The nuclear charge radius of ¹³C

Area of Science:

• Nuclear physics
• Atomic physics
• Quantum mechanics

Background:

• Nuclear radii are crucial but often inconsistent across measurement techniques.
• Discrepancies like the proton-radius puzzle highlight challenges in nuclear size determination.
• Precision data for light nuclei beyond helium is limited.

Purpose of the Study:

• To measure the root-mean-square (rms) charge radius of the 13C nucleus with high accuracy.
• To compare experimental results with ab initio nuclear structure calculations.
• To address discrepancies in nuclear radius measurements.

Main Methods:

• Laser spectroscopy of 13C4+ ions, measuring hyperfine components of a specific transition.
• Frequency comb referencing for high-precision measurements.
• Comparison with theoretical calculations based on nuclear structure.

Main Results:

• Determined the center-of-gravity of the 23S → 23P fine-structure triplet with <2 MHz accuracy.
• Improved the uncertainty of the 13C charge radius by a factor of 6 compared to electron scattering.
• Observed a 3σ discrepancy between the new measurement and previous muonic atom results.

Conclusions:

• The study provides a highly accurate nuclear charge radius for 13C.
• The results challenge existing nuclear models and experimental data.
• Further investigation is needed to resolve the discrepancy between laser spectroscopy and muonic atom measurements.