Line shapes in Υ(5S)→B(*
)π with Z(10610) and Z(10650) using effective field theory
The Belle Collaboration recently discovered two resonances, Z b(10610) and Zb(10650) - denoted Zb and Zb′ - in the decays Υ(5S)→Υ(nS)π+π - for n=1, 2, or 3, and Υ(5S)→hb(mP) π+π- for m=1 or 2. These resonances lie very close to the B*B̄ and B*B̄* thresholds, respectively. A recent Belle analysis of the three-body decays Υ(5S)→[B(*)B̄( *)]â̂π± gives further evidence for the existence of these states. In this paper we analyze this decay using an effective theory of B mesons interacting via strong short-range interactions. Some parameters in this theory are constrained using existing data on Υ(5S)→B(*)B̄( *) decays, which requires the inclusion of heavy quark spin symmetry violating operators. We then calculate the differential distribution for Υ(5S)→B(*)B̄(*) π as a function of the invariant mass of the B(*)B ̄(*) pair, obtaining qualitative agreement with experimental data. We also calculate angular distributions in the decay Υ(5S)→Zb(′)π which are sensitive to the molecular character of the Zb(′). © 2013 American Physical Society.
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