A measurement of the atomic hydrogen Lamb shift and the proton charge radius

Science ◽  
2019 ◽  
Vol 365 (6457) ◽  
pp. 1007-1012 ◽  
Author(s):  
N. Bezginov ◽  
T. Valdez ◽  
M. Horbatsch ◽  
A. Marsman ◽  
A. C. Vutha ◽  
...  
Keyword(s):  
Direct Measurement ◽  
Charge Radius ◽  
Atomic Hydrogen ◽  
Lamb Shift ◽  
Shift Measurement ◽  
Proton Radius ◽  
Proton Charge ◽  
Proton Charge Radius ◽  
Proton Radius Puzzle

The surprising discrepancy between results from different methods for measuring the proton charge radius is referred to as the proton radius puzzle. In particular, measurements using electrons seem to lead to a different radius compared with those using muons. Here, a direct measurement of the n = 2 Lamb shift of atomic hydrogen is presented. Our measurement determines the proton radius to be rp = 0.833 femtometers, with an uncertainty of ±0.010 femtometers. This electron-based measurement of rp agrees with that obtained from the analogous muon-based Lamb shift measurement but is not consistent with the larger radius that was obtained from the averaging of previous electron-based measurements.

scholarly journals Two-photon frequency comb spectroscopy of atomic hydrogen

Science ◽  
2020 ◽  
Vol 370 (6520) ◽  
pp. 1061-1066 ◽  
Author(s):  
Alexey Grinin ◽  
Arthur Matveev ◽  
Dylan C. Yost ◽  
Lothar Maisenbacher ◽  
Vitaly Wirthl ◽  
...  
Keyword(s):  
Quantum Electrodynamics ◽  
Atomic Hydrogen ◽  
Frequency Comb ◽  
Muonic Hydrogen ◽  
Significant Discrepancy ◽  
Two Photon ◽  
Proton Radius ◽  
Proton Charge ◽  
Proton Charge Radius ◽  
Proton Radius Puzzle

We have performed two-photon ultraviolet direct frequency comb spectroscopy on the 1S-3S transition in atomic hydrogen to illuminate the so-called proton radius puzzle and to demonstrate the potential of this method. The proton radius puzzle is a significant discrepancy between data obtained with muonic hydrogen and regular atomic hydrogen that could not be explained within the framework of quantum electrodynamics. By combining our result [f1S-3S = 2,922,743,278,665.79(72) kilohertz] with a previous measurement of the 1S-2S transition frequency, we obtained new values for the Rydberg constant [R∞ = 10,973,731.568226(38) per meter] and the proton charge radius [rp = 0.8482(38) femtometers]. This result favors the muonic value over the world-average data as presented by the most recent published CODATA 2014 adjustment.

What do we actually know about the proton radius?

1999 ◽  
Vol 77 (4) ◽  
pp. 241-266 ◽  
Author(s):  
S G Karshenboim
Keyword(s):  
Charge Radius ◽  
Lamb Shift ◽  
Elastic Electron ◽  
Proton Scattering ◽  
Proton Radius ◽  
Proton Charge ◽  
Proton Charge Radius

This paper considers the different determinations of the proton charge radius. It demonstrates that the results from the elastic electron-proton scattering have to be assigned a higher uncertainty. A review of the hydrogen Lamb-shift measurements and the radius determination from them is also presented.PACS No.: 27.10 and 35.10B

Solution to the proton radius puzzle

2014 ◽  
Vol 23 (12) ◽  
pp. 1450090 ◽  
Author(s):  
D. Robson
Keyword(s):  
Form Factor ◽  
Electron Scattering ◽  
Charge Radius ◽  
Rest Frame ◽  
Muonic Hydrogen ◽  
Electric Form Factor ◽  
Scattering Data ◽  
Proton Radius ◽  
Proton Charge Radius ◽  
Proton Radius Puzzle

The relationship between the static electric form factor for the proton in the rest frame and the Sachs electric form factor in the Breit momentum frame is used to provide a value for the difference in the mean squared charge radius of the proton evaluated in the two frames. Associating the muonic–hydrogen data analysis for the proton charge radius of 0.84087 fm with the rest frame and associating the electron scattering data with the Breit frame yields a prediction of 0.87944 fm for the proton radius in the relativistic frame. The most recent value deduced via electron scattering from the proton is 0.877(6) fm so that the frame dependence used here yields a plausible solution to the proton radius puzzle.

