Exotic molecular states in the decays of vector bottomonia

V Baru,A A Filin,Q Wang,E Epelbaum,C Hanhart,A V Nefediev

doi:10.1051/epjconf/201921202002

Abstract

The most recent experimental data for the decays of the vector bottomonium γ(10860) proceeding through the formation of the states Zb(10610) and Zb(10650) are analysed simultaneously using solutions of the Lippmann-Schwinger equations which respect constraints from unitarity and analyticity. The interaction potential in the open-bottom channels $ {B^{(*)}}{\bar B^*} $ contains short-range interactions as well as the one-pion exchange; both types of the interaction are taken into account fully nonperturbatively. This way, all parameters of the interaction are fixed directly from the data and the pole positions for the Zb’s are determined as a prediction. In particular, both Zb states are found to be described by resonance poles located on the unphysical Riemann sheets in the vicinity of the corresponding thresholds. The heavy quark spin symmetry (HQSS) is employed to predict, in a parameter-free way, the pole positions and the line shapes in the elastic and inelastic channels for the Zbs’ spin partner states WbJ with the quantum numbers J++ (J = 0, 1, 2). Such spin partners can be produced in radiative decays of the vector bottomonium Υ(10860) and are expected to be detected in the Belle-II experiment.

Highlights

In the last fifteen years many states in the spectrum of charmonium and bottomonium were discovered experimentally, and while some of them can be well described by the quark model, others can not
The heavy quark spin symmetry (HQSS) is employed to predict, in a parameter-free way, the pole positions and the line shapes in the elastic and inelastic channels for the Zbs’ spin partner states WbJ with the quantum numbers J++ (J = 0, 1, 2). Such spin partners can be produced in radiative decays of the vector bottomonium Υ(10860) and are expected to be detected in the Belle-II experiment
Following work [7], we promote the S -to-D O(p2) contact term (CT) from NLO to LO, that improves renormalisability of the theory and, in addition, we include the S -to-S O(p2) contact term explicitly, that is, we build an almost complete NLO, up to corrections from the long-range two-pion exchange (TPE) which does not follow from the iterations of the one-pion exchange (OPE)

Summary

Introduction

In the last fifteen years many states in the spectrum of charmonium and bottomonium were discovered experimentally, and while some of them can be well described by the quark model, others can not. Charged 1+− states Zb(10610) and Zb(10650) in the spectrum of bottomonium were observed by the Belle Collaboration in 2011 [2] Parameters of these states (MZb = 10607.2 ± 2.0 MeV, ΓZb = 18.4 ± 2.4 MeV, MZb = 10652.2 ± 1.5 MeV, ΓZb = 11.5 ± 2.2 MeV [3]) demonstrate that they reside close to the BB∗ and B∗B∗ threshold, respectively. Proximity of open-flavour thresholds implies a large admixture of the meson-meson component in the wave function of the resonance, so that it becomes a strong candidate for a molecular state. It remains an open question whether the resonance is a bound or virtual state, or it can be described as an above-threshold resonance or a coupled-channel pole.

Building a common EFT for the Zb’s and WbJ’s

Data analysis for the Zb’s

Predictions for the WbJ’s

Conclusions