  The near-side depression in two-proton or two-antiproton azimuthal
correlations in $pp$ collisions at $\sqrt{s}=$7 TeV has been observed
experimentally and then qualitatively reproduced in our earlier studies with a
multi-phase transport model. In this study, we further investigate the origin
of the depression feature in two-baryon correlations in small collision
systems. We find that the initial parton-level spatial correlation, a finite
expansion in the parton stage, and quark coalescence are important ingredients
leading to the near-side depression. In particular, we find that a finite
expansion of the parton system leads to a finite space-momentum correlation at
hadronization, which then converts the near-side depression in the coordinate
space to that in the momentum space. These results suggest that a partonic
matter with a finite lifetime is formed in the pp collisions. Further studies
are needed to determine whether the partonic matter is near local equilibrium
and can thus be called a QGP or far away from local equilibrium.
