Two-pion program at WASA

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Wasa-at-Cosy
The ABC Effect in Double-Pionic Nuclear Fusion
and a pn Resonance as its Possible Origin
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ABC effect

• Experimentally
• low-mass enhancement in M??
• observed in many fusion reactions
• accompanied with ?? excitations
• Theoretically
• originates from t-channel ?? excitation
• expected double-hump structure in M?? (not
  supported by experimental observations)

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What we actually did
p
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What we actually did
?
?
?0
d
?0
?
?
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WASA 4? Detector
?
?
d
COSY/
?
?
?
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Total xsection
pp?? d??0
pn?? d??-
pn?? d?0?0
?(??0)?(I1) ?(??-)0.5?(I1)2?(I0) ?(?0?0)?
(I0)0.2?(I1)
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Total x-section
preliminary
?? mass
d?? threshold
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2D x-section
preliminary
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Qualitative description
p
n

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Total xsection slices qualitative description
preliminary
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Total xsection slices qualitative description
preliminary
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Total xsection slices qualitative description
preliminary
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Total xsection slices qualitative description
preliminary
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Total xsection slices qualitative description
preliminary
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Total xsection slices qualitative description
preliminary
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Total xsection slices qualitative description
preliminary
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Total xsection slices qualitative description
preliminary
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Total xsection slices qualitative description
preliminary
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Total xsection slices qualitative description
preliminary
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Total xsection slices qualitative description
preliminary
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Total xsection slices qualitative description
preliminary
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Total xsection slices qualitative description
preliminary
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Total xsection slices qualitative description
preliminary
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Total xsection slices qualitative description
preliminary
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Total xsection slices qualitative description
preliminary
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Total xsection slices qualitative description
preliminary
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Total xsection slices qualitative description
preliminary
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Total xsection slices qualitative description
preliminary
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Total xsection slices qualitative description
preliminary
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Angular distributions
preliminary
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pn ? d?0?0 and pp ? d??0
(p-spectator)
(n-spectator)
preliminary
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??0 invariant mass Tp ? 1GeV
pp ? 2He p0p0
preliminary
pp ? d pp0
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First results on He

• December 07 (dd ? 3He/?X)
• Measurements Td0.8, 0.9, 1.05, 1.117, 1.25,
  1.32, 1.4 GeV

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dd ? 4He p0p0 Invariant Mass p0p0
1.117 GeV
1.05 GeV
0.9 GeV
preliminary
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Conclusion

• ABC effect due to narrow s -channel resonance
  with
• ABC resonance
• eigenstate in isoscalar pn and ?? systems
• can not originate from coherent production on
  deuteron
• robust enough to survive in nuclear medium
• More than just a ?? state ?
• Is it a genuine dibaryon?
• Is it a member of dibaryonic multiplet?

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Multiplet
Y(??)2 I(??)0
??
??
??
??
Kim Maltman, Nucl. Phys. A501 (1989) 843
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Outlook

• 1.0 GeV ,1.2 GeV ,1.4 GeV done
• Finalization of the data to be done
• Perform Partial Wave Analysis (JPC)
• Do we need polarization?
• Analysis of is on the way
• Analysis of to be started
• Measure
• Measure pn elastic scattering

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Thank you
39
Total x-section
?? mass
preliminary
d?? threshold