The muonic hydrogen Lamb-shift experiment

2005 ◽  
Vol 83 (4) ◽  
pp. 339-349 ◽  
Author(s):  
R Pohl ◽  
A Antognini ◽  
F D Amaro ◽  
F Biraben ◽  
J MR Cardoso ◽  
...  
Keyword(s):  
Charge Radius ◽  
Quantum Electrodynamics ◽  
Lamb Shift ◽  
Laser System ◽  
Bound State ◽  
Muonic Hydrogen ◽  
X Rays ◽  
Large Area ◽  
Proton Charge ◽  
Proton Charge Radius

The charge radius of the proton, the simplest nucleus, is known from electron-scattering experiments only with a surprisingly low precision of about 2%. The poor knowledge of the proton charge radius restricts tests of bound-state quantum electrodynamics (QED) to the precision level of about 6 × 10–6, although the experimental data themselves (1S Lamb shift in hydrogen) have reached a precision of 2 × 10–6. The determination of the proton charge radius with an accuracy of 10–3 is the main goal of our experiment, opening a way to check bound-state QED predictions to a level of 10–7. The principle is to measure the 2S–2P energy difference in muonic hydrogen (µ–p) by infrared laser spectroscopy. The first data were taken in the second half of 2003. Muons from our unique very-low-energy muon beam are stopped at a rate of ~100 s–1 in 0.6 mbar H2 gas where the lifetime of the formed µp(2S) atoms is about 1.3 µs. An incoming muon triggers a pulsed multistage laser system that delivers ~0.2 mJ at λ ≈ 6 µm. Following the laser excitation µp(2S) → µp(2P) we observe the 1.9 keV X-rays from 2P–1S transitions using large area avalanche photodiodes. The resonance frequency, and, hence, the Lamb shift and the proton radius, is determined by measuring the intensity of these X-rays as a function of the laser wavelength. A broad range of laser frequencies was scanned in 2003 and the analysis is currently under way. PACS Nos.: 36.10.Dr, 14.20.Dh, 42.62.Fi

scholarly journals Status of the muonic hydrogen Lamb-shift experiment

2007 ◽  
Vol 85 (5) ◽  
pp. 469-478 ◽  
Author(s):  
T Nebel ◽  
F D Amaro ◽  
A Antognini ◽  
F Biraben ◽  
J MR Cardoso ◽  
...  
Keyword(s):  
Charge Radius ◽  
Lamb Shift ◽  
Bound State ◽  
Muonic Hydrogen ◽  
X Ray ◽  
Proton Charge ◽  
Proton Charge Radius ◽  
Experimental Apparatus ◽  
Shift Experiment ◽  
Bound State Qed

The Lamb-shift experiment in muonic hydrogen (μ– p) aims to measure the energy difference between the [Formula: see text] atomic levels to a precision of 30 ppm. This would allow the r.m.s. proton charge radius rp to be deduced to a precision of 10–3 and open a way to check bound-state quantum electrodynamics (QED) to a level of 10–7. The poor knowledge of the proton charge radius restricts tests of bound-state QED to the precision level of about 6 × 10–6, although the experimental data themselves (Lamb-shift in hydrogen) have reached a precision of  × 10–6. Values for rp not depending on bound-state QED results from electron scattering experiments have a surprisingly large uncertainty of 2%. In our Lamb-shift experiment, low-energy negative muons are stopped in low-density hydrogen gas, where, following the μ– atomic capture and cascade, 1% of the muonic hydrogen atoms form the metastable 2S state with a lifetime of about 1 μs. A laser pulse at λ ≈ 6 μm is used to drive the 2S → 2P transition. Following the laser excitation, we observe the 1.9 keV X-ray being emitted during the subsequent de-excitation to the 1S state using large-area avalanche photodiodes. The resonance frequency and, hence, the Lamb shift and the proton charge radius are determined by measuring the intensity of the X-ray fluorescence as a function of the laser wavelength. The results of the run in December 2003 were negative but, nevertheless, promising. One by-product of the 2003 run was the first observation of the short-lived 2S component in muonic hydrogen. Currently, improvements in the laser-system, the experimental apparatus, and the data acquisition are being implemented. PACS Nos.: 36.10.Dr, 14.20.Dh, 42.62.Fi

The Lamb shift in muonic hydrogenThis paper was presented at the International Conference on Precision Physics of Simple Atomic Systems, held at École de Physique, les Houches, France, 30 May – 4 June, 2010.

