Electromagnetic form factors and structure of the $T_{bb}$ tetraquark

TL;DR

This study uses lattice QCD to calculate the electromagnetic form factors of the $T_{bb}$ tetraquark, revealing its internal structure as a compact diquark-antidiquark system with specific spin and color configurations.

Contribution

First lattice QCD calculation of electromagnetic form factors for a $T_{bb}$ tetraquark, providing insights into its internal structure and charge distributions.

Findings

Evidence of a compact heavy diquark $[bb]$ in spin one

Light antidiquark $[ar u ar d]$ in spin zero

Charge and magnetic distributions characterized

Abstract

We present the first lattice QCD calculation of electromagnetic form factors of a tetraquark, focusing on the $T_{bb} = bb\bar u \bar d$ with quantum numbers $I(J^P) = 0(1^+)$. The electromagnetic current probes the charge monopole, magnetic dipole and the electric quadrupole distributions within the tetraquark. From it, we find evidence that its structure consists of a compact heavy diquark $[bb]$ in spin one, color-antitriplet configuration, and a light antidiquark $[\bar u \bar d]$ in spin zero, color-triplet configuration. The computations were performed on a single CLS ensemble with $N_f = 2+1$ dynamical quarks at a lattice spacing $a\approx 0.064$ fm and with a pion mass $m_\pi \approx 290$ MeV.