Spectrum of p -wave hidden-charm exotic mesons in the diquark model

Abstract

We study the fine structure in the spectrum of known and predicted negative-parity hidden-charm exotic meson states, which comprise the lowest P -wave multiplet in the dynamical diquark model. Starting with a form previously shown to successfully describe the S-wave states, we develop a 5parameter Hamiltonian that includes spin-orbit and tensor terms. After discussing the experimental status of the observed J P C = 1 −− states Y with respect to masses and decay modes (classified by eigenvalues of heavy-quark spin), we note a number of inconsistencies between measurements from different experiments that complicate a unique determination of the spectrum. Outlining a variety of scenarios for interpreting the Y data, we perform fits to each one, obtaining results that demonstrate differing possibilities for the P -wave spectra. Choosing one of these fits for illustration, we predict masses for all 28 isomultiplets in this 1P multiplet, compare the results to tantalizing hints in the data, and discuss the rich discovery potential for new states.

Study of the process e+e−→π0π0J/ψ and neutral charmoniumlike state Ablikim1, Ачасов2, Adlarson3 et al. 2020Phys. Rev. D

“…Despite several experimental observations, the internal constituents of the Yð4220Þ are still unclear. Possible interpretations include hybrids, meson molecules, hadrocharmonium, or tetraquarks, etc., but none of them are conclusive [9][10][11][12][13].…”

“…A partial-wave analysis (PWA) [14] showed that the charged charmoniumlike state Z c ð3900Þ AE , observed in decays to π AE J=ψ in the process e þ e − → π þ π − J=ψ [3,15], and to D ÃD in the process e þ e − → π AE ðD ÃD Þ ∓ [16], has spin-parity J P ¼ 1 þ . Different theoretical models [9][10][11][12][13] consider the Z c ð3900Þ AE to be an unconventional state; in particular, the molecular and tetraquark interpretation [11,13], suggested a strong correlation of the Yð4220Þ to πZ c ð3900Þ. However, further studies are needed to clarify the situation.…”

Simple spectrum of cc¯cc¯ states in the dynamical diquark model

“…In the study of P-wave ccqq 0 states in Ref. [40], the tensor operator is assumed to originate as an analogue to the corresponding operator in nucleon-nucleon interactions arising from pion exchange, and therefore σ couples only to the light quarks within δ andδ, just as for the spin-spin V 0 operator in Eq. (3).…”

“…We nevertheless also present an initial fit to the cccc spectrum, using numerical values for the Hamiltonian parameters obtained from the analogous operators in other sectors of exotics to which the model has previously been applied. Specifically, the strength of the spin-spin operator is obtained from a recent fit to ccss candidates [41], and the spin-orbit and tensor strengths are taken from a recent fit to P-wave ccqq 0 candidates [40].…”

“…In contrast, the tensor operator for P-wave ccqq 0 states in Ref. [40], owing its origin to a pionlike exchange within the state, was chosen to couple only to the light-quark spins within the diquarks. Nevertheless, the matrix elements for an alternative tensor operator that couples only to the full diquark spins (as to be used here) are also computed in that work.…”