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Collaborators Johan Durand, CEA - Saclay Jun He, CEA - Saclay Zhenping Li, Univ. of Maryland

Collaborators Johan Durand, CEA - Saclay Jun He, CEA - Saclay Zhenping Li, Univ. of Maryland Qiang Zhao, IHEP - Beijing PLAN : Motivations Chiral constituent quark approach Results for  p → η p ; E  Lab ≈ 0.7 to 3.0 GeV  W ≈ 1.5 to 2.6 GeV  M N* Role of N*s: “known” and “New”

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Collaborators Johan Durand, CEA - Saclay Jun He, CEA - Saclay Zhenping Li, Univ. of Maryland

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  1. Collaborators Johan Durand, CEA - Saclay Jun He, CEA - Saclay Zhenping Li, Univ. of Maryland Qiang Zhao, IHEP - Beijing PLAN: Motivations Chiral constituent quark approach Results for p → ηp ; ELab ≈ 0.7 to 3.0 GeV  W ≈ 1.5 to 2.6 GeV  MN* Role of N*s: “known” and “New” Summary & concluding remarks NSTAR2007, Bonn, Sept. 5, ’07

  2. New generation of data for p ηp

  3. What do we learn from those data? • Need a formalism robust enough to • Allow embodying all known N*s (i.e. PDG, one to four star resonances) • Introduce new resonances reported by several authors S11, P11, P13, D13, D15& H1,11 • Build a model with “reasonable” number of adjustable parameters

  4. .

  5. Additional P11, D15& H1,11 resonances? • Anisovich et al., EPJ A 25 (2005) 427 ; Isobar model,γpπN, ηN: P11(1840), D15(1875) ↔ D15(2200) in PDG? • Sarantsev et al., EPJ A 25 (2005) 441 ; Isobar model, γp Κ+Λ, Κ+Σ°, Κ°Σ+: P11(1840) • Corthals et al., PRC 73 (2006) 045207 ; Regge + Resonance Approach, γp Κ+Λ: P11(1900) • Arndt et al., PRC 74 (2006) 045205, EPWA, πNπN, ηN: H1,11(2247)

  6. Present approach p → ηp Chiral Constituent Quark Model Starting point: low energy QCD Lagrangian derived by Manohar & Georgi, Nucl. Phys. B234 (1984), which ensures that the meson-baryon interaction is invariant under the chiral transformation

  7. Chiral Constituent Quark Model Chiral Constituent Quark Model

  8. SU(6)O(3) symmetry predicts: C2N* = 0 or 1 e.g. C2N* = 1 for S11(1535) & D13(1520) C2N* = 0 for S11(1650) & D13(1700) SU(6)O(3) symmetry is broken due to the configuration mixings caused by one-gluon exchange (Isgur, Karl & Koniuk, PRL 1978) Configuration mixings between two SU(6)O(3) states with the total quark spin 1/2 or 3/2: S11: N(2PM)1/2- N(4PM)1/2- D13: N(2PM)3/2- N(4PM)3/2-

  9. Configuration mixing │S11(1535) = │N(2PM)1/2- cosθS - │N(4PM)1/2-sinθS │S11(1650)  = │N(2PM)1/2- sinθS + │N(4PM)1/2- cosθS • Transition amplitudes: AN* N│Hm(│N* N*│He│N AS11 N│Hm(cosθS│N(2PM)1/2-  - sinθS│N(4PM)1/2-) (cos θSN(2PM)1/2-│- sinθSN(4PM)1/2-│)He│N  N(4PM)1/2-│He│N = 0, due to Moorhouse selection rule (PRL 1966) AS11 (cos2θS – R sinθS cosθS )N│Hm│N(2PM)1/2- N(2PM)1/2-│He│N RS = [ N│Hm │N(4PM)1/2-]/[ N│Hm │N(2PM)1/2- ] SU(6)O(3)  RS = -1 & RD = 1/√10, for p → ηp CS11(1535) = cosθS(cosθS – sinθS) CD13(1520) = cosθD(cosθD – sinθD/√10 ) CS11(1650) = - sinθS(cosθS + sinθS) CD13(1700) = sinθD(cosθD/√10 + sinθD)

  10. Ingredients s-channel: all known I=1/2 N*s & 6 “new” ones u-channel: nucleon Born term + N*s t-channel:  & ω exchanges Previous study (Eγlab ≤ 2 GeV) B. Saghai & Z. Li, EPJ A11 (2001); Limited to n ≤ 2 shell & no t-channel n = 1: 2 S11, 2 D13, 1 D15 n = 2: 2 P11, 2 P13, 2 F15, 1 F17 Present work: besides t-channel embodies also: n = 3: S11, D13, D15, G17, G19 n = 4: P11, H19 Degenerate n=5: I1,11 n=6: K1,13

  11. All I=1/2 PDG N* + 6 new ones .

  12. Full model • 21 known N*s • 6 new N*s • Fitted on 1822 data points • χ2 =1.81 • Mixing angles: θS ≈ - 35° ; θD ≈ 15° (in good agreement with findings by Isgur, Karl, Chizma, Capstick…)

  13. Differential cross-section

  14. Polarization observables

  15. Removing one resonance .

  16. “Reduced” model • Remove ALL 18 N*s (δχ2 ≤15%) • Then, re-fit the data with remaining 9 N*s χ2 =1,81 → 2,12

  17. Schematic presentation of the role played by the most relevant resonances in the process gp→ ηp

  18. Polarization observables

  19. Differential cross-section

  20. Summary & Concluding remarks (I) • Direct channel formalism for p →ηp, within a chiral constituent quark approach. • All data ford/dΩ, Σ & Tare well reproduced.  All 21 Known N*s and 6 new ones included in the model.  Rather few and severely constrained adjustable parameters.  Reaction mechanism dominated by 6N*. HOWEVER, Direct channel investigations: mandatory, but No strong conclusions!

  21. Summary & Concluding remarks (II) To go further, two directions: • Experimental: polarization asymmetries, especially with polarized target • Theoretical: coupled-channel approach (cf. talk by Harry Lee): • Already investigated by our collaboration (Argonne, Barcelona, Pittsburgh, Saclay) p → [N ; N ; KY] → K+ Λ W.-T. Chiang, B. Saghai, F. Tabakin, T.-S.H. Lee, PRC 69, 065208 (2004). B. Juliá-Díaz, B. Saghai, T.-S.H. Lee, F. Tabakin, PRC 73, 055204 (2006). • In progress J. Durand, J. He, B. Juliá-Díaz, T.-S.H. Lee, T. Sato, B. Saghai, N. Suzuki p → [N ;  ; N ; N ; ηN] → ηp

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