Determination of the Mass and the Energy Spectra of Heavy Pentaquarks in the Diquark Model
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Seyd Mohammad Moosavi Nejad · Aida Armat
Determination of the Mass and the Energy Spectra of Heavy Pentaquarks in the Diquark Model
Received: 31 May 2020 / Accepted: 7 August 2020 © Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract In recent years, study of pentaquarks as the exotic states of multiquark particles have been in progress experimentally and theoretically. A motivation for studying these new particles has been to better understanding of the strong interactions and the QCD theory. In this work, our aim is to calculate the mass spectrum of possible heavy pentaquarks for which we consider a two-body system containing an antiquark and two-diquarks. Using the Cornell potential and the spin–spin interaction we, first, calculate the diquarks masses and in the following the masses and the spin-dependent energies of heavy pentaquarks in their ground states. We will compare our theoretical result for Pc = c¯ [cu]s=1 [ud]s=0 , Jp = 3/2− with the value reported by the LHCb collaboration.
1 Introduction In the conventional quark model of Standard Model (SM) theory, the well-known composite particles are formed of quark–antiquark pairs (mesons) or three quarks/antiquarks (baryons). Therefore, any particle which is not classified within this model is known as an exotic hadron. The only necessary condition for new states is to be color singlets. When Murray Gell-Mann and George Zweig proposed the quark model in their 1964 papers, they mentioned the possibility of exotic hadrons such as pentaquarks (states with a valence structure of four quarks and one antiquark) [1]. From this point of view, the concept of multiquark particles has a long history, however it took long time to find the first clear evidence. Meanwhile, their discovery will allow physicists to study the strong force in greater details and have a better understanding of the theory of Quantum Chromodynamics (QCD) which describes the theory of strong interactions. Historically, within the past decade, scientists have studied on new exotic particles such as X (3872) [2] and Zc . The decay of Zc into J/ψ (a bound state of charm-anticharm quarks) suggested that this particle is formed of two quarks and two antiquarks. The existence of this four-quark state (or tetraquark) leads to the prediction of states with five-quark which are known as pentaquarks, see Refs. [3,4]. Nowadays, multiquark resonances are observed experimentally, so that the number of these exotic states and our knowledge of their properties have been growing over the years [5]. In this regard, the physics of pentaquarks has been renovated very recently, as the LHCb Collaboration reported three heavy pentaquarks, Pc ’s. In Ref. [6], the LHCb collaboration has reported the discovery of a narrow pentaquark state, Pc (4312)+ , decaying to J/ψp with a statistical significance of 7.3σ in a data sample of 0b → J/ψ + p + K− decays which is one order of magnitude larger than that previous analysis by the LHCb collaboration [7]. In Ref. [6], the pentaquark structure of Pc (4450
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