1+ XTZ States within QCD Sum Rules

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).