Speaker
Helene Fleurbaey
(NIST)
Description
The CODATA-recommended value of the proton rms charge radius $r_p$ is based on hydrogen/deuterium spectroscopy and electron–proton/deuteron scattering experiments. Since 2010, a discrepancy between the $r_p$ value determined from muonic hydrogen spectroscopy and the CODATA-recommended value has led to intense research activity both in theory and experiment. The situation has recently become even more puzzling as a contradiction appeared between two new hydrogen spectroscopy results: the 2S-4P transition frequency [Beyer $\textit{et al.}$, Science 358, 2017] agrees with the muonic $r_p$ value, while the 1S-3S transition frequency presented here supports the CODATA value.
In our experiment at Laboratoire Kastler Brossel (Paris, France), the two-photon 1S-3S hydrogen transition is excited in an atomic beam, with a continuous-wave 205-nm laser obtained by sum frequency generation in a non-linear crystal. The transition frequency is measured with respect to the LNE-SYRTE Cs clock by means of a frequency comb. The second-order Doppler shift and other systematic effects have been included in the analysis to determine the 1S-3S transition frequency with a relative uncertainty of $9\times10^{-13}$ [Fleurbaey $\textit{et al.}$, PRL accepted for publication, 2018]. The value of the proton radius which can be inferred is in very good agreement with the CODATA-recommended value.
In this talk, I will present the current situation of the proton radius puzzle and our latest results.
| [email protected] |
Primary author
Helene Fleurbaey
(NIST)
