  We analyze renormalization of the pi band of n-doped epitaxial graphene on
Ir(111) induced by electron-phonon coupling. Our procedure of extracting the
bare band relies on recursive self-consistent refining of the functional form
of the bare-band until the convergence. We demonstrate that the components of
the self-energy, as well as the spectral intensity obtained from angle-resolved
photoelectron spectroscopy (ARPES) show that the renormalization is due to the
coupling to two distinct phonon excitations. From the velocity renormalization
and an increase of the imaginary part of the self-energy we find the
electron-phonon coupling constant to be ~0.2, which is in fair agreement with a
previous study of the same system, despite the notable difference in the width
of spectroscopic curves. Our experimental results also suggest that potassium
intercalated between graphene and Ir(111) does not introduce any additional
increase of the quasiparticle scattering rate.
