Observation of a charged charmoniumlike structure in e+ e- → π+ π- J/ψ at sqrt[s] = 4.26  GeV

• Published in: Physical review letters 2013-06, Vol.110 (25), p.252001-252001
• Main Authors: Ablikim, M, Achasov, M N, Ai, X C, Albayrak, O, Ambrose, D J, An, F F, An, Q, Bai, J Z, Baldini Ferroli, R, Ban, Y, Becker, J, Bennett, J V, Bertani, M, Bian, J M, Boger, E, Bondarenko, O, Boyko, I, Briere, R A, Bytev, V, Cai, H, Cai, X, Cakir, O, Calcaterra, A, Cao, G F, Cetin, S A, Chang, J F, Chelkov, G, Chen, G, Chen, H S, Chen, J C, Chen, M L, Chen, S J, Chen, X, Chen, Y B, Cheng, H P, Chu, Y P, Cronin-Hennessy, D, Dai, H L, Dai, J P, Dedovich, D, Deng, Z Y, Denig, A, Denysenko, I, Destefanis, M, Ding, W M, Ding, Y, Dong, L Y, Dong, M Y, Du, S X, Fang, J, Fang, S S, Fava, L, Feng, C Q, Friedel, P, Fu, C D, Fu, J L, Fuks, O, Gao, Q, Gao, Y, Geng, C, Goetzen, K, Gong, W X, Gradl, W, Greco, M, Gu, M H, Gu, Y T, Guan, Y H, Guo, A Q, Guo, L B, Guo, T, Guo, Y P, Han, Y L, Harris, F A, He, K L, He, M, He, Z Y, Held, T, Heng, Y K, Hou, Z L, Hu, C, Hu, H M, Hu, J F, Hu, T, Huang, G M, Huang, G S, Huang, J S, Huang, L, Huang, X T, Huang, Y, Huang, Y P, Hussain, T, Ji, C S, Ji, Q, Ji, Q P, Ji, X B, Ji, X L, Jiang, L L, Jiang, X S, Jiao, J B, Jiao, Z
• Format: Article
• Language: English
• ISSN: 1079-7114

We study the process ee+ e- → π+ π- J/ψ at a center-of-mass energy of 4.260 GeV using a 525  pb(-1) data sample collected with the BESIII detector operating at the Beijing Electron Positron Collider. The Born cross section is measured to be (62.9±1.9±3.7)  pb, consistent with the production of the Y(4260). We observe a structure at around 3.9  GeV/c2 in the π(±)J/ψ mass spectrum, which we refer to as the Z(c)(3900). If interpreted as a new particle, it is unusual in that it carries an electric charge and couples to charmonium. A fit to the π(±)J/ψ invariant mass spectrum, neglecting interference, results in a mass of (3899.0±3.6±4.9)  MeV/c2 and a width of (46±10±20)  MeV. Its production ratio is measured to be R = (σ(e+ e- → π(±)Z(c)(3900)(∓) → π+ π- J/ψ)/σ(e+ e- → π+ π- J/ψ)) = (21.5±3.3±7.5)%. In all measurements the first errors are statistical and the second are systematic.