CELSIUS-WASA,WASA-at-COSY: two-pion production in NN collisions T. Skorodko, Physikalisches Institut, Univ.Tubingen

Content * CELSIU-WASA * WASA-at-COSY pp→pp  +  -- pp→pn  +  0 I=0,1  ? pp→pp  0  0 pp→nn  +  + I=1  T p =0.75 – 1.4 GeV T p = 1.2 GeV, deuteron target pn→pn  0  0 (in progress) pn→pp  --  0 Roper, ,  (1600) T d = 2.27 GeV, proton target ValenciamodelValenciamodel

WASA 4  detector

pp→pp  +  - pp→pp  0  0 pp→nn  +  + THEORYTHEORY EXPERIMENTEXPERIMENT N * → N  N * →   pp→pn  +  0 

NN→NN  : Valencia model L.Alvarez-Ruso et al., Nucl.Phys. A 633(1998) 519

 0  0 production at T p < 1 GeV Valencia model A(tot)  A(N * →N  )+A(N * →  ) T p =0.795 GeV COSY-TOF agree with Bonn-Gatchina result, A.Sarantsev et al., Phys.Lett. B 659(2006) 94 T p =0.895 GeV All theoretical curves are normalized in area to the data

 0  0 production at T p > 1 GeV VC with readjusted N→  branch T p = 1 GeVT p = 1.1 GeVT p = 1.2 GeVT p = 1.3 GeV All theoretical curves are normalized in area to the data

Isospin decomposition T. Skorodko et al., Phys. Lett. B 679(2009), 30

Cross section pp → nn    

Total cross section M 121

pp→pp  0  0 pp→pp  +  - ?  N * →  N * → N  Theory  Experiment : (  ) I=0

Total cross section M 121 M 101 cosφ=1

 production at T p > 1.2 GeV pp→pp  +  T p =1.36 GeV pp→pp  0  T p =1.3 GeV Valencia calculations

T p =0.895 GeV Interference between Roper and ΔΔ

M 121 M 101 M 101 (N * ) Total cross section N* (Valencia)  (Valencia) cosφ=1 T. Skorodko et al., Phys. Lett. B 679(2009), 30

Cross section pp → nn     CELSIUS/WASA  excitation experiment 

 +  +  I=2  (1232)  (1600) very small amplitude according to Valencia model M  =1500─1700 MeV  threshold energy  threshold energy    =200─400 MeV  can contribute at low energy Additional resonance with I=3/2

pp → nn      p  MeV Valencia predictions  +  (1600)

pp→pn  +  0 

 0  0 production at T p > 1 GeV VC with readjusted N * →  branch VC with readjusted total N * strength (T. Skorodko et al., Phys.Lett. B 679 (2009) 30) T p = 1 GeVT p = 1.1 GeVT p = 1.2 GeVT p = 1.3 GeV

 0  0 production at T p > 1 GeV modification of the  excitation  include relativistic corrections  reduce the contribution from ρ-exchange in  excitation by an order of magnitude (Xu Cao et al., nucl-th: ) T. Skorodko et al., Phys.Lett. B 695 (2011) 115

 0  0 production at T p > 1 GeV VC with readjusted N→  branch VC with readjusted total N * strength VC with readjusted total N * strength and with modified  excitation T p = 1 GeVT p = 1.1 GeVT p = 1.2 GeVT p = 1.3 GeV

Total pp→pp  0  0 cross section VC with readjusted total N * strength and with modified  excitation original VC VC with readjusted N→  branch VC with readjusted total N * strength

modified’ Valencia model (without readjustment N * strength) modified Valencia model

modified’ Valencia model (without readjustment N * strength) modified Valencia model modified Valencia model + ABC resonance

WASA-at-COSY data : I=0,1

* double-pionic fusion pn→d  0  -0 pd→He 3  0  0 dd→He 4  0  0 I   0 excess energy at maximum: Q ≈ 0.22 GeV ABC effect

We have data at T p = 1.2 GeV  excess energy Q : 0.17 – 0.35 GeV pn→R→    0 d00d00 pn  0  0 pp  -  0 I   no ABC effect, but resonance ? prediction Faldt & Wilkin PLB 701 (2011) 619

▲ Brunt □ Dakhno ■ KEK L.Alvarez-Ruso et al., Nucl.Phys. A 633(1998) 519  N * →  non resonant  [  b] T p [MeV] pn→pp  -  0 full Valencia calculations

Total cross section KEK NIROD at RAL Gathina WASA-at-COSY N * →   original Valencia model modified Valencia model modified Valencia model + d * d*d*

preliminary modified Valencia model + d * modified Valencia model

preliminary modified Valencia model + d * modified Valencia model

preliminary modified Valencia model + d * modified Valencia model

p p n n d * 03 d * 12      + d d M.Platonova and V.Kukulin arXiv: [nucl-th]

cos(p) cm preliminary modified Valencia model + d * modified Valencia model

cos(  - ) cm preliminary modified Valencia model + d * modified Valencia model

pn→pp  -  0 : no significant indication of ABC effect in differential cross sections total cross sections can be described by the modified Valencia model with the additional excitation of the d * resonance invariant mass M pp requires p-wave between two protons in addition to the  vertex form factor (was introduced for the description of the ABC effect)

Theory ↔ Experiment pn→pn  0  0 (np s ) + p at T d =2.27 GeV TpTp ABC

modified’ Valencia model (without readjustment N * strength) modified Valencia model modified Valencia model + ABC resonance (same strength, as in d      modified Valencia model + ABC resonance (half of strength, as in d     

Thank You

pn→R→    0 d00d00 pn  0  0   form factor

pp → nn      p  MeV Valencia predictions  +  (1600)

Particle identification (Central Detector) Momentum vs deposited energy in Plastic Barrel Energy deposited in CsI vs deposited energy in Plastic Barrel Momentum vs deposited energy in CsI

Particle identification   → 2    s)    reconstruction from  detection proton identification: dE/E method 2    identification M  p

T p =0.895 GeV Interference between Roper and ΔΔ