LAUSR

We study the dipion transitions ϒ(4S)→ϒ(nS)π+π-(n=1,2). In particular, we consider the effects of the two intermediate bottomoniumlike exotic states Zb(10610) and Zb(10650) as well as bottom meson loops. The strong pion-pion final-state interactions, especially including channel coupling to KK¯ 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 Zb-exchange terms. For the ϒ(4S)→ϒ(2S)π+π- decay, the result shows that including the effects of the Zb exchange and the bottom meson loops can naturally reproduce the two-hump behavior of the ππ mass spectra. Future angular distribution data are decisive for the identification of different production mechanisms. For the ϒ(4S)→ϒ(1S)π+π- decay, we show that there is a narrow dip around 1 GeV in the ππ invariant mass distribution, caused by the final-state interactions. The distribution is clearly different from that in similar transitions from lower ϒ 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 ϒ(4S)→ϒ(1S)K+K- process.