Observation of Two New N* Peaks in J/psi -> $pp{i}^{-}\bar{n}$ and $\bar{p}{\pi }^{+}n$ Decays

Abstract

The $\pi N$ system in decays of $J/\psi \to \bar{N}N\pi$ is limited to be isospin 1/2 by isospin conservation. This provides a big advantage in studying $N^{\ast }\to \pi N$ compared with $\pi N$ and $\gamma N$ experiments which mix isospin 1/2 and 3/2 for the $\pi N$ system. Using 58 million $J/\psi$ decays collected with the Beijing Electron Positron Collider, more than 100 thousand $J/\psi \to p{\pi }^{-}\bar{n}+c.c.$ events are obtained. Besides two well known $N^{\ast }$ peaks at 1500 MeV and 1670 MeV, there are two new, clear $N^{\ast }$ peaks in the $p\pi$ invariant mass spectrum around 1360 MeV and 2030 MeV. They are the first direct observation of the $N^{\ast }(1440)$ peak and a long-sought "missing" $N^{\ast }$ peak above 2 GeV in the $\pi N$ invariant mass spectrum. A simple Breit-Wigner fit gives the mass and width for the $N^{\ast }(1440)$ peak as $1358\pm 6\pm 16$ MeV and $179\pm 26\pm 50$ MeV, and for the new $N^{\ast }$ peak above 2 GeV as $2068\pm 3_{-40}^{+15}$ MeV and $165\pm 14\pm 40$ MeV, respectively.

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Cited by in corpus (41)

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• First measurements of J/Psi decays into ${\Sigma }^{+}{\bar{\Sigma }}^{-}$ and ${\Xi }^0{\bar{\Xi }}^0$
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• Photoproduction of $\eta$ mesons off the proton for $1.2<E_{\gamma }<4.7$ GeV using CLAS at Jefferson Laboratory
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• On $pp\to pK\Lambda ,NK\Sigma ,pp\varphi$ -- the basic ingredients for strangeness production in heavy ion collisions
• Disentangle the nature of resonances in coupled-channel models
• Partial wave analyses of $\psi (3686)\to p\bar{p}{\pi }^0$ and $\psi (3686)\to p\bar{p}\eta$
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