Hidden and Open Heavy-Flavor Hadronic States
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H. Garcilazo · A. Valcarce
Hidden and Open Heavy-Flavor Hadronic States
Received: 11 March 2020 / Accepted: 1 July 2020 © Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract We discuss the stability of hidden and open heavy-flavor hadronic states made of either two or three mesons. References are made in passing to studies regarding two and three-body systems containing baryons. We perform a comparative study analyzing the results in terms of quark and hadron degrees of freedom. Compact and molecular states are found to exist in very specific situations. We estimate the decay width for the different scenarios: weak decays for bound states by the strong interaction, and strong decays for hadronic resonances above a decay threshold. The experimental observation of narrow hadrons lying well above their lowest decay threshold is theoretically justified.
1 Introduction The hadron spectra above open-flavor thresholds has emerged as a key issue to understand QCD in the lowenergy regime. The experimental hadron spectra below open-flavor thresholds follow closely a naive quarkantiquark (q q) ¯ or three-quark (qqq) structure according to SU (3) irreducible representations [1]. However, since 2003, several resonances reported by different experimental collaborations appeared close to a twohadron threshold, presenting properties that makes a naive quark substructure unlikely. See, for example, Refs. [2–8] and references therein. Although this observation could be coincidental due to the large number of open-flavor thresholds in the energy region where the new intriguing states have been reported, it could also point to a close relation between some particular thresholds and resonances contributing to the standard hadron spectroscopy. The possible existence of hadrons with a quark content richer than q q¯ or qqq states is nowadays a hot topic in hadron spectroscopy. Experimental discoveries have stimulated a flurry of theoretical studies dealing with multiquark states and hadron-hadron resonances with a variety of different methodological approaches. It is important to note at the outset that conclusions drawn from hadron-hadron resonance analyses or a multiquark constituent picture should be similar, provided that, in general, a coupled-channel hadron-hadron approach would be mandatory in order to reproduce the multiquark constituent picture. To be more specific, let us note that multiquark systems present a richer color structure than standard baryons or mesons. Whereas the color wave function for standard mesons and baryons is made of a single vector, for multiquark states there are different vectors leading to a color singlet. For example, for four-quark states one can get a color singlet ¯ or 66) ¯ components. Any colored component, better out of colorless singlet-singlet (11) or colored (88, 33, H. Garcilazo Escuela Superior de Física y Matemáticas, Instituto Politécnico Nacional, Edificio 9, 07738 Mexico, DF, Mexico E-mail: [email protected] A. Valcarce (B) Departamento de Física Fundamental, Unive
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