Empirical determination of the Bohr-Weisskopf effect in cesium and improved tests of precision atomic theory in searches for new physics

Understand

The finite distribution of the nuclear magnetic moment across the nucleus gives a contribution to the hyperfine structure known as the Bohr-Weisskopf (BW) effect.

• We have obtained an empirical value of -0.24(18)% for this effect in the ground and excited s states of atomic Cs-133.
• This value is found from historical muonic-atom measurements in combination with our muonic-atom and atomic many-body calculations.
• The effect differs by 0.5% in the hyperfine structure from the value found using the uniform magnetization distribution, which has been commonly employed in the precision heavy-atom community over the last several decades.