  Studying the nodal quasiparticles in superconducting cuprates by
photoemission with highly improved momentum resolution, we show that a new
"kink" feature in the scattering rate is a key to uncover the nature of
electron correlations in these compounds. Our data provide evidence that the
main doping independent contribution to the scattering can be well understood
in terms of the conventional Fermi liquid model, while the additional doping
dependent contribution has a magnetic origin. This sheds doubt on applicability
of a phonon-mediated pairing mechanism to high temperature superconductors.
