Evidence of Two-Source King Plot Nonlinearity in Spectroscopic Search for New Boson.

Area of Science:

• Atomic physics
• Nuclear physics
• Beyond Standard Model physics

Background:

• Isotope shifts in atomic spectroscopy probe nuclear properties and fundamental physics.
• Highly forbidden transitions offer unique sensitivity to subtle effects.

Purpose of the Study:

• To measure isotope shifts in ytterbium (Yb) ions using a forbidden octupole transition.
• To test for new fundamental forces and probe nuclear structure.
• To investigate King plot nonlinearity in Yb isotopes.

Main Methods:

• Optical precision spectroscopy of trapped ^{168,170,172,174,176}Yb ions.
• Measurement of the ^{2}S_{1/2}→^{2}F_{7/2} octupole transition.
• Analysis of isotope shift data in conjunction with Yb and Yb+ measurements.

Main Results:

• Observed a King plot nonlinearity of up to 240 standard deviations.
• Experimental data trends are consistent with nuclear density functional theory (Fayans functional).
• A second distinct source of nonlinearity was identified with 4.3 standard deviations confidence.

Conclusions:

• The observed nonlinearity provides strong evidence for physics beyond the Standard Model or novel nuclear phenomena.
• Nuclear density functional theory successfully explains the observed trends.
• The potential second source of nonlinearity warrants further investigation.