  X (3872) because of its mass that is just below D^0 D-^0* threshold and its
quantum number j^pc=1^++ can be considered as a weakly bound molecule. It can
be regarded as a non-relativistic system depicting universality and
compositeness. Physical observables are called universal if they are
insensitive to the range and other details of short-range interaction. Weinberg
introduced compositeness criterion to classify a two-body composite system as
the sum, with different weights, of a compact core and two distinct parts.
