ion. Therefore the cone angle should be calculated in that system and then transformed to the c.m.s. That is why these angles are so large even at small values of the refractivity index for high energy gluons. The low energy Cherenkov gluons emitted at rather large angles in the rest system of this nucleus are hard to observe because at LHC they fly backward inside the accelerator pipe (with $\vert y\vert \approx 8$, i.e. close to 180$^o$ in c.m.s.).

The idea about Cherenkov gluons was first used to interpret the cosmic ray event at energy 10$^{16}$ eV [@1; @23] where two rings more densely populated by particles than their surroundings were noticed. It is demonstrated in Fig. 3 where the number of produced particles is plotted as a function of the distance from the collision point. It clearly shows two maxima. They correspond to two maxima on the pseudorapidity scale which would arise due to two rings produced. Again, the medium rest system coincides with the target rest system.

This event has been registered in the detector with nuclear and X-ray emulsions during the balloon flight at the altitude about 30 km. The most indefinite characteristics of the event is 