Revisiting the Helium Isotope-Shift Puzzle with Improved Uncertainties from Nuclear Structure Corrections.

Area of Science:

• Nuclear Physics
• Atomic Physics
• Quantum Chemistry

Background:

• Longstanding tensions exist in measurements of the difference between the squared charge radii of the helion (3He nucleus) and the alpha particle (4He nucleus).
• A significant 3.6σ discrepancy has been observed between extractions from ordinary atoms and muonic atoms.
• This discrepancy, known as the helium isotope-shift puzzle, has been a focus of recent research.

Purpose of the Study:

• To present a novel analysis of uncertainties in nuclear structure corrections required for extracting the difference in radii from spectroscopic experiments.
• To quantify uncertainties arising from the truncation of the chiral effective field theory expansion of the nuclear force.
• To investigate the impact of these uncertainties on the helium isotope-shift puzzle in both muonic and ordinary atoms.

Main Methods:

• Utilized modern Bayesian inference techniques to quantify theoretical uncertainties.
• Analyzed nuclear structure corrections within the framework of chiral effective field theory.
• Applied the analysis to both muonic and ordinary atomic spectroscopy data for helium isotopes.

Main Results:

• The novel analysis of nuclear structure corrections did not resolve the helium isotope-shift puzzle.
• Instead, the discrepancy was reinforced to a 4σ level with the new theoretical input.
• Quantified uncertainties stemming from the truncation of the chiral effective field theory expansion.

Conclusions:

• The helium isotope-shift puzzle persists and is strengthened by a more rigorous theoretical uncertainty quantification.
• Theoretical uncertainties in nuclear structure corrections play a crucial role in interpreting spectroscopic measurements.
• Further theoretical and experimental advancements are needed to fully understand the observed discrepancy in helium nuclear charge radii.