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The size of the proton
Randolf Pohl1, Aldo Antognini, François Nez
1Max-Planck-Institut für Quantenoptik, 85748 Garching, Germany. randolf.pohl@mpq.mpg.de
Nature
|July 9, 2010
Summary
Researchers measured the proton
Area of Science:
- Atomic and Molecular Physics
- Quantum Electrodynamics (QED)
- Particle Physics
Background:
- The proton's properties, like its charge radius, are not fully understood.
- Existing measurements of the proton charge radius have limitations in accuracy.
- Accurate proton radius measurements are crucial for testing fundamental physics theories.
Purpose of the Study:
- To improve the accuracy of the proton charge radius measurement.
- To investigate discrepancies between different measurement methods.
- To test the validity of quantum electrodynamics (QED) calculations.
Main Methods:
- Utilized pulsed laser spectroscopy on muonic hydrogen.
- Measured the muonic Lamb shift with high precision.
- Calculated the proton charge radius based on the measured Lamb shift and theoretical models.
Main Results:
- Determined a new value for the proton charge radius: r(p) = 0.84184(67) fm.
- This value differs by 5.0 standard deviations from the current CODATA value.
- The findings suggest potential issues with QED calculations or the Rydberg constant.
Conclusions:
- The new proton charge radius measurement challenges existing values.
- Discrepancies may necessitate revisions in QED calculations or fundamental constants.
- Further research is needed to resolve the observed differences.
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