$Z_b(10610)$ and $Z_b(10650)$ structures produced by the initial single pion emission in the ${\rm Y}(5S)$ decays

Abstract

We propose an unique mechanism called {\it Initial Single Pion Emission} existing in the ${\rm Y}(5S)$ decays, and further study the line shapes of $d\Gamma ({\rm Y}(5S\to {\rm Y}(nS){\pi }^{+}{\pi }^{-}))/d{m}_{{\rm Y}(nS){\pi }^{+}}$ ($n=1,2,3$) and $d\Gamma ({\rm Y}(5S\to h_b(mP){\pi }^{+}{\pi }^{-}))/d{m}_{h_b(mP){\pi }^{+}}$ ($m=1,2$). We find sharp structures around 10610 MeV and 10650 MeV in the obtained theoretical line shapes of $d\Gamma ({\rm Y}(5S\to {\rm Y}(nS){\pi }^{+}{\pi }^{-}))/d{m}_{{\rm Y}(nS){\pi }^{+}}$ and $d\Gamma ({\rm Y}(5S\to h_b(mP){\pi }^{+}{\pi }^{-}))/d{m}_{h_b(mP){\pi }^{+}}$ distributions, which could naturally correspond to the $Z_b(10610)$ and $Z_b(10650)$ structures newly observed by Belle.

Comments: 5 pages, 4 figures. More discussions added. Accepted by Phys. Rev. D