Doubly Heavy Tetraquark Resonant States

TL;DR

This study investigates the spectrum of doubly heavy tetraquarks using a constituent quark model, identifying several narrow resonant states and analyzing their structures and dynamics.

Contribution

It reports new narrow resonant states above decay thresholds and provides a detailed structural interpretation based on quark dynamics, including the mixed nature of certain resonances.

Findings

Discovery of several narrow resonant states above decay thresholds.

Identification of a mixed state of a compact tetraquark and a scattering state.

Resonances exhibit structures consistent with heavy-quark spin symmetry.

Abstract

Spectrum of the doubly heavy tetraquarks, $bb\bar q\bar q$, is studied in a constituent quark model. Four-body problem is solved in a variational method where the real scaling technique is used to identify resonant states above the fall-apart decay thresholds. In addition to the two bound states that were reported in the previous study we have found several narrow resonant states above the $BB^*$ and $B^*B^*$ thresholds. Their structures are studied and are interpreted by the quark dynamics. A narrow resonance with spin-parity $J^P=1^+$ is found to be a mixed state of a compact tetraquark and a $B^*B^*$ scattering state. This is driven by a strong color Coulombic attraction between the $bb$ quarks. Negative-parity excited resonances with $J^P=0^-$, $1^-$ and $2^-$ form a triplet under the heavy-quark spin symmetry. It turns out that they share a similar structure to the $\lambda$-mode of a singly heavy baryon as a result of the strongly attractive correlation for the doubly heavy diquark.