Interpretation of neutral charm mesons near threshold as unparticles

Understand

The existence of the $X(3872)$ resonance extremely close to the $D^{*0} \bar{D}^0$ threshold implies that neutral charm mesons have an approximate nonrelativistic conformal symmetry.

• Systems consisting of these mesons with small kinetic energies produced in a short-distance reaction are unparticles in the sense that they can be created by operators with definite scaling dimensions in a nonrelativistic conformal field theory.
• There is a scaling region in which their energy distribution has power-law behavior with an exponent determined by the scaling dimension of the operator.
• The unparticle associated with two neutral charm mesons produces a peak in the recoil momentum spectrum of $K^\pm$ in inclusive decays of $B^\pm$ that has been observed.