@techreport{68f98b5158014e19b9751d491ba16c15,

title = "Observation of an anomalous line shape of the $η^{\prime}π^{+}π^{-}$ mass spectrum near the $p\bar{p}$ mass threshold in $J/ψ\rightarrowγη^{\prime}π^{+}π^{-}$",

abstract = "Using $1.09\times10^{9}$ $J/\psi$ events collected by the BESIII experiment in 2012, we study the $J/\psi\rightarrow\gamma\eta^{\prime}\pi^{+}\pi^{-}$ process and observe a significant abrupt change in the slope of the $\eta^{\prime}\pi^{+}\pi^{-}$ invariant mass distribution at the proton-antiproton ($p\bar{p}$) mass threshold. We use two models to characterize the $\eta^{\prime}\pi^{+}\pi^{-}$ line shape around $1.85~\text{GeV}/c^{2}$: one which explicitly incorporates the opening of a decay threshold in the mass spectrum (Flatt\'{e} formula), and another which is the coherent sum of two resonant amplitudes. Both fits show almost equally good agreement with data, and suggest the existence of either a broad state around $1.85~\text{GeV}/c^{2}$ with strong couplings to $p\bar{p}$ final states or a narrow state just below the $p\bar{p}$ mass threshold. Although we cannot distinguish between the fits, either one supports the existence of a $p\bar{p}$ molecule-like state or bound state with greater than $7\sigma$ significance.",

keywords = "hep-ex",

author = "M. Ablikim and Achasov, {M. N.} and S. Ahmed and Ai, {X. C.} and O. Albayrak and M. Albrecht and Ambrose, {D. J.} and A. Amoroso and An, {F. F.} and Q. An and Bai, {J. Z.} and Ferroli, {R. Baldini} and Y. Ban and Bennett, {D. W.} and Bennett, {J. V.} and N. Berger and M. Bertani and D. Bettoni and Bian, {J. M.} and F. Bianchi and E. Boger and I. Boyko and Briere, {R. A.} and H. Cai and X. Cai and O. Cakir and A. Calcaterra and Cao, {G. F.} and Cetin, {S. A.} and Chang, {J. F.} and G. Chelkov and G. Chen and Chen, {H. S.} and Chen, {H. Y.} and Chen, {J. C.} and Chen, {M. L.} and S. Chen and Chen, {S. J.} and X. Chen and Chen, {X. R.} and Chen, {Y. B.} and Cheng, {H. P.} and Chu, {X. K.} and G. Cibinetto and Z. Haddadi and N. Kalantar-Nayestanaki and M. Kavatsyuk and H. Loehner and J.G. Messchendorp and M. Tiemens and {BESIII Collaboration}",

year = "2016",

month = mar,

day = "31",

language = "English",

type = "WorkingPaper",

}