Systematic study of two-pion production in NN collisions – from single-baryon to di-baryon excitations T. Skorodko, Physikalisches Institut, Univ.Tubingen

Content * NN→NN  * NN→d   +  -,  0  0 production at T p < 1.0 GeV: Roper resonance * Summary Theoretical and experimental situation  0  0,  +  + production at T p > 1.0 GeV: ,  (1600) isospin decomposition d  +  0 production at T p = 1.1 GeV: , no ABC effect d  0  0 production at T p > 1.0 GeV: , ABC effect Motivation

WASA 4  detector

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

Theory ↔ Experiment N * →N(  ) I=0 N * →   pp→pp  +  - pp→pp  0  0 N * →N(  ) I=0 N * →  

Theory ↔ Experiment pp→nn  +  +  pp→pn  +  0

 0  0 production at T p < 1 GeV Valencia model A(tot)  A(N * →N  )+A(N * →  ) T p =0.775 GeV T p =0.895 GeV At Roper mass M=1440 MeV

 +  - production at T p = 0.8 GeV S. Abd El-Bary at el.,Eur.Phys.J. A 37(2008) 267 (COSY-TOF)

Decay branchings of Roper  -decay R=  (N * →  →N  )/  (N*→N  →N  ) N * mass [MeV] CELSIUS-WASA ** PDG Bonn-Gatchina * 0.28(3) 1.0(1) 4(2) 0.9(1) * Partial Wave Analysis γp→p  0  0  N→  N γp→p  0  - p→ n  0  0 A. Sarantsev et al., Phys. Lett. B 659(2008) 94 ** T.Skorodko et al., Eur. Phys. J. A 35(2008) 317

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

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

pp→pp  0  0 T p = 1 GeVT p = 1.1 GeV Valencia calculations with readjusted N * →  branch Valencia calculations with total Roper contribution reduced according to isospin decomposition

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

Conclusions I  The main  isoscalar production mechanism is the Roper excitation and its decay  The branching ratio of the Roper decays N * →N  /N * →  at a pole mass of 1371 MeV is 4:1  This result is in favor of a monopole mode interpretation of the Roper excitation  According to the isospin decomposition the energy dependence of the Roper total cross section behaves like a s-channel excitation  Description of the  +  + production data both in total and differential cross sections requires additional contribution from a resonance with isospin 3/2. A good candidate is  (1600)

From unbound to bound system: ABC effect

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

ABC and ΔΔ models T.Risser, M.D. Shuster, Phys.Lett. B 43, 68(1973) F.Plouin et all, Nucl.Phys. A 302(1978) 413

pn→d  0  0 T p =1.03 GeV T p =1.36 GeV conventional  calculation M.Bashkanov et al., Phys.Rev.Lett. 102(2009),

Total cross section M.Bashkanov et al., Proc. PANIC09, 239

pn→d  0  0 T p =1.03 GeV T p =1.36 GeV  calculation with a s-channel resonance  calculation without a s-channel resonance M.Bashkanov et al., Phys.Rev.Lett. 102(2009),

Crucial test of t-channel  : pp→d  +  0

pp→d  +  0 at T p =1.1 GeV ( S=2.36 GeV)  calculations for iso- scalar channel  calculations for iso- vector channel F.Kren et al., Int.J.Mod.Phys. A 24(2009), 561

Total cross section  (t-channel) F.Kren et al., nucl-ex/ J.Bystricry et al. F.Shimizy et al. CELSIUS-WASA

Conclusion II pn→d  0  0 - ABC effect: isoscalar s-channel resonance with M ABC  2M  - 90 MeV  ABC  50 MeV << 2   pp→d  +  0 - no ABC effect:  t-channel excitation

Thank you

conventional t-channel  model ANKE ‘ABC’ data

Total xsection 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 

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

Theory ↔ Experiment pp→nn  +  +  pp→pn  +  0 

Theory ↔ Experiment N * →N(  ) I=0 N * →  pp→pp  +  - pp→pp  0  0 N * →N(  ) I=0 N * →  

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

 0  0 production at T p > 1 GeV original Valencia calculations

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

Spin of ABC effect L=0

     production → Roper ansatz T p =0.75 GeV Phys.Rev.Lett. 88, (2002) N * → Nσ N * → Δ  N*N* ΔΔ NσNσ N  All theoretical curves are normalized in area to the data

Event selection pp→pp     → pp4  T p =0.775 GeV T p =1.1 GeV p 1 angle lab p 2 angle lab  angle lab Central Detector

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

Experimental evidence for a „narrow“ Roper  p →  4.2 GeV (Saturne) J J/   → N N* and N N* (BES) M Roper = 1358 MeV  Roper = 179 MeV M Roper = 1390 MeV  Roper = 190 MeV

pp (WASA) pp → pn   1.3 GeV (WASA) Experimental evidence for a „narrow“ Roper M N* =1380 MeV, Γ=180 MeV

T p =0.895 GeV Interference between Roper and ΔΔ

M 121  in 4 times bigger  cross section in pp  0  0  no contribution from 

M 121  in 4 times bigger  cross section in pp  0  0  no contribution from 

cosφ  +1

pp → pn  0  +  prediction