Lattice Prediction for Deeply Bound Doubly Heavy Tetraquarks

TL;DR

This study uses lattice QCD to predict the existence of stable doubly heavy tetraquarks with bottom quarks, providing evidence for bound states below two-meson thresholds.

Contribution

First lattice QCD investigation of $qq' ar b ar b$ tetraquarks showing they are strongly bound and stable, with detailed analysis of different channels and operators.

Findings

Identified stable $J^P=1^+$ tetraquarks below thresholds

Found binding energies of 189(10) and 98(7) MeV

Used multiple pion masses to confirm results

Abstract

We investigate the possibility of $qq^\prime \bar b \bar b$ tetraquark bound states using $n_f=2+1$ lattice QCD ensembles with pion masses $\simeq 164$, $299$, and $415$ MeV. Motivated by observations from heavy baryon phenomenology, we consider two lattice interpolating operators both of which are expected to couple efficiently to tetraquark states: one with diquark-antidiquark and one with a meson-meson structure. Using nonrelativistic QCD to simulate the bottom quarks, we study the $ud\bar b \bar b$, $\ell s\bar b \bar b$ channels with $\ell=u,d$, and find unambiguous signals for strong-interaction-stable $J^P=1^+$ tetraquarks. These states are found to lie $189(10)$ and $98(7)$ MeV below the corresponding free two-meson thresholds.