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Constraints on proton structure from precision atomic-physics measurements.
Stanley J Brodsky1, Carl E Carlson, John R Hiller
1Stanford Linear Accelerator Center, Stanford University, Stanford, California 94309, USA.
Physical Review Letters
|February 9, 2005
Summary
The Zemach radius, a key proton structure measure, is precisely determined using atomic physics data from hydrogen and muonium. This finding offers crucial constraints for proton form factor measurements from accelerator experiments.
Area of Science:
- Atomic Physics
- Quantum Electrodynamics (QED)
- Particle Physics
Background:
- Ground-state hyperfine splittings in hydrogen and muonium are precisely measured.
- The difference in these splittings, after corrections, is sensitive to proton structure.
Purpose of the Study:
- To determine the Zemach radius, a fundamental measure of proton structure, using atomic physics data.
- To constrain accelerator-based measurements of proton form factors.
- To experimentally extract QED corrections to hydrogenic hyperfine data using muonium.
Main Methods:
- Analysis of ground-state hyperfine splittings in hydrogen and muonium.
- Correction for magnetic moment and reduced mass effects.
- Calculation of the Zemach radius from an integral of proton electric and magnetic form factors.
Main Results:
- The Zemach radius was determined to be (1.019 ± 0.016) fm.
- This atomic physics determination provides tight constraints on fits to proton form factor data from accelerators.
- A significant discrepancy was observed between measured and theoretical QED corrections for hydrogenic hyperfine data, mirroring a positronium anomaly.
Conclusions:
- Atomic physics measurements provide a precise determination of the Zemach radius, a fundamental proton property.
- The results highlight the interplay between atomic physics, QED, and proton structure.
- The observed QED discrepancy warrants further theoretical and experimental investigation.