Zb tetraquark channel and $B\bar B^*$ interaction from lattice QCD

TL;DR

This study uses lattice QCD to investigate the interaction between B and B* mesons, providing evidence for a bound state that could explain the experimentally observed Zb(10610) tetraquark candidate.

Contribution

It presents a lattice QCD analysis of the B B* interaction in the static b-quark approximation, revealing a potential bound state near the experimental Zb(10610).

Findings

Evidence of a B B* bound state below threshold.

Significant attraction in the B B* channel.

Potential explanation for Zb(10610) as a molecular state.

Abstract

Two tetraquark candidates $Z_b(10610)$ and $Z_b(10650)$ with flavor structure $\bar bb\bar du$ were discovered by Belle experiment in 2011. We present a preliminary $N_f=2$ lattice study of the $\bar bb\bar du$ 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 $\bar b$. The lower eigenstates are related to a bottomonium and a pion. One of the higher eigenstates is dominated by $B\bar B^*$: its energy is significantly below $m_B+m_{B*}$ for r=[0.1,0.4] fm, which suggests sizable attraction. The attractive potential $V(r)$ between $B$ and $\bar B^*$ is extracted assuming that this eigenstate is related exclusively to $B\bar B^*$. Assuming a certain form of the potential and solving non-relativistic Schrodinger equation, we find a bound state pole below $B\bar B^*$ threshold. For certain parametrizations, the bound state is very close to the $B\bar B^*$ threshold - this feature could be related to $Z_b(10610)$ in the experiment.