New x-ray measurements in Helium-like Atoms increase discrepancy between   experiment and theoretical QED
  A recent 15 parts-per-million (ppm) experiment on muonic hydrogen found a major discrepancy with QED and independent nuclear size determinations. Here we find a significant discrepancy in a different type of exotic atom, a medium-Z nucleus with two electrons. Investigation of the data collected is able to discriminate between available QED formulations and reveals a pattern of discrepancy of almost 6 standard errors of experimental results from the most recent theoretical predictions with a functional dependence proportional to Z^n where n=4. In both the muonic and highly charged systems, the sign of the discrepancy is the same, with the measured transition energy higher than predicted. Some consequences are possible or probable, and some are more speculative. This may give insight into effective nuclear radii, the Rydberg, the fine-structure constant or unexpectedly large QED terms. 
Christopher T. Chantler, Andrew T. Payne, John D. Gillaspy, Lawrence   T. Hudson, Lucas F. Smale, Albert Henins, Justin A. K...
physics.atom-ph hep-ph quant-ph