Observation of an anomalous line shape of the $\eta^{\prime}\pi^{+}\pi^{-}$ mass spectrum near the $p\bar{p}$ mass threshold in $J/\psi\rightarrow\gamma\eta^{\prime}\pi^{+}\pi^{-}$

Using $1.09 \times 10^{9}$ $J / ψ$ events collected by the BESIII experiment in 2012, we study the $J / ψ \to γ η^{'} π^{+} π^{-}$ process and observe a significant abrupt change in the slope of the $η^{'} π^{+} π^{-}$ invariant mass distribution at the proton-antiproton ( $p \overset{ˉ}{p}$ ) mass threshold. We use two models to characterize the $η^{'} π^{+} π^{-}$ line shape around $1.85 GeV / c^{2}$ : 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 $1.85 GeV / c^{2}$ with strong couplings to $p \overset{ˉ}{p}$ final states or a narrow state just below the $p \overset{ˉ}{p}$ mass threshold. Although we cannot distinguish between the fits, either one supports the existence of a $p \overset{ˉ}{p}$ molecule-like state or bound state with greater than $7 σ$ significance.

Observation of an anomalous line shape of the $η^{'} π^{+} π^{-}$ mass spectrum near the $p \overset{ˉ}{p}$ mass threshold in $J / ψ \to γ η^{'} π^{+} π^{-}$

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Observation of an anomalous line shape of the $η^{'} π^{+} π^{-}$ mass spectrum near the $p \overset{ˉ}{p}$ mass threshold in $J / ψ \to γ η^{'} π^{+} π^{-}$

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Observation of an anomalous line shape of the η′π+π−η′π+π− mass spectrum near the ppˉppˉ​ mass threshold in J/ψ→γη′π+π−J/ψ→γη′π+π−

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Observation of an anomalous line shape of the η′π+π−η′π+π− mass spectrum near the ppˉppˉ​ mass threshold in J/ψ→γη′π+π−J/ψ→γη′π+π−

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Observation of an anomalous line shape of the $η^{'} π^{+} π^{-}$ mass spectrum near the $p \overset{ˉ}{p}$ mass threshold in $J / ψ \to γ η^{'} π^{+} π^{-}$

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Observation of an anomalous line shape of the $η^{'} π^{+} π^{-}$ mass spectrum near the $p \overset{ˉ}{p}$ mass threshold in $J / ψ \to γ η^{'} π^{+} π^{-}$

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AI智能校验