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Study of N* excitations in 2-pion production

Study of N* excitations in 2-pion production. Analysis of p + p - p single differential cross-sections. Isobar Model JM05. V. Mokeev. g p  p - D ++. g p  p + D 0. g p  p + D 13 (1520). g p  r p. g p  p - P ++ 33 (1600). g p  p + F 0 15 (1685). direct 2 p production. JM06.

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Study of N* excitations in 2-pion production

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  1. Study of N* excitations in 2-pion production

  2. Analysis of p+p-p single differential cross-sections. Isobar Model JM05 V. Mokeev gpp-D++ gpp+D0 gpp+D13(1520) gprp gpp-P++33(1600) gpp+F015(1685) direct2p production JM06

  3. Test of JM05 program on well known states. ep → epp+p- A3/2,GeV-1/2 (A1/22+S1/22)1/2, GeV-1/2 D13(1520) Q2 GeV2 Q2 GeV2 → JM05 works well for states with significant Npp couplings.

  4. P11(1440) and D13(1520) electrocouplings from Np and pπ+π- P11(1440) D13(1520) from analysis of 1p CLAS data from analysis of CLAS 2p data within JM06 combined analysis of 1p/2p CLAS data • 2p data show clear evidence for sign flip of P11(1440) A1/2 electrocoupling. • Electrocouplings obtained in two independent analyses of 1p and 2p channels are in reasonable agreement.

  5. First consistent amplitudes for A1/2(Q2), A3/2(Q2) of D33(1700) Many of the higher mass states have significant coupling to Nππ. State has dominant coupling toNpp : PDG:80-90% Np: (10-20)% ep → epp+p- D33(1700)

  6. Search for New Baryon States

  7. Quark models with underlying SU(6)xO(3) symmetry predict many states, not observed in either hadronic experiments or in meson photo- and electro-production. Possible solutions: 1. States don’t exist, e.g. di-quark model predicts fewer states, with different underlying symmetry group |q2q> 2. States exist but have not been found. |q3> “Missing” Baryon States Possible reason: they have small coupling to pN-channel. • Model expectations:Hadronic couplings toNpp(Dp, Nr) much larger, while photocouplings are more comparable to those for observed states. Other channels that may be sensitive to “missing” states are: KL, KS, pw

  8. Evidence for new baryon states? - Is the P33(1600)*** is really there? - One more 3/2+(1720) state ? - New resonances in KY ?

  9. Search for Baryon States ingp pp+p - • Two methods: • Isobar models (similar approach as in single pion analysis): • energy-dependences of amplitudes are parameterized. • fits to several (or all) one-dimensional projections. • Event-by event analysis: • fit partial-wave content independently for every energy bin. • makes maximum use of all correlations in the multi-dimensional phase space. • ambiguities can give multiple solutions.

  10. SU(6)xO(3) Classification of Baryons P33(1600)

  11. Evidence for P33(1600) *** state g p pp +p - W=1.59 GeV Sample data Fit to high statistics photoproduction data requires inclusion of P33(1600) state. no P33(1600) with P33(1600)

  12. P33(1600) state parameters world this analysis

  13. A new 3/2+(1720) baryon state? • epp +p - ep • JM03 Isobar Model Analysis Contributions from conventional states only Fit with new 3/2+(1720) state M.Ripani et. al. Phys. Rev. Lett.91, 022002 (2003) Difference between curves due to signal from possible 3/2+(1720) state

  14. Photo- and electroproduction comparsion pp +p - electroproduction photoproduction Q2=0 Q2=0 W(GeV) W(GeV)

  15. Totalgppp +p -cross-section off protons. no 3/2+ full calculation Background Resonances Interference • Hadronic couplings and mass derived from the fit of virtual photon data, and 3/2+(1720) photocouplings fitted to the real photon data. • Signal from 3/2+(1720) state present, but masked by large background and destructive N*/background interference.

  16. Parameters derived from combined analysis Mass and decays

  17. Search for CQM predicted states. CLAS • To reduce ambiguities, the search for new excited states aims at “complete” or nearly complete measurements in γp→πN, ηN, K+Y and γn→πN, K0Y and using combinations of beam, target, and recoil polarizations: • differential cross sections with unpolarized, circularly polarized, and linearly polarized photon beams, • recoil polarizations for hyperons, • longitudinally or transversely polarized proton and neutron (deuteron) targets. • Other reactions include γp → ρN, ωp, ππN with linearly polarized beams, and with polarized beam and polarized targets.

  18. New Results in γp→pπ0 CLAS FA06 solution of SAID analysis • A1/2 from Nπ analysis for • S11(1535) now agrees with Nη results as was found earlier in electro-production. • Strong excitation of P13(1720) is consistent with earlier analysis of pπ+π- electro-couplings.

  19. Photoproduction of K+Λ, K+Σ0 P11 K exchange P13 CLAS P13 Fit: Bonn-Gatchina group, Anisovich et al., 2007

  20. Photoproduction of K+Λ/Σ0 Fit with P13(1900) KΛ KΣ Fit: Bonn-Gatchina group, Anisovich et al., 2007

  21. γp—>K+Λ Polarization transfer Quark-Diquark Model (E. Santopinto, 2005) Includes *** / **** states CLAS w/o P13(1900) with P13(1900) Coupled channel fit: Bonn-Gatchina group, Anisovich et al, 2007 Fit shows strong preference for second P13 state. Existence of this state would be evidence against the quark-diquark model.

  22. Excited Cascades Ξ* CLAS • Advantage over search for N*’s and Y*’s is narrow widths of Ξ’s • Possible production mechanism through decay of excited hyperons – requires large acceptance and high luminosity experiments Ξ(1320) Possible production mechanism Ξ(1530) Missing mass MM(K+K+) works for narrow states, but higher energy and higher statistics are needed.

  23. Search in γp―>π-K+K+Ξ* CLAS Ξ(1530) A Ξ state at 1.62GeV and 50 MeV width could be the 1* candidate in PDG. Such a state would be consistent with a dynamically generated Ξπstate. It would contradict quark models. Requires more statistics and PWA. New high statististics run in 2008!

  24. CLAS Experiment Status & Plans of Search for New N* States

  25. Eγ=1.5 – 1.7 Ks Λ M(π+π-), GeV M(pπ-), GeV CLAS γd→K0Λ, π-p, (ps) Eγ=1.1-1.3 GeV All polar angles < 0.1% of all data Photons produced coherently from aligned diamond crystals are linearly polarized. Online beam asymmetry for γn→π-p Identify: Ks→π+π- Λ→pπ- • Plots show a 5 GeV run with the coherent edge at 1.9 GeV

  26. γp →K+Λ → → → Projected Accuracy of Data (4 of over 100 bins)

  27. γn →K0Λ → → → Projected Accuracy of Data (4 of over 100 bins)

  28. Conclusions • The study of N* excitations in photo- and electroproduction of mesons from nucleons is key for the understanding of the strong force that confines the quarks into nucleons. • The experimental and theoretical analysis we are all engaged in will make gigantic contributions towards that goal.

  29. N*’sAREFUN !

  30. Fit of CLAS 2p data on 3 invariant masses and p- angular distributions within the framework of JM05. s, mcbn Q2=0.65 Gev2 Q2=0.95 Gev2 Q2=1.30 Gev2 W, GeV Reasonable description of invariant mass and p- angular distributions was achieved in entire kinematics area covered by CLAS data.

  31. Diquark-Quark Model (E. Santopinto, 2005) Spectrum predicted for masses below 2 GeV. Includes all observed *** & **** states

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