The Z → cc? → γγ*, Z → bb? → γγ* triangle diagrams and the Z → γψ, Z → γγ decays

摘要

We expounded an approach for studying the Z → γψ and Z → γγ decay based on the sum rules for the Z → cc? → γγ~* and Z → bb? → γγ~* amplitudes and their derivatives. We calculate the branching ratios of the Z → γψ and Z → γγ decays under different suppositions about the saturation of the sum rules. We find the lower bounds of Σ _ψ BR(Z → γψ) = 1.95 · 10 ~(-7) and Σ _γ BR(Z → γγ) = 7.23 · 10 ~(-7) and discuss deviations from the lower bounds including the possibility of BR[Z → γJ/ψ(1S)] ~ BR[Z → γγ(1S)] ~ 10 ~(-6), which is probably measurable at the LHC. Moreover, we calculate the angle distributions in the Z → γψ and Z → γγ decays.