 It contains the full information about the renormalization of the electronic dispersion due to interactions, and the lifetime of the hole created by the excitation.Both can be determined experimentally from the analysis of high-resolution ARPES spectra, under a few reasonable assumptions.Namely, one can assume that the formula_61 part of the spectrum is nearly constant along high-symmetry directions in momentum space, and that the only variable part comes from the spectral function, which in terms formula_72, where the two components of formula_72 are usually taken to be only dependent on formula_74, reads

This function is known from ARPES as a scan along a chosen direction in momentum space, and is a two-dimensional map of the form formula_76.