Ridge structure in the Δφ-Δη correlation function associated with a near-side jet

In the Delta phi-Delta eta correlation associated with a near-side jet observed by the STAR Collaboration in heavy-ion collisions at the BNL Relativistic Heavy Ion Collider (RHIC), the ridge structure can be explained by the momentum kick model in which the ridge particles are identified as medium partons which suffer a collision with the jet and acquire a momentum kick along the jet direction. If this is indeed the correct mechanism, the ridge structure associated with the near-side jet may be used to probe the parton momentum distribution at the moment of the jet-parton collision, leading to the result that at that instant the parton temperature is slightly higher and the rapidity width substantially greater than corresponding quantities of their evolution product inclusive particles at the end point of the nucleus-nucleus collision.