1 Study of N* excitations in 2-pion production

2 Analysis of  +  - p single differential cross-sections.  p  -  ++ p+0p+0 pppp  p  - P (1600)  p  + F 0 15 (1685) direct 2  production  p  + D 13 (1520) Isobar Model JM05 JM06 V. Mokeev

3 Test of JM05 program on well known states. D 13 (1520) ep → ep     (A 1/2 2 +S 1/2 2 ) 1/2, GeV -1/2 A 3/2, GeV -1/2 Q 2 GeV 2 → JM05 works well for states with significant N  couplings.

4 P 11 (1440) and D 13 (1520) electrocouplings from N  and pπ + π - from analysis of CLAS 2  data within JM06 from analysis of 1  CLAS data combined analysis of 1  CLAS data 2  data show clear evidence for sign flip of P 11 (1440) A 1/2 electrocoupling. Electrocouplings obtained in two independent analyses of 1  and 2  channels are in reasonable agreement. D 13 (1520)P 11 (1440)

5 First consistent amplitudes for A 1/2 (Q 2 ), A 3/2 (Q 2 ) of D 33 (1700) D 33 (1700) ep → ep     State has dominant coupling to N  : PDG:80-90% Np  Many of the higher mass states have significant coupling to Nππ.

6 Search for New Baryon States

7 |q 3 > |q 2 q> Possible reason: they have small coupling to  N- channel. Possible solutions: 1. States don’t exist, e.g. di-quark model predicts fewer states, with different underlying symmetry group 2. States exist but have not been found. Model expectations: Hadronic couplings to N  ( , N  ) much larger, while photocouplings are more comparable to those for observed states. Other channels that may be sensitive to “missing” states are : K , K , p  “Missing” Baryon States 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.

8

9

10 - Is the P 33 (1600) *** is really there? - One more 3/2 + (1720) state ? - New resonances in KY ? Evidence for new baryon states?

11 Search for Baryon States in  p 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.

12 SU(6)xO(3) Classification of Baryons P  (1600)

13 Evidence for P 33 (1600) *** state W=1.59 GeV no P 33 (1600) with P 33 (1600) Fit to high statistics photoproduction data requires inclusion of P 33 (1600) state. Sample data  p p    

14 P 33 (1600) state parameters Mass, MeV 1686 ± PDG 1687 ± 44 Dytman 1706 ± 10 Manley Total decay width, MeV 338 ± PDG 493 ± 75 Dytman 430 ± 75 Manley BF (  65 ± PDG 59 ± 10 Dytman 67 ± 5 Manley A 1/2 -30 ± ± 20 PDG A 3/2 -17 ± ± 20 PDG this analysis world

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

16 Photo- and electroproduction comparsion photoproductionelectroproduction p     Q 2 =0 W(GeV) Q 2 =0

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

18 Parameters derived from combined analysis Mass, MeV Total width, MeV BF(  ), % BF(  P), % “New 3/2 + State” PDG P13(1720) not observed70 – 85 Mass and decays

19 –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, K 0 Y 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. Search for CQM predicted states. CLAS

20 New Results in γp → pπ 0 CLAS FA06 solution of SAID analysis  A 1/2 from Nπ analysis for S 11 (1535) now agrees with Nη results as was found earlier in electro-production.  Strong excitation of P 13 (1720) is consistent with earlier analysis of pπ + π - electro- couplings.

21 Photoproduction of K + Λ, K + Σ 0 Fit: Bonn-Gatchina group, Anisovich et al., 2007 CLAS P13 P 11 K exchange

22 Photoproduction of K + Λ/Σ 0 Fit: Bonn-Gatchina group, Anisovich et al., 2007 KΛKΛKΣKΣ Fit with P 13 (1900)

23 γp—>K + Λ Polarization transfer w/o P 13 (1900) with P 13 (1900) CLAS Fit shows strong preference for second P 13 state. Existence of this state would be evidence against the quark-diquark model. Includes *** / **** states (E. Santopinto, 2005) Quark-Diquark Model Coupled channel fit: Bonn-Gatchina group, Anisovich et al, 2007

24 Excited Cascades Ξ* 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 CLAS Ξ(1320) Ξ(1530) Missing mass MM(K + K + ) works for narrow states, but higher energy and higher statistics are needed. Possible production mechanism

25 Search in γp―>π - K + K + Ξ* CLAS 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 Ξπ state. It would contradict quark models. Requires more statistics and PWA. Ξ(1530) New high statististics run in 2008!

26 ReactionDiffc rs Lin. beam Circ. beam Long. Target Trans. Target RecoilGroupPublication/Status/Schedule γp→pπ 0 xG1arXiv: γp→nπ + xG1analysis γp→pη xG1, G10PRL89, , 2002 γp→pη ’ xG1, G10PRL96, , 2006 γp→K + Λ, K + Σ xxxG1, G10PRC , 2004; PRC73, , 2006; PRC , 2007 γp→K 0* Σ + x G1PRC , 2007 γp→p π - π + xxG1PRL , 2006, analysis γp→pω, pρ 0, nρ + xxG82005 / Analysis γn → K 0 Λ, K 0 Σ, K + Σ-, K - Σ + xxxxG / Analysis γp→p π 0, nπ +, pη xxxxG9-FROST2007/2009 γp→ K+Λ, K+Σ xxxx xG9-FROST2007/2009 γp→p π - π + xxxx G9-FROST2007/2009 γn → K 0 Λ, K 0 Σ, K + Σ -, K - Σ + xxxx xG14-HD2010 γn →p π -,nπ + π - xx xx G14-HD2010 Experiment Status & Plans of Search for New N* States CLAS

27 CLAS  γ  d → K 0 Λ, π - p, (p s ) Eγ=1.5 – 1.7 Online beam asymmetry for γn → π - p Photons produced coherently from aligned diamond crystals are linearly polarized. Identify: K s → π + π - Λ → pπ - Eγ= GeV All polar angles < 0.1% of all data KsKs M(π + π - ), GeV Λ M(pπ - ), GeV Plots show a 5 GeV run with the coherent edge at 1.9 GeV

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

29 γn → K 0 Λ Projected Accuracy of Data (4 of over 100 bins) →→→

30 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.

31 N*’s ARE FUN !

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

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