Observation of two new N* peaks in J / psi ---> p pi- anti-n and anti-p pi+ n decays

Ablikim, M.; Bai, J.Z.; Ban, Y.; Bian, J.G.; Cai, X.; Chang, J.F.; Chen, H.F.; Chen, H.S.; Chen, H.X.; Chen, J.C.

doi:10.1103/PhysRevLett.97.062001

Observation of two new N* peaks in J / psi ---> p pi- anti-n and anti-p pi+ n decays

BES

Collaboration

May, 2004

5 pages

Published in:

Phys.Rev.Lett. 97 (2006) 062001

e-Print:

hep-ex/0405030 [hep-ex]

DOI:

10.1103/PhysRevLett.97.062001

PDG:

{{\mathit N}{(2100)}}

BREIT-WIGNER MASS

Experiments:

BEPC-BES

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Abstract: (arXiv)

The

\pi N

system in decays of

J/\psi\to\bar NN\pi

is limited to be isospin 1/2 by isospin conservation. This provides a big advantage in studying

N^*\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^*

peaks at 1500 MeV and 1670 MeV, there are two new, clear

N^*

peaks in the

p\pi

invariant mass spectrum around 1360 MeV and 2030 MeV. They are the first direct observation of the

N^*(1440)

peak and a long-sought "missing"

N^*

peak above 2 GeV in the

\pi N

invariant mass spectrum. A simple Breit-Wigner fit gives the mass and width for the

N^*(1440)

peak as

1358\pm 6 \pm 16

MeV and

179\pm 26\pm 50

MeV, and for the new

N^*

peak above 2 GeV as

2068\pm 3^{+15}_{-40}

MeV and

165\pm 14\pm 40

MeV, respectively.

13.75.Gx
14.20.Gk
13.25.Gv
electron positron: colliding beams
electron positron: annihilation
J/psi(3100): electroproduction
J/psi(3100): hadronic decay
nucleon resonance: hadronic decay
mass spectrum: (p pi-)
mass spectrum: (anti-p pi+)

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