Z + (4430): Nonexotic interpretation
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EMENTARY PARTICLES AND FIELDS Theory
Z + (4430): Nonexotic Interpretation T. V. Uglov1)* and P. N. Pakhlov2)** Received February 20, 2015
Abstract—The possibility of describing the charged charmonium-like state Z + (4430) as the kinematical rescattering effect is examined. This approach makes it possible to avoid the introduction of exotic hadron states in the model, and one describes structures in the ψ(2S)π + mass spectrum by the presence of the (∗) Ds resonance in a hidden intermediate state. The resulting model predictions are compared with the results obtained by the LHCb Collaboration. DOI: 10.1134/S1063778816020198
1. INTRODUCTION According to quantum chromodynamics (QCD), only color-singlet combinations of quarks and (or) antiquarks may form bound states. The simplest of them are mesons (q q¯) and baryons (qqq). The existence of tetraquark (qq q¯q¯), pentaquark (qqqq q¯), or other multiquark combinations was not confirmed experimentally until recently. The recent discovery of an exotic charmonium-like XY Z state revived interest in this topic [1]. Numerous attempts at interpreting the new states in question as excitations of traditional charmomium states led to contradictory results, since this could not explain completely their properties— first of all, the width with respect to decay to opencharm states. The first significant indication of the existence of a bound multiquark state that cannot be interpreted as a traditional charmonium state was obtained by the Belle Collaboration in 2008 from an analysis of the mass spectrum of ψ π + combinations in the decay process B → ψ π + K [2, 3]. The BaBar Collaboration did not observe any significant structures in this process [4], but the LHCb Collaboration confirmed the existence of Z(4430)+ at a significance level of about 14 standard deviations (14σ) in the recent study reported in [5]. Carrying an electrical charge and concurrently containing a c¯ c quark pair, Z(4430)+ has a quark content that is not simpler than c¯ c(q q¯)+ ; therefore, 1)
Moscow Institute of Physics and Technology (State University), Institutskii per. 9, Dolgoprudnyi, Moscow oblast, 141700 Russia. 2) National Research Nuclear University MEPhI, Kashirskoe sh. 31, Moscow, 115409 Russia. * E-mail: [email protected] ** E-mail: [email protected]
it cannot be an excitation of a traditional charmonium state. There are a number of theories that treat Z(4430)+ as a resonance: a tetraquark [6], a molecule [7], a hadrocharmonium [8], a kinemati¯→ cal cusp effect [9], rescattering in the process B D ∗− D1 (2420)K → ψ π + K [10, 11], and initial-state pion emission [12]. In the present study, we propose a new approach [13] that would explain the nature of the structures in the ψ π + spectrum without resort to exotic states. As a development of the ideas initially formu¯ → ψ π+ K − lated in [14], we consider the process B ∗0 + + as the result of D D → ψ π rescattering in the ¯ → Ds(∗)− D+ followed Ds(∗)− → D∗0 K − , decay B (∗)− (∗) is a Ds -meson excitation. While where Ds ∗ the Ds was experimental
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