A Determination of the Fine Structure Constant Using Precision Measurements of Helium Fine Structure

Aug 10, 2010, 1:00 pm2:00 pm
Jadwin 303


Event Description

Recently published theoretical predictions by Pachucki and Yerokhin are in good agreement with the most precise measurements of helium fine structure and, for the first time, represent a complete calculation up to and including terms of order mα7. In addition to serving as a test of this theory, more precise measurements could also yield a new determination of the fine structure constant α using atomic fine structure. A determination of α using helium fine structure was originally suggested by Charles Schwartz in a 1964 paper as a possible successor to the hydrogen determination. However, first the Josephson Effect and subsequently other methods superseded this approach, and only now can we again realize a competitive value for α using atomic fine structure. For my work, spectroscopic measurements of the helium atom are performed to high precision using an atomic beam apparatus and electro-optic laser techniques. With this setup, I have measured to 10 ppb the J = 0 to J = 2 fine structure interval in the 23P state of 4He, yielding a precision to better than 5 ppb in α. Outside the electron g factor determination, this is comparable in precision to the best alternative determinations of α obtained from photon recoil measurements in both Rb and Cs.