yielded a proton rms charge radius
which is 4% (or ~6 sigmas) smaller than the CODATA value [3]. Also the deuteron
charge radius from muonic deuterium [4] is 6 sigmas smaller than the CODATA
value, but consistent with the smaller proton inside the deuteron.

These smaller charge radii, when combined with precision measurements of the
1S-2S transitions in regular (electronic) hydrogen [5] and deuterium [6], yield
a 6 sigmas smaller value of the Rydberg constant [7], compared to the CODATA value.

In this talk I will report about a new measurement of the Rydberg constant from
the 2S-4P transition in regular hydrogen performed in Garching [8], which
supports the smaller, "muonic" value. I will also discuss the measurements in
muonic hydrogen, deuterium, and helium, and the consequences for the "proton

[1] Pohl et al. (CREMA Coll.), Nature 466, 213 (2010)
[2] Antognini et al. (CREMA Coll.), Science 339, 417 (2013)
[3] Mohr et al. (CODATA 2014), Rev. Mod. Phys. 88, 035009 (2016)
[4] Pohl et al. (CREMA Coll.), Science 353, 669 (2016)
[5] Parthey et al., PRL 107, 203001 (2011)
[6] Parthey et al., PRL 104, 233001 (2010)
[7] Pohl et al., Metrologia 54, L1 (2017)
[8] Beyer et al., Science 358, 79 (2017)

### Primary author

Prof. Randolf Pohl (Johannes Gutenberg University Mainz)

 Slides