# Predictions of $\Upsilon(4S) \to h_b(1P,2P) \pi^+\pi^-$ transitions

## TL;DR

This paper investigates the mechanisms behind certain bottomonium transitions, predicting branching ratios influenced by intermediate states and loops, with implications for understanding heavy quark spin flip processes.

## Contribution

It introduces a detailed analysis of bottom meson loops and $Z_b$-exchange contributions in $S$ transitions, providing new predictions for branching ratios and the relative importance of these mechanisms.

## Key findings

- Bottom meson loops dominate over $Z_b$-exchange in $S o h_b(1P)\pi\pi$ transitions.
- Predicted branching ratios vary significantly depending on interference effects.
- Bottom meson loops are insufficient to explain decay rates of $S$ to $S$ states.

## Abstract

In this work, we study the contributions of the intermediate bottomoniumlike $Z_b$ states and the bottom meson loops in the heavy quark spin flip transitions $\Upsilon(4S) \to h_b(1P,2P) \pi^+\pi^-$. Depending on the constructive or destructive interferences between the $Z_b$-exchange and the bottom meson loops mechanisms, we predict two possible branching ratios for each process: BR$_{\Upsilon(4S) \to h_b(1P)\pi^+\pi^-}\simeq\big(1.2^{+0.8}_{-0.4}\times10^{-6}\big)$ or $\big( 0.5^{+0.5}_{-0.2}\times10^{-6}\big)$, and BR$_{\Upsilon(4S) \to h_b(2P)\pi^+\pi^-}\simeq \big(7.1^{+1.7}_{-1.1}\times10^{-10}\big)$ or $\big( 2.4^{+0.2}_{-0.1}\times10^{-10}\big)$. The bottom meson loops contribution is found to be much larger than the $Z_b$-exchange contribution in the $\Upsilon(4S) \to h_b(1P) \pi\pi$ transitions, while it can not produce decay rates comparable to the heavy quark spin conserved $\Upsilon(4S) \to \Upsilon(1S,2S) \pi\pi$ processes. We also predict the branch fractions of $\psi(3S,4S) \to h_c(1P)\pi^+\pi^-$ contributed from the charm meson loops.