Jefferson Lab, Newport News, VA Philip Cole Idaho State University November 1, Brief Summary on the which took place on October 13-15, 2008 at For more information, see: International Organizing Committee: V. Burkert B. Julia-Diaz R. Gothe T.-S. H. Lee V. Mokeev

Outline [Needs Work] Excited baryons Classification NΔ transition form factors Low mass N* excitations, Roper A near-threshold resonance S 11 (1535) Search for new baryon states Coupled channels analysis Summary

Electromagnetic Excitation of N*’s The experimental N* Program has two major components: 1) Transition form factors of known resonances to study their internal structure and confining potential 2) Spectroscopy of excited baryon states, search for new states. Both parts of the program are being pursued in various decay channels, e.g. Nπ, pη, pπ + π -, KΛ, KΣ, pω, pρ 0 using cross sections and polarization observables.

Electromagnetic Excitation of N*’s vv N  p   p  e e’ γvγv N N’N’ N*,△ A 3/2, A 1/2, S 1/2 M l+/-, E l+/-, S l+/-  Measure the electromagnetic excitations of low-lying baryon states (<2 GeV) and their transition form factors over the range Q 2 = 0.1 – 7 GeV 2 and measure the electro- and photo-production of final states with one and two pseudo-scalar mesons. DOE Milestone 2012 Volker Burkert

Electromagnetic Probe for Resonance Physics  N PWA constraint [No theoretical input] }  For Q 2 = 0:  For Q 2  0: () 2 Q2Q2Q2Q2 N Igor Strakovsky

The γNΔ(1232) Quadrupole Transition SU(6): E 1+ =S 1+ =0 pQCD limit pQCD limit Shape at low Q 2 Volker Burkert

Ralf Gothe

12 S 11 (1535): A near-threshold resonances S 11 (1535) in the CQM is a L 3Q =1, P=-1 state. It has also been described as a bound (KΣ) molecule with a large coupling to pη. The very slow falloff of the A 1/2 (S 11 ) form factor with Q 2 suggests a Q 3 system rather than a meson-baryon (QQQ-QQ) molecule (no form factor calculations exist for the molecular case). S 11 (1535)

Whitepaper on the Excited Baryon Program with the 12 GeV Upgrade Contributors: All who have contributed significantly Table of Contents –I. Introduction and Recent Progress –II. Experimental Developments for 12 GeV upgrade –III. Theoretical developments for 12 GeV upgrade –IV. Reaction Models for Data Analysis –V. Experiments to be proposed –VI. Acknowledgments References Final Version by: Dec 8, 2008

Focus of Theoretical Developments o Lattice QCD (R. Edwards) o Models based on Dyson-Schwinger Equations of QCD (C. Roberts) o Relativistic constituent quark models (M. Giannini) o GPD with N* (M. Polyakov) Reaction Models o Dynamical Analysis at EBAC (B. Julia-Diaz) o Isobar model analysis at Mainz (L. Tiator) o Isobar model analysis at JLab (I. Aznauryan, V. Mokeev) Experiments to be Proposed. oN  N* Transition Form Factors with CLAS at 11 GeV (Gothe, Mokeev, Burkert, Joo, Stoler, Cole) oOthers? within the context of the Whitepaper

List of the questions relating to the motivation of N* studies using an 11-GeV electron beam for probing photon virtualities from 5.0 to 10 GeV 2. 1.How will our proposed N* transition helicity amplitude data in the Q 2 region of 5.0 to 10 GeV 2 impact your theoretical approach and, in general, how will this data extend our overall understanding of strong interactions responsible in the formation of N*s? This set of 7 Questions sent to all theorists who attended the Workshop

