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Electroexcitation of the Roper resonance from CLAS data

Electroexcitation of the Roper resonance from CLAS data. Inna Aznauryan, Volker Burkert Jefferson Lab N * 2007, Bonn, September 7, 2007. Outline. Introduction: Puzzles of the Roper resonance Analysis: Dispersion Relations and Unitary Isobar Model

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Electroexcitation of the Roper resonance from CLAS data

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  1. Electroexcitation of the Roper resonance from CLAS data Inna Aznauryan, Volker Burkert Jefferson Lab N* 2007, Bonn, September 7, 2007

  2. Outline • Introduction:Puzzles of the Roper resonance • Analysis: Dispersion Relations and Unitary Isobar Model • Results:Helicity amplitudes for γ*p→ P11(1440) • Discussion: What do we learn about the nature of the P11(1440) from these results • Summary • Comment on claims of a new P11(1650) resonance seen in nη and not seen in pη photoproduction.

  3. SU(6)xO(3) Classification of Baryons P11(1440)

  4. Introduction: Puzzles of the Roper resonance • The state attracted special attention since its discovery because of its unexpectedly low mass. • In the quark and bag models, assumption that P11(1440)≡[56,0+]r led to: • large mass difference between nucleon and P11(1440), which is several hundred MeV higher that the observed mass difference • recent qLQCD simulations show even a much larger mass for first excited state of the nucleon • wrong mass ordering between P11(1440) and S11(1535) states • Non-relativistic CQMs cannot explain sign of photo- coupling amplitude A1/2 (S. Capstick, I. Aznauryan)

  5. Introduction(continued) However, right mass ordering between P11(1440)≡ [56,0+]r and S11(1535) was observed in later investigations: • Chiral constituent QM with Goldstone-boson exchange between quarks Glozman, et al., Phys.Rep. 268, 263 (1996) • in Lattice QCD Mathur, et al., Phys.Lett. 605, 137 (2005) …. but see talk by C. Gattringer

  6. Introduction (continued) • Difficulties in the description of P11(1440) prompted the development of alternative descriptions of this state: • a q3G hybrid baryon state • a dynamically generated πN resonance • a nucleon-sigma molecule • The results for γ*p→ P11(1440) extracted from experiments in a wide Q2 range will allow us to discriminate between different descriptions of the state. • Due to the lack of predictions from the P11(πN) and P11(Nσ) resonance models we can compare only with the P11(q3G) model

  7. Analysis: CLAS data • Newep→eπ+n electroproduction data Q2=1.72,2.05, 2.44, 2.91, 3.48, 4.16 GeV2 W=1.15-1.70 GeV • Differential cross sections • Longitudinally polarized electron beam asymmetry • Data have nearly full coverage in nπ+ cm system for cosθ* and φ* > 33,000 differential cross sections, and > 3,000 electron beam asymmetries

  8. Analysis: Dispersion relations and Unitary Isobar Model • Using two approaches allows us to draw conclusions on the model dependence of the extracted results. • The main uncertainty of the analysis is related to the real parts of amplitudes which are built in DR and UIM in conceptually different way:

  9. Analysis (continued) • The imaginary parts of the amplitudes are determined mainly by the resonance contributions: • For all resonances, except P33(1232), we use relativistic Breit-Wigner parameterization with energy-dependent width (Walker, PR 182 (1969) 1729) • Combination of DR, Watson theorem, and the elasticity of t1+3/2(πN ) up to W=1.43 GeV provide strict constraints on the M1+3/2,E1+3/2,S1+3/2 multipolesof the P33(1232) (Δ(1232)).

  10. Fixed-t Dispersion Relations for invariant Ball amplitudes (Devenish & Lyth) γ*p→Nπ Dispersion relations for 6 invariant Ball amplitudes: Unsubtracted Dispersion Relations (i=1,2,4,5,6) Subtracted Dispersion Relation

  11. Analysis: Some points which are specific to high Q2 • From the analysis of the data at different Q2 = 1.7-4.2 GeV,we have obtained consistent results for fsub(t,Q2) • fsub(t,Q2) has relatively flat behavior, in contrast with π contribution:

  12. Analysis:some points which are specific to high Q2(continued) • The background of UIM we use at large Q2 consists of the Born term and t-channel ρ and ω contributions • At high Q2, a question can arise if there are additional t-channel contributions, which due to the gauge invariance, do not contribute at Q2=0, e.g. π(1300), π(1670), scalar dipole transitions for h1(1170), b1(1235), a1(1260) … • Such contributions are excluded by the data.

