Abstract
The experimental line shapes available in the B$ \bar {B} $*, B*$ \bar {B} $*, hb(1P)π and hb(2P)π channels are analysed using a theoretical EFT-based framework manifestly consistent with unitarity and analyticity. The line shapes are calculated using a system of coupled channel integral equations with the potential consisting of the one-pion and one-eta meson exchange interactions from the lightest Goldstone boson octet as well as of several contact terms at leading and subleading orders which are adjusted to minimise the overall chi squared. The pole positions of the Zb(10610) and Zb(10650) are extracted for the best fits corresponding to χ2/d.o.f. of the order of one.
Highlights
The discovery of the two charged resonances Zb+(10610) and Zb+(10650) by the Belle Collaboration [1] gave evidence of an exotic nature of these bottomonium-like states
In this contribution we provide a brief summary of an effective field theory (EFT) approach to the Zb(10610) and Zb(10650) developed in Ref. [9] and used to analyse the experimental data in various elastic and inelastic channels
All low-energy constants were fixed from a combined fit to the experimental line shapes in the decays Υ(10860) → BB∗π, B∗B∗π, hb(1P)ππ, and hb(2P)ππ which proceed via the excitation of the Zb(10610) and Zb(10650) exotic states as well as from the total rates for the decays Υ(10860) → Υ(nS )ππ (n = 1, 2, 3)
Summary
The discovery of the two charged resonances Zb+(10610) and Zb+(10650) by the Belle Collaboration [1] gave evidence of an exotic nature of these bottomonium-like states. The proximity of the Zb and Zb to the BB∗/B∗Band B∗B∗ thresholds, respectively, together with the fact that these open-flavour hadronic channels are by far the dominant (S-wave) decay channels of these states is regarded as a strong evidence for a molecular nature of the Zb’s [5,6,7]; for an alternative scenario within the tetraquark picture see, e.g., a review [8] In this contribution we provide a brief summary of an effective field theory (EFT) approach to the Zb(10610) and Zb(10650) developed in Ref. In a recent work [10], the same EFT approach was applied to predict in a parameter-free way the pole positions and the line shapes of the spin partners of the Zb states
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