Hunting for the heavy quark spin symmetry partner of $Z_{cs}$

Abstract

The discovery of a charged strange hidden-charm state $Z_{cs}$(3985) implies another higher $Z_{cs}^{\ast }$ state coupling to ${\bar{D}}_s^{\ast -}{D}^{\ast 0}+c.c$ under the heavy quark spin symmetry. In this paper we discuss a possible hunt for it with data taken at existing facilities. We point out a hint for $Z_{cs}^{\ast }$ in the data of ${\bar{B}}_s^0\to J/\psi K^{-}{K}^{+}$ at LHCb, though weak, in line with the production mechanism of pentaquark $P_c$. We also study the triangular singularity which would possibly enhance the production of $Z_{cs}^{\ast }$ in electron-positron collision. Surprisingly, the production rate of $Z_{cs}^{\ast }$ is expected to be maximum at the $e^{+}{e}^{-}$ center of mass energy of 4.648 GeV, which is lower than 4.681 GeV for $Z_{cs}$ due to the inverted coupling hierarchy of $D_{s1}\bar{D}K$ and $D_{s2}{\bar{D}}^{\ast }K$ in the triangle diagrams. Their bottom analogue under heavy quark flavor symmetry is also discussed. Our theoretical analysis would confront with future experiment of LHCb, BESIII, and Bell II.

Comments: 14 pages, 6 figures and 1 table