Shedding light on the nature of $\ddot{I}•(2170)$ with the parton and hadron cascade model PACIAE

Abstract

The nature of $\ddot{I}•(2170)$ remains open. We simulate its production in $e^{+}{e}^{-}$ collisions at $\sqrt{s}=4.95$ GeV using PACIAE 4.0, which sequentially generates the final partonic state (FPS) and the final hadronic state (FHS). While previous studies have interpreted $\ddot{I}•(2170)$ as an $ss\bar{s}\bar{s}$ or a $u\bar{u}s\bar{s}$ state, the $U(1)$ anomaly coupling allows non-strange quarks to couple to a vector $s\bar{s}$ component via soft-gluon interactions. This motivates us to also explore the $d\bar{d}s\bar{s}$ tetraquark configuration. In addition, we consider $\ddot{I}•(2170)$ as an excited strangeonium state, an $s\bar{s}g$ hybrid state, a $\bar{\hat{I}}›\hat{I}›$ bound state, and a $\ddot{I}•K^{+}{K}^{-}$ resonance state. The strangeonium, hybrid, and tetraquark candidates are formed by coalescing their constituent partons in the FPS using the dynamically constrained phase-space coalescence model. The $\bar{\hat{I}}›\hat{I}›$ and $\ddot{I}•K^{+}{K}^{-}$ states are produced via recombination of their constituent hadrons in the FHS. We calculate the orbital angular momentum quantum number of each candidate in its rest frame and perform spectral classification. Given $J^{PC}=1^{--}$, $\ddot{I}•(2170)$ can be interpreted as a $D$-wave $s\bar{s}$, a $P$-wave $s\bar{s}g$, a $P$-wave $u\bar{u}s\bar{s}/d\bar{d}s\bar{s}/ss\bar{s}\bar{s}$, an $S$-wave $\bar{\hat{I}}›\hat{I}›$, or an $S$-wave $\ddot{I}•K^{+}{K}^{-}$ state. The yields of the $D$-wave $s\bar{s}$, $P$-wave $s\bar{s}g$, $u\bar{u}s\bar{s}$ and $d\bar{d}s\bar{s}$ states are of order $10^{-4}$; those for the $S$-wave $\bar{\hat{I}}›\hat{I}›$ and $\ddot{I}•K^{+}{K}^{-}$ states are of order $10^{-5}$; while the $P$-wave $ss\bar{s}\bar{s}$ yield is of order $10^{-6}$. Moreover, significant discrepancies are observed in the rapidity distributions and the $p_T$ spectra among the various candidates. These discrepancies could serve as valuable criteria for unraveling the nature of $\ddot{I}•(2170)$.

8 pages, 3 tables, 2 figures. Some modifications are made in section II