Double-Pionic Fusion in Nucleon Collisions on Few Body Systems - The ABC Effect and its Possible Origin Wasa-at-Cosy Celsius Wasa

First step into the ABC Alexander Abashian, Norman E. Booth and Kenneth M. Crowe, Phys. Rev. Lett. 5, 258 (1960) Alexander Abashian, Norman E. Booth and Kenneth M. Crowe, Phys. Rev. Lett. 5, 258 (1960) π 2 π Phase Space inclusive

All of ABC No ABC effect! ABC effect

ΔΔ ΔΔ Large π π invariant mass Small π π invariant mass π N Δ π N Δ π N Δ π N Δ p n Δ Δ d π π

F. Plouin et. al. Nucl. Phys. A302 (1978), ABC and ΔΔ models π π π π π π  F. Plouin, P. Fleury, C. Wilkin PRL 65 (1990) 692

Results from new exclusive measurements

WASA 4  Detector   3 He/d    COSY/

What we actually did p n p

p d      

Total xsection pn  d  +  - pn  d  0  0 Tp = 1.0 GeVTp = 1.2 GeVTp = 1.4 GeV  (  +  0 )=  (I=1)  (  +  - )=0.5  (I=1)+2  (I=0)  (  0  0 )=  (I=0)=0.2  (I=1) pp  d  +  0

Total x-section d  threshold  mass

2D x-section

Qualitative description n p n Δ Δ d π π + Δ Δ d π π p

Total xsection slices: qualitative description

M.Bashkanov et. al, Phys. Lett. B637 (2006) (I=0,1) (I=0) pd  3 Heππ, T p =0.89 GeV

Conclusion ABC effect due to narrow S-channel resonance with ABC effect due to narrow S-channel resonance with – – – ABC resonance: ABC resonance: – eigenstate in isoscalar pn and  systems – robust enough to survive in nuclear medium More than just a  state ? More than just a  state ? –Is it a genuine dibaryon?

Outlook Finish data analysis Finish data analysis Perform Partial Wave Analysis (J PC ) Perform Partial Wave Analysis (J PC ) Analysis of Analysis of Measure Measure Measure pn elastic scattering Measure pn elastic scattering

Multiplet 10  10=35  28  27  10   *  *+  *  *  +  *  * Y(  )=2 I(  )=0

  *  * 

Dalitz plot

Total xsection slices: qualitative description

Parameters of a new state M R = GeV  = 53 MeV

Total x-section Tp = 1.0 GeV Tp = 1.2 GeV Tp = 1.4 GeV

ΔΔ versus Δ pd  3 Heππ, T p =895 MeV

ΔΔ ΔΔ π N Δ π N Δ π N Δ π N Δ Large π π invariant mass Small π π invariant mass

pn  dππ, T p =1.03 GeV

M.Bashkanov et. al, Phys. Lett. B637 (2006) (I=0,1) (I=0) pd  3 Heππ, T p =0.89 GeV

ΔΔ Resonance p n p n Δ Δ d π π Δ Δ d π π +

ΔΔ resonance in differential distributions Δ Δ π π Δ π π Δ Δ π π Δ + Parameter of F(q) is fitted here pd  3 Heππ q ΔΔ  q 

ΔΔ resonance parameters

Consistent description for d and 3 He case With ΔΔ resonance Without ΔΔ resonance pd  3 He  pn  d  T p =0.895 GeV T p =1.03 GeV T p =1.35 GeV

Angular distributions ΔΔ bound ΔΔ peak full pd  3 He  T p =0.895 GeV

Angular distributions ΔΔ bound ΔΔ pn  d  T p =1.03 GeV

Quantum numbers of the resonance From Fermi-statistics: J=1 +,3 + if L ΔΔ =0 3 S 1   (  d ) : S wave only 3 D 1   (  d ) : S + D waves 3 D 3   (  d ) : no S wave pn  R  d  0  pn  d  0  0 pn  d  0  0 I=0,1I=0I=0,2 I=0

pp  d  +  0  no ABC  * (k 1 x k 2 )  T p =1.1 GeV Control channel (NO ABC expected)

Data collected for pn  d  0  0 T p =1.0, 1.1, 1.2, 1.3, 1.4 GeV T p =1.0, 1.1, 1.2, 1.3, 1.4 GeV To cover full resonance region To cover full resonance region To have overlaps between different energies, due to Fermi To have overlaps between different energies, due to Fermi To reduce systematical errors. To reduce systematical errors.

Results from dd   +X beamtime Collected energies: T d = 0.8, 0.9, 1.01, 1.05, 1.117, 1.2, 1.25, 1.32, 1.4 GeV

Phase shifts pn  pn Elastic scattering

Outlook Wasa-at-Cosy Wasa-at-Cosy Nov07-Dec07 dd runs Nov07-Dec07 dd runs Feb08 pd runs Feb08 pd runs

ΔΔ - FSI

Energy dependence of the low-mass enhancement unbound (ΔΔ) bound ΔΔ 27 MeVbound (ΔΔ) 27 MeV

FSI p n p n   p n   n n p n p n p n p p n    d p n     d p n      d p n    … +++…

3 S 1 phase shifts

3 D 3 phase shifts

ΔΔ resonance parameters

Effect of collision damping Without collision damping With collision damping

Δ resonance π N Δ π N Δ π N Δ L=1

Total x-section for ΔΔ resonance ABC channels (I=0) No ABC (I=1)

First step into the ABC Alexander Abashian, Norman E. Booth and Kenneth M. Crowe, Phys. Rev. Lett. 5, 258 (1960) Alexander Abashian, Norman E. Booth and Kenneth M. Crowe, Phys. Rev. Lett. 5, 258 (1960) π 2 π Phase Space

All of ABC No ABC effect! ABC effect

Δ resonance π N Δ π N Δ π N Δ L=1

F. Plouin et. al. Nucl. Phys. A302 (1978), ABC and ΔΔ models π π π π π π  F. Plouin, P. Fleury, C. Wilkin PRL 65 (1990) 692

ΔΔ versus Reality

Total x-section for ABC channels (I=0) No ABC (I=1) pp  d  +  0

NΔ state in pp  + d  pp

Total x-section for ABC channels (I=0) No ABC (I=1) pp  d  +  0