Constraints on unparticle interactions from invisible decays of Z, quarkonia and neutrinos

Unparticles (U) interact weakly with particles. The direct signature of unparticles will be in the form of missing energy. We study constraints on unparticle interactions using totally invisible decay modes of Z, vector quarkonia V and neutrinos. The constraints on the unparticle interaction scale Lambda(U) are very sensitive to the dimension d(U) of the unparticles. From invisible Z and V decays, we find that with d(U) close to 1 for vector U, the unparticle scale Lambda(U) can be more than 10(4) TeV, and for d(U) around 2, the scale can be lower than one TeV. From invisible neutrino decays, we find that if d(U) is close to 3/2, the scale can be more than the Planck mass, but with d(U) around 2 the scale can be as low as a few hundred GeV. We also study the possibility of using V(Z)->gamma+U to constrain unparticle interactions, and find that present data give weak constraints.