  The ridge particles associated with a near-side jet are identified as medium
partons kicked by the jet near the surface. They carry direct information on
the parton momentum distribution at the moment of jet-parton collisions and the
magnitude of the longitudinal momentum kick. The extracted early parton
momentum distribution has a rapidity plateau structure with a thermal-like
transverse momentum distribution. Such a rapidity plateau structure may arise
from particle production in flux tubes, as color charges and anti-color charges
separate at high energies.
