Z_b(10610) and Z_b(10650) decays to bottomonium plus pion

TL;DR

This paper analyzes the decay processes of the $Z_b(10610)$ and $Z_b(10650)$ resonances into bottomonium states plus a pion, using a molecular model and QCD multipole expansion, and compares predictions with experimental data.

Contribution

It introduces a molecular model for $Z_b$ resonances and applies QCD multipole expansion to calculate decay rate ratios, aligning theory with recent experiments.

Findings

Calculated decay rate ratios agree with experimental data.

Supported the molecular interpretation of $Z_b$ resonances.

Provided theoretical estimates for bottomonium decay channels.

Abstract

We consider the transitions from the $Z_b(10610)$ and $Z_b(10650)$ resonances to the states of bottomonium with emission of a pion. The $Z_b$ resonances are viewed as `molecular' objects of a large spatial size made of heavy $B^{(*)}$ mesons, while the states of bottomonium are considered to be compact, so that an application of the leading (dipole) term in the QCD multipole expansion is assumed to be justified. In this way we calculate the ratios of the decay rates to the final states $\Upsilon(nS)\, \pi$ with $n=1,2,3$, and the ratio of the decay rates to $h_b(kP)\, \pi$ with $k=1$ and 2. We find our estimates in a reasonable agreement with recent experimental data.