@8]. In this region the background is large, and some methods to separate the particles in the cone from the background were proposed in [@ag; @dst].

The main difference between the trigger experiments at RHIC and this nontrigger experiment is in the treatment of the rest system of the medium. The influence of the medium motion on cone angles was considered in . It is important because all the above formulas are valid for emission in the rest system of the medium.

At RHIC, the 90$^o$ trigger jet defines the direction of the away-side jet. Because of position of the trigger perpendicular to the collision axis of initial ions, the accompanying partons (particles) feel the medium at rest on the average in the c.m.s. The similar trigger experiments are possible at LHC. It is important to measure the cone angles for different angular positions of the trigger to have an access to different coordinate systems where the target is at rest on the average and to register the medium motion.

In nontrigger experiments, dealing with forward moving high energy partons inside of one of the colliding ions, the rest system of the medium is the rest system of another colliding 