Study of few-body problems at WASA Wasa-at-Cosy

Content General overview General overview –  decays – dd   0 –  -mesic helium The ABC effect The ABC effect – d  – 

See talk A. Winnemoeller Friday 18:40

The ABC effect

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

pn  d  0  0

2D x-section

Total x-section pn  d  +  - pn  d  0  0  (  +  0 )=  (I=1)  (  +  - )=0.5  (I=1)+2  (I=0)  (  0  0 )=  (I=0)=0.2  (I=1) pp  d  +  0 t - channel 

Total x-section d  threshold  mass

Total x-section d  threshold  mass

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

Total xsection slices: qualitative description

Dalitz plot (peak region)

pn  d  0  0 and pp  d  +  0 (p-spectator)(n-spectator)

 +  0 invariant mass T p  1GeV pp  2 He     pp  d    

ABC in 3 He

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

dd  4 He      Invariant Mass     GeV 0.9 GeV 1.05 GeV See talk A. Pricking Tuesday 17:30

Conclusion Conclusion ABC effect due to narrow s -channel resonance with ABC effect due to narrow s -channel resonance with – – – More data next year More data next year –  -decays –dd   0 –dd  (  )  3He+N+ 

  *  * 

Outlook Finish data analysis Finish data analysis Perform Partial Wave Analysis (J PC ) Perform Partial Wave Analysis (J PC ) –Do we need polarization? 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 Kim Maltman, Nucl. Phys. A501 (1989) 843

Data analyzed so far Tp = 1.0 GeV : 70 kEvents(80%) Tp = 1.0 GeV : 70 kEvents(80%) Tp = 1.1 GeV : Tp = 1.1 GeV : Tp = 1.2 GeV : 26 kEvents(15%) Tp = 1.2 GeV : 26 kEvents(15%) Tp = 1.3 GeV : Tp = 1.3 GeV : Tp = 1.4 GeV : 47 kEvents(25%) Tp = 1.4 GeV : 47 kEvents(25%)

Angular distribution (in the peak)

Dalitz plot

Additional corrections and cross-checks

Angular distribution (in the peak)

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

Corrections for Fermi-motion

Cross-checks at pn  d  0  0  0  d  CW: pn  d  000000000000 WaC: pn  d  0  0  0

Check of resolution 3  0 PS

Resolution In pn  d  0  0  0 the  width  30MeV In pn  d  0  0  0 the  width  30MeV From MC, X-section resolution in pn  d  0  0  30MeV From MC, X-section resolution in pn  d  0  0  30MeV

pn  d  0  0 and pp  d  +  0 (p-spectator)(n-spectator)

pp  d  +  0 analysis

 +  0 invariant mass

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