Zc and Zcs systems with operator mixing at NLO in QCD sum rules

Abstract

Abstract We study the mass spectra of hidden-charm tetraquark systems with quantum numbers (IG)JP = (1+)1+ (and their I = $$ \frac{1}{2} $$ 1 2 partners) using QCD sum rules. The analysis incorporates the complete next-to-leading order (NLO) contribution to the perturbative QCD part of the operator product expansions, with particular attention to operator mixing effects due to renormalization group evolution. We find that both the parametric dependence and the perturbative convergence are significantly improved for the two mixed operators $$ {J}_{1,5}^{\textrm{Mixed}} $$ J 1 , 5 Mixed and $$ {J}_{2,6}^{\textrm{Mixed}} $$ J 2 , 6 Mixed , compared with those for the unmixed meson-meson or diquark-antidiquark type ones. For the $$ \overline{d}c\overline{c}u $$ d ¯ c c ¯ u system, the masses of $$ {J}_{1,5}^{\textrm{Mixed}} $$ J 1 , 5 Mixed and $$ {J}_{2,6}^{\textrm{Mixed}} $$ J 2 , 6 Mixed are determined to be $$ {3.89}_{-0.12}^{+0.18} $$ 3.89 − 0.12 + 0.18 GeV and $$ {4.03}_{-0.07}^{+0.06} $$ 4.03 − 0.07 + 0.06 GeV, respectively, closely matching those of Zc(3900) and Zc(4020). Similarly, for the $$ \overline{s}c\overline{c}u $$ s ¯ c c ¯ u states, the masses of $$ {J}_{1,5}^{\textrm{Mixed}} $$ J 1 , 5 Mixed and $$ {J}_{2,6}^{\textrm{Mixed}} $$ J 2 , 6 Mixed are found to be $$ {4.02}_{-0.09}^{+0.17} $$ 4.02 − 0.09 + 0.17 GeV and $$ {4.21}_{-0.07}^{+0.08} $$ 4.21 − 0.07 + 0.08 GeV, respectively, in close proximity to Zcs(3985)/Zcs(4000) and Zcs(4220), consistent with the expectation that they are the partners of Zc(3900) and Zc(4020). Our results highlight the crucial role of operator mixing, an inevitable effect in a complete NLO calculation, in achieving a robust phenomenological description for the tetraquark system.