To justify this claim of being able to access quark-core degrees of freedom at high photon virtualities, we ask you to make estimates of the Q 2 -behavior of the two components, i.e. a) constituent quark core b) meson-baryon dressing of N-N* photon vertices, A 1/2 A 3/2 S 1/2 P 33 (1232), P 11 (1440), D 13 (1520), S 11 (1535), F 15 (1685), P 13 (1720), D 33 (1700) 5.0 < Q 2 < 10 GeV 2 which contribute to the A 1/2, A 3/2, S 1/2 N-N* transition amplitudes: for the N* states: P 33 (1232), P 11 (1440), D 13 (1520), S 11 (1535), F 15 (1685), P 13 (1720), D 33 (1700) in the region 5.0 < Q 2 < 10 GeV 2. vv N  p   p  photon virtualities ranging from 5.0 to 10 GeV 2 meson-baryon dressing to the N-N* vertices are presumably small. 2.We anticipate that by studying N* behavior at photon virtualities ranging from 5.0 to 10 GeV 2, it will give us access to resonance structure at distances, where the expected contributions from meson-baryon dressing to the N-N* vertices are presumably small. Hence this probe will allow for effectively delineating the constituent quark-core configurations from other competing processes. γvγv N N*,△ A 3/2, A 1/2, S 1/2 M l+/-, E l+/-, S l+/- e e’

3. How will the data on N-N* transition helicity amplitudes, obtained at 5.0 < Q 2 < 10 GeV 2, extend our knowledge on the binding potential and effective interactions responsible for 3-quark configuration mixing (i.e. OGE, OPE, instanton,…) within constituent quark models? –How will such data on N* electrocouplings at high Q 2 help us in getting access to light-cone wave functions of excited proton states and the associated currents? –What can we learn about the evolution constituent quark form factors? –What are the prospects of relating the constituent quark, covariant and Dyson-Schwinger models to the underlying QCD and, in turn, how will this data on N* electrocouplings at high Q 2 be useful in establishing these relations? 4. Is it possible or likely that data on N* electrocouplings at high Q 2 will afford us access to excited flux tubes as a possible active degree of freedom in the N* structure? And could this be used to study flux tube self-interactions?

rapid risedressed-quark running mass 5.How does the rapid rise of the dressed-quark running mass impact the N-N* transition helicity amplitudes, as revealed from both the studies of the dressed-quark propagator within the framework of Dyson-Schwinger equations and from lattice calculations? How then may this running mass phenomenon be established in the studies of N* electrocouplings at high Q 2 ? 6. What are the prospects of having lattice calculations –which relate the underlying QCD data in N-N* helicity transition amplitudes at Q 2 up to 10 GeV 2 ? –And would such N* electrocoupling data be of significant benefit in making lattice calculations within this high Q2 regime, where the expected contributions from meson-baryon dressing of N- N* photon vertices become negligible?

7.What are the prospects of shedding light onto the unique relations among the various N-N* transition helicity amplitudes (or the N-N* transition form factors) in setting constraints on the moments of different combination of the N-N* GPDs?

  p  P 11 (1440): 3q picture with P 11 (1440) as [56,0 + ] r LF RQM: Weber, PR C41 (2783) 1990 Capstick, Keister, PR D51 (1995) 3598 Pace, Simula et.al., PR D51 (1995) 3598 Aznauryan, PR C76 (2007) All LF RQM describe sign change of A 1/2 the amplitude S 1/2 Strong evidence in favor of P 11 (1440) as a first radial excitation of 3q ground state All LF RQM fail to describe the amplitude A 1/2 at Q 2 < 1 GeV 2 Inna Aznauryan

P 11 (1440): Additional components and contributions Pion cloud EBAC (preliminary) Julia-Diaz et.al., PR C77(2008) % admixture of qqqqq components in the Roper resonance   (theory) =  (exp) : Li, Riska, PR C74(2006) Pion cloud contributions and additional qqqqq components in the Roper resonance can improve the description at small Q 2 Inna Aznauryan

P 11 (1440) as a q 3 G hybrid state Supression of S 1/2 has its origin in the form of the vertex  * q  qG ; it is practically independent of relativistic effects P 11 (1440) as q  G: Li, Burkert,Li, PR D46 (1992) 70 P 11 (1440) as a q 3 G hybrid state is ruled out !!! Inna Aznauryan

