  A parton produced with a high transverse momentum in a hard collision is
regenerating its color field, intensively radiating gluons and losing energy.
This process cannot last long, if it ends up with production of a leading
hadron carrying the main fraction z_h of the initial parton momentum. So energy
conservation imposes severe constraints on the length scale of production of a
single hadron with high pT. As a result, the main reason for hadron quenching
observed in heavy ion collisions, is not energy loss, but attenuation of the
produced colorless dipole in the created dense medium. The latter mechanism,
calculated with the path-integral method, explains well the observed
suppression of light hadrons and the elliptic flow in a wide range of energies,
from the lowest energy of RHIC up to LHC, and in a wide range of transverse
momenta. The values of the transport coefficient extracted from data range
within 1-2 GeV^2/fm, dependent on energy, and agree well with the theoretical
expectations.
