Double Charmonia Production in Exclusive $Z$ Boson Decays

TL;DR

This paper analyzes double charmonium production in exclusive Z boson decays using NRQCD and light-cone models, providing theoretical predictions for branching fractions and examining effects of internal quark motion and helicity suppression.

Contribution

It offers a systematic comparison of NRQCD and light-cone models for Z boson decays into double charmonia, including new predictions for branching fractions.

Findings

Internal quark motion increases branching fractions by 1.5 times in allowed processes.

Light-cone predictions are zero for forbidden reactions, while NRQCD predicts small but non-zero values.

Helicity suppression influences the production rates significantly.

Abstract

This article is devoted to systematic analysis of double charmonium production in exclusive $Z$ boson decays in the framework of Nonrelativistic Quantum Chromodynamic (NRQCD) and leading twist light-cone (LC) models. Theoretical predictions for branching fractions of all considered decays are presented. According to obtained results in the case of allowed by helicity suppression rule processes the effect of internal quark motion increases the branching fraction by a factor 1.5, while for forbidden reactions LC predictions are strictly zero, while NRQCD ones are significantly smaller than for allowed.