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

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