1+ XTZ States within QCD Sum Rules

TL;DR

This paper uses QCD sum rules to estimate properties of exotic hadrons, confirming the tetraquark and molecule nature of certain states and providing precise mass predictions across charm and beauty sectors.

Contribution

It introduces improved QCD sum rule methods to analyze exotic states, offering new mass estimates and insights into their tetraquark and molecular structures.

Findings

Confirmed $X_c(3872)$ and $Z_c(3900)$ as tetramoles states.

Predicted masses for $T_{cc}^{1^+}$, $Z_b$, and $X_b$ states.

Compared results with lattice and quark model approaches.

Abstract

We present improved estimates of the couplings, masses and mass ratios of the $X_Q, Z_Q$ and $T_{QQ\bar q\bar q'}$ states using (inverse) QCD Laplace sum rules (LSR), their ratios ${\cal R}$ and double ratios (DRSR), within stability criteria. We conclude that the observed $X_c(3872)$ and $Z_c(3900)$ are tetramoles states (superposition of quasi-degenerated molecule and tetraquark states having similar couplings to the currents) with the predicted masses: $M_{{\cal T}_{X_c}}=3876(44)$ MeV and $M_{{\cal T}_{Z_c}}=3900(42)$ MeV. We also do an extensive analysis of the four-quark nature of different $T_{QQ\bar q\bar q'}$ axial-vector states. Then, combining ${\cal R}$ and DRSR, we reanalyze the observed state $X_c(3872)$ and we obtain a precise prediction of $M_{T_{cc}^{1^+}}$=3886(6) MeV. Extending to the beauty sector, we find the results: $M_{{\cal T}_{Z_b}}=10579(99)$ MeV and $M_{X_b}=10545(131)$ MeV. Finally, we confront our combined LSR $\oplus$ DRSR results with the ones from some other approaches (lattices and quark models).