We find that Epps  hypothesis - namely that the current experimental data set is well represented by a small constant or zero offset from the predictions of Artemyev et al.  - is not supported by standard statistical analysis. We find that adding the new datum recommended by Epp makes the discrepancy that we reported earlier grow with Z even more strongly - rather than weakly, as Epp suggests. Our primary conclusion  of an apparent Z-dependent discrepancy between experiment and theory is unchanged, and is qualitatively novel com- pared to earlier discussion of discrepancies in QED. While Epp suggests that our results extrapolate to problems at very high-Z, we note that our present and previous datasets both include data up to and including Z = 92, and the reduced chi-squared χ2r values showed a negligible discrepancy of the fit over this range of Z.  S. W. Epp, Phys. Rev. Lett. (2013).  A. N. Artemyev, V. M. Shabaev, V. A. Yerokhin, G. Plunien, and G. Soff, Phys Rev A 71, 062104 (2005).  C. T. Chantler, M. N. Kinnane, J. D. Gillaspy, L. T. Hudson, A. T. Payne, L. F. Smale, A. Henins, J. M. Pomeroy, J. N. Tan, J. A. Kimpton, et al., Phys Rev Letts 109, 153001 (2012).
Citation: Physical Review Letters
Pub Type: Journals
x-ray spectroscopy, quantum electrodynamics