Prof. David Toback (Texas A & M University (US))Dr Homer Wolfe (Ohio State University (US)) Jonathan Wilson (University of Michigan)
We report the most sensitive search to date for forbidden and exotic decays of the Z boson to a pair of photons, a pair of neutral mesons, or a neutral meson and a photon. The search is using the full CDF dataset corresponding to 10.0/fb of integrated luminosity. The two decay products are reconstructed in the electromagnetic calorimeter, spanning a rapidity range of |η| < 1.1, and their momenta are used to reconstruct the invariant mass of the pair that is used to identify Z bosons. Bayesian 95% C.L. limits on the signal branching ratio are derived by fitting the signal and background expectations to the data in the Z-mass window of [80,102] GeV/c^2, using a binned likelihood based on the mass distribution. The observed branching ratio limits presented here are 1.66 × 10^-5 for Z->γγ, 2.28 × 10^-5 for Z->π0γ, and 1.73 × 10^-5 for Z->π0π0. The Z->γγ and Z->π0γ limits are more sensitive by factors of 3.1 and 2.3, respectively, than the most stringent Particle Data Group limits reported by experiments at the LEP collider. The Z->π0π0 branching ratio limit is the first limit reported in this decay mode.