Zb tetraquark channel and BB¯? interaction

Abstract

Two tetraquark candidates Zb(10610) and Zb(10650) with flavor structure bb ¯ du ¯ were discovered by Belle experiment in 2011. We present a preliminary Nf = 2 lattice study of the bb ¯ du ¯ system in the approximation of static b quarks, where the total spin of heavy quarks is fixed to one. The ground and the excited eigen-energies are determined as a function of separation r between b and b¯. The lower eigenstates are related to a bottomonium and a pion. One of the higher eigenstates is dominated by BB¯?: its energy is significantly below mB + mB? for r=[0.1,0.4] fm, which suggests sizable attraction. The attractive potential V(r) between B and B¯? is extracted assuming that this eigenstate is related exclusively to BB¯?. Assuming a certain form of the potential at small r < 0.1 fm and solving non-relativistic Schrodinger equation, we find a virtual bound state pole 32?+295 MeV below BB¯? threshold. This pole leads to a narrow peak in the cross-section just above threshold that could be perhaps related to experimental Zb resonances. Given all these approximations, we surprisingly find also a deep bound state 403 ±70 MeV below BB¯? threshold. If such a Zb state exists, it could be experimentally searched in the accurate dependence of rates on ?(1S)?+ invariant mass. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0).