23 Helicity amplitudes of the   p  P 11 (1440) transition NN CLAS data : PDG First measurements of A 1/2 at Q 2 > 0 N  N  combined N    preliminary   p  p   M.Dugger et al., PR C ,2007 First measurements of S 1/2 Inna Aznauryan

Helicity amplitudes of the   p  D 13 (1520) transition NN CLAS data : N  N  combined N   preliminary   Old data: Bonn, DESY, NINA PDG  p  p    M. Dugger First definite results for A 1/2, A 3/2 in wide range of Q 2 First measurements of S 1/2 Inna Aznauryan

25 Helicity amplitudes of the   p  S 11 (1535) transition NN CLAS data : PDG  p  p   M.Dugger First measurements of S 1/2 : Results for A 1/2 obtained in  and  production agree with each other with       PDG:      NN it is difficult to extract S 1/2 in  electroproduction Slow falloff of A 1/2 observed in  production is confirmed by  data Inna Aznauryan

P11(1440) and D13(1520) electrocouplings at Q 2 <0.6 GeV 2. from analysis of CLAS 2  data within the framework of JM06 from analysis of 1  CLAS data combined analysis of 1  CLAS data P11(1440)D13(1520) CLAS 2  data provided compelling evidence for sign flip of P11(1440) A 1/2 electrocoupling. Electrocouplings obtained in analyses of major 1  and 2  channels are in reasonable agreement. Victor Mokeev

Description of CLAS 2  data (cont.) , 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  - angular distributions was achieved in entire kinematics area covered by CLAS data. Victor Mokeev

con’d 3-body processes: Isobar channels included:  + D 0 13 (1520),  + F 0 15 (1685),  - P (1640) isobar channels, observed for the first time in the CLAS data at W>1.65 GeV. Direct 2  production F 0 15(1685) (P ++ 33(1640)) (-)(-) (+)(+) V.Mokeev, V.Burkert, J. Phys. 69, (2007); arXiv [hep-ph] in prep. for PRC

29 Electrocouplings of high lying N*’s. D33(1700) P13(1720) First consistent mapping of Q 2 -dependence for D33(1700), P13(1720) electrocouplings from CLAS data on 2  electroproduction

N(1440)P 11 ’s Puzzle  Most of analyses of N(1440) are based on its BW parameterization, which assumes that the Res is related to an isolated Pole  However, the latest GW PWAs for the elastic  N scattering gives evidence that N(1440) corresponds to a more complicated case of several nearby singularities in the amplitude  Then, the BW description is only an efficient one for N(1440), which could be different in different processes  Some inelastic data indirectly support this point: they give the N(1440) BW mass and width essentially different from the PDG BW values   GW: A 1/2 =  1.9  The analysis of the recent CLAS  + electroproduction data [W = GeV & Q 2 = GeV 2 ] allows to extract helicities for  * p  N(1440)P 11 transition [I.G. Aznauryan et al, arXiv: [nucl-ex]  Since Q 2 -dependences for contributions of different singularities may be different, the set of several singularities might provide the N(1440) BW mass and width depending on the Q 2  Model predictions allow to conclude that N(1440) is a first radial excitation of 3q ground state  This problem can be studied in future measurements with CLAS12 Igor Strakovsky

N(1520)D 13 ’s Puzzle  CLAS12 is favorable for Q 2 evaluation ___ SM08  FA06 [Q 2 = 0] o CLAS [2  ]  CLAS [1  ]  DR [1  ]  Isobar [1  ]  GW: A 3/2 =  2.0  The good agreement for A 3/2 and S 1/2 determination between various resonance extractions gives a more reliable estimate of systematics  Viktor Mokeev, PC 2008 SAID very Preliminary W < 1650 MeV Q 2 = 0.40  0.05 GeV 2 SM08 CLAS40 MAID07 Data   W < 1650 MeV Q 2 = 0.65  0.05 GeV 2 SM08 CLAS65 MAID07 Data   Resonance fit done over a narrow range in W but for all Q 2 a and b are free prmts (no W dependence for the polynomial piece of the structure function)  2 /dp Igor Strakovsky