2011 ◽  
Vol 89 (1) ◽  
pp. 37-45 ◽  
Author(s):  
Randolf Pohl ◽  
Aldo Antognini ◽  
François Nez ◽  
Fernando D. Amaro ◽  
François Biraben ◽  
...  
Keyword(s):  
Charge Radius ◽  
Lamb Shift ◽  
Finite Size ◽  
Muonic Hydrogen ◽  
Energy Splitting ◽  
Atomic Systems ◽  
Proton Charge ◽  
Proton Charge Radius ◽  
Rydberg Constant ◽  
Better Than

The long quest for a measurement of the Lamb shift in muonic hydrogen is over. Last year we measured the 2S 1/2F=1 –2P 3/2F=2 energy splitting (Pohl et al., Nature, 466, 213 (2010)) in μp with an experimental accuracy of 15 ppm, twice better than our proposed goal. Using current QED calculations of the fine, hyperfine, QED, and finite size contributions, we obtain a root-mean-square proton charge radius of rp = 0.841 84 (67) fm. This value is 10 times more precise, but 5 standard deviations smaller, than the 2006 CODATA value of rp. The origin of this discrepancy is not known. Our measurement, together with precise measurements of the 1S–2S transition in regular hydrogen and deuterium, gives improved values of the Rydberg constant, R∞ = 10 973 731.568 160 (16) m–1 and the rms charge radius of the deuteron rd = 2.128 09 (31) fm.

scholarly journals ISR Experiment at A1-Collaboration

2019 ◽  
Vol 218 ◽  
pp. 04001 ◽  
Author(s):  
Miha Mihovilovič ◽  
Harald Merkel
Keyword(s):  
Nuclear Physics ◽  
Lamb Shift ◽  
Muonic Hydrogen ◽  
Present Value ◽  
Elastic Peak ◽  
Shift Measurement ◽  
Elastic Line ◽  
Proton Charge ◽  
Proton Charge Radius ◽  
Electromagnetic Processes

The discrepancy between the proton charge radius extracted from the muonic hydrogen Lamb shift measurement and the best present value obtained from the elastic scattering experiments, remains unexplained and represents a burning problem of today’s nuclear physics. In a pursuit of reconciling the puzzle an experiment is underway at MAMI, which exploits the radiative tail of the elastic peak to study the properties of electromagnetic processes and to extract the proton charge form factor $ \left( {\mathop G\nolimits_E^p } \right) $ at extremely small Q2. This paper reports on the latest results of the first such measurement performed at the three-spectrometer facility of the A1-Collaboration, which led to a precise validation of radiative corrections far away from elastic line and provided measurements of $ \mathop G\nolimits_E^p $ for 0.001 ≤ Q2 ≤ 0.017 (GeV/c)2.

Precision spectroscopy of 2S–nP transitions in atomic hydrogen for a new determination of the Rydberg constant and the proton charge radius

2015 ◽  
Vol T165 ◽  
pp. 014030 ◽  
Author(s):  
Axel Beyer ◽  
Lothar Maisenbacher ◽  
Ksenia Khabarova ◽  
Arthur Matveev ◽  
Randolf Pohl ◽  
...  
Keyword(s):  
Charge Radius ◽  
Atomic Hydrogen ◽  
Precision Spectroscopy ◽  
Proton Charge ◽  
Proton Charge Radius ◽  
Rydberg Constant

scholarly journals A small proton charge radius from an electron–proton scattering experiment

Nature ◽  
2019 ◽  
Vol 575 (7781) ◽  
pp. 147-150 ◽  
Author(s):  
W. Xiong ◽  
A. Gasparian ◽  
H. Gao ◽  
D. Dutta ◽  
M. Khandaker ◽  
...  
Keyword(s):  
Charge Radius ◽  
Proton Scattering ◽  
Proton Charge ◽  
Proton Charge Radius ◽  
Scattering Experiment
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