Penning-Trap Mass Measurement of Helium-4.

Area of Science:

• Atomic Physics
• Metrology
• Nuclear Physics

Background:

• Precise atomic mass measurements are fundamental for testing physical theories and establishing fundamental constants.
• Previous measurements of helium-4's atomic mass have reached high precision but may contain discrepancies.

Purpose of the Study:

• To determine the atomic mass of helium-4 ($^{4}$He) with unprecedented precision.
• To provide an independent, high-accuracy value for $^{4}$He atomic mass for comparison with existing data and theoretical predictions.

Main Methods:

• Utilized the Light-ion trap (LIONTRAP) facility, a high-precision Penning-trap mass spectrometer.
• Measured the mass of the $^{4}$He$^{2+}$ ion to a precision of 12 parts-per-trillion.
• Calculated the neutral $^{4}$He atomic mass from the ion mass measurement.

Main Results:

• Reported a measurement of the $^{4}$He$^{2+}$ ion mass: m($^{4}$He$^{2+}$)=4.001506179651(48) u.
• Determined the atomic mass of neutral $^{4}$He: m($^{4}$He)=4.002603254653(48) u.
• The new measurement is slightly more precise than the CODATA18 value.

Conclusions:

• The determined atomic mass of $^{4}$He deviates from the CODATA18 value by 6.6 standard deviations.
• This significant deviation necessitates further investigation and may indicate a need to re-evaluate current atomic mass data or theoretical models.
• The high precision achieved highlights the capabilities of the LIONTRAP facility for fundamental constant measurements.