New charged resonance $Z_{c}^{-}(4100)$: the spectroscopic parameters and width

Abstract

The mass, coupling and width of the newly observed charged resonance Z − c (4100) are calculated by treating it as a scalar four-quark system with a diquark-antidiquark structure. The mass and coupling of the state Z − c (4100) are calculated using the QCD two-point sum rules. In these calculations we take into account contributions of the quark, gluon and mixed condensates up to dimension ten. The spectroscopic parameters of Z − c (4100) obtained by this way are employed to study its Swave decays to ηc(1S)π − , ηc(2S)π − , D 0 D − , and J/ψρ − final states. To this end, we evaluate the strong coupling constants corresponding to the vertices Zcηc(1S)π − , Zcηc(2S)π − , ZcD 0 D − , and ZcJ/ψρ − respectively. The couplings gZ cηc1 π , gZ cηc2π , and gZ cDD are computed by means of the QCD three-point sum rule method, whereas g ZcJ/ψρ is obtained from the QCD light-cone sum rule approach and soft-meson approximation. Our results for the mass m = (4080 ± 150) MeV and total width Γ = (147 ± 19) MeV of the resonance Z − c (4100) are in excellent agreement with the existing LHCb data. I. INTRODUCTIONRecently, the LHCb Collaboration reported on evidence for andecays extracted from analysis of pp collisions' data collected with LHCb detector at center-of-mass energies of √ s = 7, 8 and 13 TeV [1]. The mass and width of this new Z − c (4100) resonance (hereafter Z c ) were found equal to m = 4096 ± 20 +18 −22 MeV and Γ = 152 ± 58 +60 −35 MeV, respectively. As it was emphasized in Ref.[1], the spinparity assignments J P = 0 + and J P = 1 − both are consistent with the data.From analysis of the decay channel Z c → η c (1S)π − it becomes evident that Z c contains four quarks cdcu, and it is presumably another member of the family of charged exotic Z-resonances with the same quark content; the well-known axial-vector tetraquarks Z ± c (4430) and Z ± c (3900) are also built of the quarks cdcu or cucd. The Z ± c (4430) were discovered and studied by the Belle Collaboration in B meson decays B → Kψ ′ π ± as resonances in the ψ ′ π ± invariant mass distributions [2][3][4]. The decay of Z + c (4430) to the final state J/ψπ + also was detected in the Belle experiment [5]. The existence of the Z ± c (4430) resonances was confirmed by the LHCb Collaboration as well [6,7].Another well-known members of this family are the axial-vector states Z ± c (3900), which were detected by the BESIII Collaboration in the process e + e − → J/ψπ + π − as peaks in the J/ψπ ± invariant mass distributions [8]. These structures were seen by the Belle and CLEO collaborations as well (see Refs. [9,10]). The BESIII informed also on observation of the neutral Z 0 c (3900) state in the process e + e − → π 0 Z 0 c → π 0 π 0 J/ψ [11]. Various theoretical models and approaches were employed to reveal the internal quark-gluon structure and determine parameters of the charged Z-resonances. Thus, they were considered as hadrocharmonium com-pounds or tightly bound diquark-antidiquark states, were treated as the four-quark systems built of conventional mesons or inte...