$\chi_{QJ} \to\ell^+\ell^-$ within and beyond the Standard Model

TL;DR

This paper calculates the tiny Standard Model predictions for $ ext{chi}_{QJ} o ext{lepton}^+ ext{lepton}^-$ decays and explores potential enhancements in beyond Standard Model theories like 2HDM and Randall-Sundrum models.

Contribution

It provides the first detailed SM predictions for these rare decays and assesses their observability in future experiments, including beyond Standard Model scenarios.

Findings

SM branching ratios are extremely small, making detection challenging.

Enhanced decay rates are possible in 2HDM with large tanβ and Randall-Sundrum models.

Potential observability at LHC but not at BESIII or SuperB.

Abstract

We revisit $\chi_{QJ}\to \ell^+\ell^-$ (with $J=0,1,2$ and $Q=b,c$) within the Standard Model (SM). The electro-magnetic contributions are given in color-singlet model with non-vanishing lepton masses at the leading order of $v$. Numerically, the branching ratios of $\chi_{QJ}\to\ell^{+}\ell^{-}$ predicted within the SM are so small that such decays are barely possible to be detected at future BESIII and SuperB experiments, but may be possible to be observed at the LHC. We investigate $\chi_{b0}\to\ell^+\ell^-$ in Type-II 2HDM with large $\tan\beta$, and $\chi_{b2}\to\ell^+\ell^-$ in the Randall-Sundrum model, to see their chance to be observed in future experiments.