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

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.

Comments: 12 pages, 1 figure; improved presentation; reported at the International Seminar "Quarks 2010", Kolomna, Russia, June, 6-12, 2010; accepted in Yadernaya Fizika, scheduled for publication in March, 2011, Yad. Fiz. [Phys. At. Nucl.], volume 74, issue 3 (2011)