Observation of a Charged Charmoniumlike Structure Z_c(4020) and Search for the Z_c(3900) in e+e−→π+π−hc

Charged charmoniumlike structures in the $$e^+ e^- \rightarrow \psi (3686) \pi ^+ \pi ^-$$ process based on the ISPE mechanism

“…In fact, this observation deep- Fig. 1 The predicted charged charmoniumlike structures appearing in J/ψπ ± , h c π ± and ψ(2S)π ± invariant mass spectrum and the corresponding experimental discoveries [9,12,15] ens our confidence again. As shown in Fig.…”

“…In 2013, the BESIII and Belle collaborations indeed discovered a charged charmonium-like Z c (3900) in the process e + e − → J/ψπ + π − around √ s = 4.26 GeV [9,10], which was quickly and further confirmed by CLEO-c in the same process but at √ s = 4.17 GeV [11]. Later, another charged charmoniumlike structure named Z c (4020) was observed in the h c π + invariant mass spectrum of the e + e − → π + π − h c process [12]. Additionally, at the center-of-mass energy of 4.26 GeV, the BESIII Collaboration reported two charged charmoniumlike structures, Z c (3885) in the (D * D ) ± invariant mass spectrum of e + e − → π ∓ (D * D ) ± process [13] and Z c (4025) in the (D * D * ) ± invariant mass spectrum of the e + e − → π ∓ (D * D * ) ± process [14].…”

“…After two years of our paper, the BESIII and Belle collaborations discovered a charged charmoniumlike Z c (3900) in the process e + e − → J/ψπ + π − around √ s = 4.26 GeV [9,10], and CLEO-c confirmed it in the same process but at √ s = 4.17 GeV [11]. In 2013, BESIII observed another charged charmoniumlike structure named as Z c (4020) in the h c π + invariant mass spectrum of the e + e − → π + π − h c process [12]. These experimental observations make us believe that the ISPE mechanism indeed plays an important role in producing these novel phenomena.…”

“…In the past years, the BESIII and Belle Collaborations have made a great progress on finding charged charmonium-like XY Z states. A series of charged charmonium-like structures, Z c (3900) [9], Z c (3885) [13], Z c (4020) [12], and Z c (4025) [14], were reported one by one. These experimental results have stimulated a great interest of both theorists and experimentalists since the charged property of these charmonium-like states indicates these states should contain at least four constituent quarks, thus they could be good candidates of tetraquark states.…”

Magnetic moment of Zc(3900) as molecular state

“…The X, Y, Z are representing the axial-vector, vector and charged exotic states, respectively. Up to now, there are eight members in the family of the electrically charged exotic resonances: Z c (3900), Z c (4020), Z c (4200), Z c (4430), Z 1 (4050), Z 2 (4250), Z b (10610), and Z b (10650) discovered in decays into final resonances including a pair of heavy and light quarks [1][2][3][4][5][6][7][8][9][10]. Because of their electric charge they cannot be classified as conventional ̅ resonances, they have to be exotic resonances with minimal quark contents ̅ ̅ .…”