The highly anisotropic phase space (known as longitudinal phase space) of multiparticle final states in high energy hh collisions is studied in detail. It is pointed out that the anisotropy of phase space should manifest itself not only in the dramatic difference in magnitude between the average transverse and longitudinal momenta, but also in the anisotropy of dynamical fluctuations in the two directions. It means that the particle distribution in phase space has the property of selfaffine fractal. A method for experimentally testing the selfaffine fractality and measuring its characteristic ...