  13. Analysis (continued) • Fitted parameters: amplitudes corresponding to: P33(1232), P11(1440) , D13(1520) , S11(1535) F15 (1680) • Amplitudes of other resonances, in particular those with masses around 1700 MeV, were parameterized according to the SQTM or the results of analyses of previous data • Including these amplitudes into the fitting procedure did not change the results

  14. Results: Examples of cross sectionsat Q2=2.05 GeV2 • φ-dependence at W=1.43 GeV • W-dependence

  15. Results: Legendre moments for σT+ε σL Q2 = 2.05 GeV2 DR w/o P11(1440) ~cosθ ~(1 + bcos2θ) ~ const. DR UIM

  16. Results:Multipole amplitudes for γ*p→π+n Q2 =2.05 GeV2 Q2 =0 • At Q2=1.7-4.2, resonance behavior is seen in these amplitudes more clearly than at Q2 =0 • DR and UIM give close results for real parts of multipole amplitudes Im Re_UIM Re_DR

  17. CLAS Nπ, Nππ Nπ RPP Model uncertainties due to N, π, ρ(ω) → πγ form factors Results:Helicity amplitudes for the γp→ P11(1440) transition DRUIM

  18. Comparison with quark models P11(1440)≡[56,0+]r • With increasing Q2, the proper treatment of relativistic effects becomes very important • The consistent way to realize relativistic calculations of γN→N* transitions is to consider them in LF dynamics • In LF calculations, the diagrams that violate impulse approximation are removed • In the nonrel. approach of Cano et al., these diagrams are found using VDM and the 3P0 model

  19. Discussion: LF quark model predictions P11(1440)≡[56,0+]r • LF CQM predictions have common features, which agree with data: • Sign of A1/2 at Q2=0 is negative • A1/2 changes • sign at small Q2 • Sign of S1/2 is • positive • 1.Weber, PR C41(1990)2783 2.Capstick..PRD51(1995)3598 • 3.Simula…PL B397 (1997)13 4.Riska..PRC69(2004)035212 • 5.Aznauryan, PRC76(2007)025212 6.Cano PL B431(1998)270

  20. previous data previous data g Discussion:P11(1440) as a hybrid baryon? q3 G Suppression of S1/2 has its origin in the form of vertexγq→qG. It is practically independent of relativistic effects Z.P. Li, V. Burkert, Zh. Li, PRD46 (1992) 70 In a nonrelativistic approximation A1/2(Q2) and S1/2(Q2)behave like the γ*NΔ(1232) amplitudes.

  21. Summary • We have extracted transverse and longitudinal amplitudes of the γ*p→ P11(1440) transition from experimental data at high Q2 using the nπ+ final state. • The DR analysis and the UIM analysis give consistent results • The results rule out the description of the P11(1440) as a q3G hybrid state due to the strong longitudinal response obtained from the experiment for γ*p→ P11(1440)

  22. Summary (continued) • Comparison with quark model predictions provide evidence in favor of the P11(1440)as a radial excitation of the nucleon • Final confirmation of this conclusion requires a complete, and simultaneous description of the nucleon form factors and the γ*p→ P11(1440) amplitudes

  23. Evidence for a P-wave resonance near 1700 MeV in ηelectroproduction with CLAS Volker Burkert Jefferson Lab N* 2007, Bonn, September 7, 2007

  24. CLAS Q2 dependence of the S11(1535) photocoupling and evidence for a P-wave resonance in η electro-production from protons. We heard several times that the γn→nη, data show peak structure at 1650-1680 MeV, and γp→ηp did not show this structure. A new resonance is claimed that couples only to neutrons and not to protons: talks by: H. Shimizu, V. Kuznetsov, and others. CLAS collaboration has recently published data on electroproduction of ep→epη. H. Denizli et al. (CLAS), Phys. Rev. C 76, 015204 (2007), arXiv:0704.2546 [nucl-ex] Integrated cross section shows peak structure near W=1.7 GeV or/and dip structure near W=1.66 GeV.

