$Z_b/Z_b^{\prime }\to {\rm Y}\pi$ and $h_b\pi$ decays in intermediate meson loops model

Abstract

With the recent measurement of $Z_b(10610)$ and $Z_b(10650)\to B{\bar{B}}^{\ast }+c.c.$ and $B^{\ast }{\bar{B}}^{\ast }$, we investigate the transitions from the $Z_b(10610)$ and $Z_b(10650)$ to bottomonium states with emission of a pion via intermediate $B{B}^{\ast }$ meson loops. The experimental data can be reproduced in this approach with a commonly accepted range of values for the form factor cutoff parameter $\alpha$. The ${\rm Y}(3S)\pi$ decay channels appear to experience obvious threshold effects which can be understood by the property of the loop integrals. By investigating the $\alpha$-dependence of partial decay widths and ratios between different decay channels, we show that the intermediate $B{B}^{\ast }$ meson loops are crucial for driving the transitions of $Z_b/Z_b^{\prime }\to {\rm Y}(nS)\pi$ with $n=1,2,3$, and $h_b(mP)\pi$ with $m=1$ and 2.

Comments: 9 pages, 5 figures