The Rydberg constant and proton size from atomic hydrogen.

Area of Science:

• Atomic Physics
• Quantum Mechanics
• Particle Physics

Background:

• The proton radius puzzle arises from a significant discrepancy in proton charge radius measurements between regular hydrogen and muonic hydrogen.
• This discrepancy has persisted for years, challenging fundamental physics understanding.

Purpose of the Study:

• To precisely measure the proton charge radius using a novel experimental approach with regular hydrogen.
• To investigate the discrepancy in proton radius measurements and contribute to its resolution.

Main Methods:

• Utilized a cryogenic beam of hydrogen atoms to measure the 2S-4P transition frequency.
• Employed an asymmetric fit function to mitigate line shifts caused by quantum interference.

Main Results:

• Determined the Rydberg constant to be 10973731.568076(96) per meter.
• Measured the proton root-mean-square charge radius (r_p) as 0.8335(95) femtometer.
• The obtained r_p value is 3.3 standard deviations smaller than previous hydrogen data and agrees well with muonic hydrogen measurements.

Conclusions:

• The new hydrogen measurement aligns with muonic hydrogen results, suggesting a smaller proton radius.
• This study provides crucial data that helps resolve the long-standing proton radius puzzle.