  25. Response Functions and Legendre Polynomials Expansion in terms of Legendre Polynomials 4 resonance fit gives reasonable description including S11(1535), S11(1650), P11(1710), D13(1520) Sample differential cross sections for Q2=0.8 GeV2, and selected W bins. Solid line: CLAS fit, dashed line: η-MAID.

  26. 1.6 1.7 1.8 1.6 1.7 1.8 1.6 1.7 1.8 1.6 1.7 1.8 1.6 1.7 1.8 CLAS S-wave dominance and s-p wave interference in ep→epη Using only S11 and P11 partial waves the cross section can be qualitatively described. The observation is consistent with a rapid change in the relative phase of the E0+ and M1- multipoles because one of them is passing through resonance. • S11(1535) is seen in angle-independent term A0, at all Q2. • A1/A0 shows existence of P-wave strength interfering with the dominant s-wave. Good fit achieved with P11(1710) with Γ=100 MeV, and: ξP11(1710) /ξS11(1535) =0.22.

  27. Conclusions on γ*p→ P11(~1700) • P-wave is needed to fit the data. Interference with S11 shows resonance near 1650 MeV in η production off proton. • In a 4 resonance fit of S11(1535), D13(1520), S11(1650) and P11,a reasonable fit is obtained with P11 mass M ~ 1650 MeV, width Γ=100 MeV. • There is no need for a new P11 state as long as P11(1710) parameters (mass, width, bηp) are not well established. Abstract of publication: “A sharp structure is seen near W ~ 1.7 GeV. The shape of the differential cross section is indicative of the presence of a P-wave resonance that persists to high Q2.”

  28. CLAS Q2 dependence of the S11(1535) photocoupling and evidence for a P-wave resonance in η electro-production from protons. We heard several times that the γn→nη, data show peak structure at 1650-1680 MeV, and γp→ηp does not show this structure. A new resonance is claimed that couples only to neutrons and not to protons: talks by: H. Shimizu, V. Kuznetsov, …. CLAS collaboration has recently published data on electroproduction of ep→epη. H. Denizli et al. (CLAS), Phys. Rev. C 76, 015204 (2007), arXiv:0704.2546 [nucl-ex] Integrated cross section shows peak structure near W=1.7 GeV or/and dip structure near W=1.66 GeV.

  29. Response Functions and Legendre Polynomials Expansion in terms of Legendre Polynomials 4 resonance fit gives reasonable description: S11(1535), S11(1650), P11(1710), D13(1520) Sample diff. cross sections for Q2=0.8 GeV2, and selected W bins. Solid line: CLAS fit, dashed line: η-MAID.

  30. 1.6 1.7 1.8 1.6 1.7 1.8 1.6 1.7 1.8 1.6 1.7 1.8 1.6 1.7 1.8 CLAS S-wave dominance and s-p wave interference in ep→epη Using only S11 and P11 partial waves the cross section can be qualitatively described. The observation is consistent with a rapid change in the relative phase of the E0+ and M1- multipoles because one of them is passing through resonance. • S11(1535) is seen in angle-independent term A0, at all Q2. • A1/A0 shows existence of P-wave strength interfering with the dominant s-wave. Good fit achieved with P11(1710) with Γ=100 MeV, and: ξP11(1710) /ξS11(1535) =0.22.

  31. Conclusions on γ*p→ P+11(1650) • P-wave is needed to fit the data. Interference with S11 clearly shows resonance near 1650 MeV in η production off proton. • In a 4 resonance fit of S11(1535), D13(1520), S11(1650), and P11 a good fit is obtained with mass M ~ 1650 MeV, width Γ=100 MeV. • No need for a new P11 state as long as P11(1710) parameters (mass, width, bηp) are not well established. All of this has been published

  32. Single Quark Transition Model Predictions for [56,0+]→[70,1-] Transitions Proton

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