The modern name is also indicated, the beta function, introduced by C. Callan and K. Symanzik in 1970. Since it is a mere function of g, integration in g of a perturbative estimate of it permits specification of the renormalization trajectory of the coupling, that is, its variation with energy, effectively the function G in this perturbative approximation. The renormalization group prediction (cf. Stueckelberg–Petermann and Gell-Mann–Low works) was confirmed 40 years later at the LEP accelerator experiments: the fine structure "constant" of QED was measured to be about 1 ⁄ 127 at energies close to 200 GeV, as opposed to the standard low-energy physics value of 1 ⁄ 137 .