can be verified by measuring the angular distribution of the lepton pairs with different masses. The trigger-jet experiments similar to that at RHIC are necessary to check this prediction. One should measure the angles between the companion jet axis and the total momentum of the lepton pair. The Cherenkov pairs with masses between 0.4 GeV and 0.7 GeV should tend to fill in the rings around the jet axis. The angular radius $\theta $ of the ring is determined by the usual condition (\[cos\]).

Another way to demonstrate it is to measure the average mass of lepton pairs as a function of their polar emission angle (pseudorapidity) with the companion jet direction chosen as $z$-axis. Some excess of low-mass pairs may be observed at the angle (\[cos\]).

In practice, these procedures can be quite complicated at comparatively low energies if the momenta of decay products are comparable to the transverse momentum of the resonance. It can be a hard task to pair leptons in reliable combinations. The Monte Carlo models could be of some help.

In non-trigger experiments like that of NA60 there is another obstacle. Everything is averaged over directions of initial partons. Different partons are moving in different 