and 
. Both the ridge-like near-side and
the double-hump away-side structures were obtained. However, the
mechanism of ridge production was not clear. In order to
understand it, we study a simple model with only one high-energy
density peripheral tube in a smooth cylindrical back-ground, with
longitudinal boost invariance. The results are rather surprising,
but the model does produce the triple-ridge structure with one
high ridge plus two lower ones placed symmetrically with respect
to the former one. The shape of this structure is rather stable in
a wide range of parameters.
Key words: two-particle correlations, ridge effect, hydrodynamic model
