Spectroscopy of hidden-charm tetraquarks in diquark model
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Spectroscopy of hidden-charm tetraquarks in diquark model Zahra Ghalenovia
, Masoumeh Moazzen Sorkhi
Department of Physics, Kosar University of Bojnord, Bojnord, Iran Received: 8 November 2019 / Accepted: 17 March 2020 © Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract A nonrelativistic model is used to study hidden-charm tetraquarks within a diquark–antidiquark configuration. Using the perturbation theory, we estimate the masses of the heavy tetraquarks with hidden charm. Our present analysis suggests the charmonium-like states: X (3860), X (3872), Z c (3943), X (4140), Z c (4430) and X (4700) can be accommodated in tetraquark picture. We particularly find that the Z c (4430) may be treated as the first radial excitation of X (3872).
1 Introduction The history of the X Y Z exotic states can be traced back to discovery of the X (3872) as the first charmonium-like candidate for a exotic meson. First it has been found by the Belle Collaboration in 2003 [1] and then confirmed by the various experiments [2–5]. Since then, significant experimental development has been achieved in charmonium and bottonium spectroscopy and more unexpected X Y Z states were observed [6–18] and the theoretical understanding of hadron structures is conflicted among the community [19–38]. The structure of exotic mesons has not been understood well, and many theoretical explanations are proposed to study these newly observed systems such as lattice QCD [39–43], the molecular states [44– 54], dynamically generated resonances [55,56], QCD sum rules [57–64], coupled-channel effects [65,66], compact tetraquark states (diquark–antidiquark states) [67–78] and nonrelativistic effective field theories [79]. However, the exotic states consisting of two quarks and two antiquarks are not ruled out in quantum chromodynamics, but cannot be accommodated within the naive quark model and are therefore of special interest. In the diquark–antidiquark picture, the constituent objects of tetraquark systems are a diquark and an antidiquark. Namely, although a diquark cannot be a color singlet, the attraction between two quarks can be strong, as various approaches have shown [80–84]. The diquark is an important object for the understanding of baryon structure and is also important for the understanding of tetraquarks as unconventional mesons. In the present study, we interpret the exotic states as tetraquark systems. Among the tetraquark states, those consisting of diquark and antiquark are of interest to study. We solve the tetraquark problem in a two-step procedure: First, we use a quark–quark interaction Hamiltonian in order to obtain the mass of a constituent “good diquark” of the type [q, q ]. Second, we regard the diquarks
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as point-like objects and use a diquark–antidiquark interaction Hamiltonian in order to obtain the tetraquark masses. This work is organized as f
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