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

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 5-parameter Hamiltonian that includes spin-orbit and tensor terms. After discussing the experimental status of the observed JPC=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.