Effects of $Z_b$ states and bottom meson loops on ${\rm Y}(4S)\to {\rm Y}(1S,2S){\pi }^{+}{\pi }^{-}$ transitions

Abstract

We study the dipion transitions ${\rm Y}(4S)\to {\rm Y}(nS){\pi }^{+}{\pi }^{-}$ $(n=1,2)$. In particular, we consider the effects of the two intermediate bottomoniumlike exotic states $Z_b(10610)$ and $Z_b(10650)$ as well as bottom meson loops. The strong pion-pion final-state interactions, especially including channel coupling to $K\bar{K}$ in the $S$-wave, are taken into account model-independently by using dispersion theory. Based on a nonrelativistic effective field theory we find that the contribution from the bottom meson loops is comparable to those from the chiral contact terms and the $Z_b$-exchange terms. For the ${\rm Y}(4S)\to {\rm Y}(2S){\pi }^{+}{\pi }^{-}$ decay, the result shows that including the effects of the $Z_b$-exchange and the bottom meson loops can naturally reproduce the two-hump behavior of the $\pi \pi$ mass spectra. Future angular distribution data are decisive for the identification of different production mechanisms. For the ${\rm Y}(4S)\to {\rm Y}(1S){\pi }^{+}{\pi }^{-}$ decay, we show that there is a narrow dip around 1 GeV in the $\pi \pi$ invariant mass distribution, caused by the final-state interactions. The distribution is clearly different from that in similar transitions from lower ${\rm Y}$ states, and needs to be verified by future data with high statistics. Also we predict the decay width and the dikaon mass distribution of the ${\rm Y}(4S)\to {\rm Y}(1S)K^{+}{K}^{-}$ process.

25 pages, 8 figures, predictions of the decay width and the dikaon mass distribution of the ${\rm Y}(4S)\to {\rm Y}(1S)K^{+}{K}^{-}$ process added, more discussions added

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Cited by in corpus (6)

• Pentaquark and Tetraquark states
• Nature of the $Y(4260)$: A light-quark perspective
• Insights into $Z_b(10610)$ and $Z_b(10650)$ from dipion transitions from ${\rm Y}(10860)$
• Study of $\eta$ and dipion transitions in ${\rm Y}(4S)$ decays to lower bottomonia
• Weak Decays of Triply Heavy Tetraquarks $b\bar{c}b\bar{q}$
• $D$ wave bottomonia production from $Z_b^{(\prime )}$ decay