Physical evidence for a new symmetry axis of electromagnetic beams

The new symmetry axis of a well-behaved electromagnetic beam observed in a previous paper [Phys. Rev. A 78, 063831 (2008)] is not purely a mathematical concept. The experimental data reported by Hosten and Kwiat [Science 319, 787 (2008)] are shown to demonstrate the existence of such a symmetry axis that is neither perpendicular nor parallel to the propagation axis. Specifically, it is shown that the idea of this symmetry axis was implicitly used by Hosten and Kwiat in their calculations and exists in their results.