The Z\to c\bar c\to\gamma \gamma^{\ast}, Z\to b\bar b\to\gamma \gamma^{\ast} triangle diagrams and the Z\to\gamma \psi, Z\to \gamma \Upsilon decays

TL;DR

This paper develops a sum rule approach to study Z boson decays into a photon and heavy quarkonium states, calculating branching ratios and discussing potential measurements at the LHC.

Contribution

It introduces a novel sum rule method for analyzing Z decay amplitudes into heavy quarkonia and provides quantitative predictions for branching ratios.

Findings

Lower bounds for BR(Z→γψ) and BR(Z→γΥ) are established.

Predicted BRs could reach around 10^{-6} and be measurable at LHC.

Angle distributions in decays are also calculated.

Abstract

It is expounded the approach to the Z\to\gamma\Psi and Z\to\gamma\Upsilon decay study, based on the sum rules for the Z\to c\bar c\to\gamma\gamma^{\ast} and Z\to b\bar b\to\gamma\gamma^{\ast} amplitudes and their derivatives. The branching ratios of the Z\to\gamma\psi and Z\to\gamma\Upsilon decays are calculated for different guesses as to saturation of the sum rules. The lower bounds of \sum_{\psi} BR(Z\to\gamma\psi) = 1.95\cdot 10^{-7} and \sum_{\Upsilon} BR(Z\to\gamma\Upsilon) = 7.23\cdot 10^{-7} are found. Deviations from the lower bounds are discussed, among them the possibility of BR(Z\to\gamma J/\psi(1S))\sim BR(Z\to\gamma\Upsilon(1S))\sim 10^{-6}, that could be probably measured in LHC. The angle distributions in the Z\to\gamma\psi and Z\to\gamma\Upsilon decays are calculated also.