The decay of resonance in the Lobachevsky velocity space is represented by an isosceles triangle inscribed in a horocycle. Near the decay triangles of scalar, strange mesons and Δ, N baryons, there are Heron’s triangles, for which are equal to integers: a) the length of the arc of the oricycle subtending the base, by the cotangent of half the angle at the vertex opposite the base; b) the hyperbolic cosines of the lengths of the lateral sides and the lengths of the bases.

Heron’s Triangles and Resonance Decays in Lobachevsky Velocity Space