1. N* Production from J/ decays at BES
Ji Xiaobin
IHEP, Beijing
(Representing BES Collaboration)
Sep , 2004
QCD and Light Hadrons (Beijing, China)

2. Outline Introduction Baryon program at BES N* in the decay of
N* and * in the decay of and others
Summary
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3. The Beijing Electron Positron Collider
L ~ ~51030 /cm2s at J/ peak
Ecm~2-5 GeV
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4. BESII Detector VC: xy = 100 m TOF: T = 180 ps  counter: r= 3 cm
MDC: xy = m BSC: E/E= 22 % z = 5.5 cm
dE/dx= 8.5 %  = 7.9 mr B field: T
p/p=1.78%(1+p2) z = 3.1 cm
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5. Study of Excited Baryon States
Motivation
Probe the internal structure of light quark baryons
Search for missing baryons predicted by quark model
Obtain a better understanding of the strong interaction force in the non-perturbative regime
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6. relatively large branching ratios (PDG2004)
J/ decays
relatively large branching ratios (PDG2004)
processes
branching ratios(10-3)
N* decays
1.10.1
6.00.5
2.00.1
2.10.2
0.90.4
1.30.3
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7. Pure isospin 1/2 For and , N
Feynman diagram of the production of
For and , N
and N systems are limited to be pure isospin 1/2.
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8. from BES II data Events selection 2 good charged tracks Q1+Q2 = 0
|cos| < 0.8
PID: TOF and dE/dx
Mp > 1.15 GeV
0.88<Mmiss<1.0 GeV
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9. Background Analysis
Estimate the background from the fitting of the data
The Monte Carlo of J/ inclusive decay is also used in the background analysis
Background < 8%
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10. N* in ? L=0 limits it to be BES II Preliminary 3/2+ or 1/2+ N*(1520)
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11. N* in Dalitz Plot: BES II Preliminary Acceptance and other
reasons make the plot
asymmetry.
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12. N* in
Fitting formular k : momentum of anti-neutron q : proton momentum in Mx frame
BES II Preliminary
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13. N* in Preliminary results: Possible new N* resonance
L=0 limits it to be 3/2+ or 1/2+
Detailed information need PWA
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14. N* in
BES II Preliminary
BES II Preliminary
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15. from BES II data Events selection 4 good charged tracks
PID: kaon and at least 1 proton ID
2 (4C)<20
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16. from BES II data BES II Preliminary
*(1520)
*(1690)
PS, eff. corrected
(Arbitrary normalization)
BES II Preliminary
Two clear peaks at 1520, 1690 MeV/c2 in pK mass
N* in K mass
PWA is being performed
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17. from BES II data BES II Preliminary PWA is being performed
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18. Summary BES II preliminary results: A possible “missing” N* is found
PWA to BESII 58M data is in progress
Clear two peaks around 1520, 1690 in pK mass
N* in K mass
PWA is being performed
Similar structure with
PWA is in progress
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19. Thank You!
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20. “Missing” N* Problem Capstick et al.
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