On the structure of the pi pi invariant mass spectra of the Upsilon(4S)-->Upsilon(1S,2S) pi^+ pi^- decays

Abstract

We perform a model-independent analysis for recently reported data of the ${\pi }^{+}{\pi }^{-}$ invariant mass spectra in the ${\rm Y}(4S)\to {\rm Y}(1S,2S){\pi }^{+}{\pi }^{-}$ decays and point out that there does exist a broad peak below 0.6 GeV in the data of the ${\rm Y}(4S)\to {\rm Y}(1S){\pi }^{+}{\pi }^{-}$ decay, which is analogous to that in the ${\rm Y}(3S)\to {\rm Y}(1S){\pi }^{+}{\pi }^{-}$ decay. With the data of ${\rm Y}(4S)$ decays, we further test our model developed for studying the puzzle in the ${\rm Y}(3S)\to {\rm Y}(1S){\pi }^{+}{\pi }^{-}$ decay. The result shows that with such a model, all the ${\pi }^{+}{\pi }^{-}$ invariant mass spectra of ${\rm Y}(4S)$ decays can be described. We also predict the $\cos {\theta }_{\pi }^{\ast }$ distributions of ${\rm Y}(4S)\to {\rm Y}(1S,2S){\pi }^{+}{\pi }^{-}$ decays, which can be used to justify our model prediction.

Comments: 11 pages, 5 figures. Extended to include new data; title changed. Version accepted for publication in Phys. Lett. B