Abstract
The BESIII Collaboration has observed a candidate for a $c \bar c s \bar u$ tetraquark $Z_{cs}$ at $(3982.5^{+1.8}_{-2.6} \pm 2.1)$ MeV and width $(12.8^{+5.3}_{-4.4} \pm 3.0)$ MeV, while the LHCb Collaboration has observed a $Z_{cs}$ candidate in the $\jpsi K^-$ channel with mass of $(4003 \pm 6 ^{+4}_{-14})$ MeV and width $(131 \pm 15 \pm 26)$ MeV. In this note we examine the possibility that these two states are distinct eigenstates of a mixing process similar to that which gives rise to two axial-vector mesons labeled by the Particle Data Group $K_1(1270)$ and $K_1(1400)$. The main point is that on top of a $\bar c c$ pair, the $Z_{cs}$ states have the same light quark content as the $K_1$-s. In the compact tetraquark picture this implies several additional states, analogous to members of the $K_1$ nonet. These states have not yet been observed, nor are they required in the molecular approach. Thus experimental discovery or exclusion of these extra states will be a critical test for competing models of exotic mesons with hidden charm.
Highlights
The discovery of mesons with minimal quark configuration ccqq 0, where q and q0 are light quarks u, d, s, was pioneered by the observation [1] of the Xð3872Þ
Within the compact tetraquark model, this implies the existence of a flavor SUð3Þ nonet whose neutral members have JPC 1⁄4 1þþ, as well as candidates for membership in a 1þ− nonet [3,4,5,6,7]
The mass eigenstates arise from mixing between K1A 1⁄4 3P1 and K1B 1⁄4 1P1, for instance as a result of sharing KÃð892Þπ and Kρ decay modes [19,20]
Summary
The discovery of mesons with minimal quark configuration ccqq 0, where q and q0 are light quarks u, d, s, was pioneered by the observation [1] of the Xð3872Þ. Within the compact tetraquark model, this implies the existence of a flavor SUð3Þ nonet whose neutral members have JPC 1⁄4 1þþ, as well as candidates for membership in a 1þ− nonet [3,4,5,6,7].1. The BESIII Collaboration has observed a candidate for a ccsutetraquark Zcs at ð3982.5þ−21..68. Æ 3.0Þ MeV [8], while the LHCb Collaboration has observed a Zcs candidate in the. We propose that within the compact tetraquark model these two states are likely to be distinct eigenstates of a mixing process similar to that which gives rise to two axialvector strange mesons labeled by the Particle Data Group [14] K1ð1270Þ and K1ð1400Þ.
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