32 JLAB-MSU model (JM) for 2-  electroproduction 3-body processes: Isobar channels included: All well established N* with  decays and 3/2 + (1720) candidate, seen in CLAS 2  data. Reggeized Born terms & effective FSI&ISI treatment. Extra  contact term. All well established N* with  p decays and 3/2 + (1720) candidate. Diffractive ansatz for non-resonant part &  -line shrinkage in N* region.  -  ++ pp

Craig Roberts

For tomography of DVCS amplitude and GPD quintessence function see Polyakov, PLB659 (2008) 542 QCD string operator Maxim Polyakov

photon is hard For tomography of DVCS amplitude and GPD quintessence function see Polyakov, PLB659 (2008) 542 Maxim Polyakov

Advantage of QCD strings to excite exotic baryons Strong colour field Strong reararngenemt of colour Hard photon removes a quark from N at once The quark returns back New Narrow Nucleon N*(1685) Revealed in eta photoproduction /Kuznetsov, MVP, JETP Lett. 88 (2008) 399/ This is just one of examples of advantage of QCD string probe for studies of baryon excitations. Maxim Polyakov

Search for Exited Baryon States Experimentreactionsbeam pol.target pol.recoil status =================================================================================== G1/G10γp → Nπ, pη, pππ, KΛ/Σ - -Λ,Σcomplete G8 γp → p(ρ,φ,ω) linear--complete G9-FROST γp → Nπ, pη, pππ, KΛ lin./circ.long./trans.Λ,Σ2007 G13 γD → KΛ, KΣcirc./lin.unpol.Λ,Σ 2006/2008 G14-HD γ(HD) → KΛ, KΣ, Nπlin./circ.long./trans.Λ,Σ 2009/2010 C LAS This program will, for the first time, provide complete amplitude information on the KΛ final state (more than 7 independent polarization measurements at each kinematics), and nearly complete information on the Nπ final states.

Andy Sandorfi

45 Resonance Analysis Tools Nucleon resonances are broad and overlapping, careful analyses of angular distributions for differential cross sections and polarization observables are needed. Amplitude & multipole analysis (GWU, SAID) Phenomenological analysis procedures have been developed, e.g. unitary isobar models (UIM), dispersion relations (DR), that separate non-resonant and resonant amplitudes in single channels. Dynamical coupled channel approaches for single and double pion analysis are being developed within the Exited Baryon Analysis Center (EBAC) effort. They are most important in the extraction of transition form factors for higher mass baryon states. Event-based partial wave analyses with maximum-likelihood fit, developed in the search for new mesons states are now being utilized for baryon resonance studies. They fully utilize correlations in the final state (CMU). (Comments by Curtis Meyer).

Coupled Channel Analysis (EBAC)

 Pion-nucleon and 2- pion-nucleon contributions to the non-resonant T matrix.

Summary Transition form factors of the NΔ(1232) measured in large Q 2 range. –no sign of approaching asymptotic QCD limit, needs 12 GeV upgrade –pion dressing of vertex needed to describe form factors Roper P 11 transition form factor determined for the first time. –zero-crossing of magnetic form factor –behaves like a Q 3 radial excitation at short distances Tantalizing hints of new baryon states in KY and Nππ channels –require polarization data to resolve ambiguities in analysis Measurement of multiple polarization observables in Nπ, pη, and KY production needed to resolve ambiguities in baryon resonance analysis. EBAC essential to support the baryon resonance program with coupled channel calculations.

49 Ralf Gothe

The Roper resonance N 1/2 +(1440)P 11 RQM: P 11 (1440) = [56,0+] r P 11 (1440) = Q 3 G P 11 (1440) = (Q 3 ) r (QQ)  The Roper resonance is not a gluonic excitation Q 3 G.  At large distances meson couplings may be important.  At short distances the Roper is best described as a radial excitation of the nucleon. Photocoupling amplitudes carry information on the the internal structure of the state. First observation of a sign change for any nucleon resonance.