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Brief Summary on the. Jefferson Lab, Newport News, VA. which took place on. October 13-15, 2008. at. Philip Cole Idaho State University November 1, 2008. For more information, see:. http://conferences.jlab.org/EmNN/.

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## Jefferson Lab, Newport News, VA

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**Brief Summary on the**Jefferson Lab, Newport News, VA which took place on October 13-15, 2008 at Philip Cole Idaho State University November 1, 2008. For more information, see: http://conferences.jlab.org/EmNN/ 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 S11(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 potential2) 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, pρ0 using cross sections and polarization observables.**lgp=1/2**gv N lgp=3/2 Electromagnetic Excitation of N*’s e’ p, h, pp γv e N*,△ N’ N A3/2, A1/2, S1/2 Ml+/-, El+/-, Sl+/- DOE Milestone 2012 Measure the electromagnetic excitations of low-lying baryon states (<2 GeV) and their transition form factors over the range Q2 = 0.1 – 7 GeV2 and measure the electro- and photo-production of final states with one and two pseudo-scalar mesons. Volker Burkert**Electromagnetic Probe for Resonance Physics**pN PWA constraint [No theoretical input] Q2 N } · For Q2= 0: · For Q2¹ 0: ( ) 2 Igor Strakovsky**The γNΔ(1232) Quadrupole Transition**Shape at low Q2 pQCD limit pQCD limit SU(6): E1+=S1+=0 Volker Burkert**S11(1535): A near-threshold resonances**S11(1535) in the CQM is a L3Q=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 A1/2(S11) form factor with Q2 suggests a Q3 system rather than a meson-baryon (QQQ-QQ) molecule (no form factor calculations exist for the molecular case). S11(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**within the context of the Whitepaper 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. • N N* Transition Form Factors with CLAS at 11 GeV (Gothe, Mokeev, Burkert, Joo, Stoler, Cole) • Others?**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 GeV2. • How will our proposed N* transition helicity amplitude data in the Q2 region of 5.0 to 10 GeV2 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**lgp=1/2**gv N lgp=3/2 • We anticipate that by studying N* behavior at photon virtualities ranging from 5.0 to 10 GeV2, 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. e’ 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 Q2-behavior of the two components, i.e. a) constituent quark core b) meson-baryon dressing of N-N* photon vertices, which contribute to the A1/2, A3/2, S1/2N-N* transition amplitudes: for the N* states: P33(1232), P11(1440), D13(1520), S11(1535), F15(1685), P13(1720), D33(1700) in the region 5.0 < Q2 < 10 GeV2. γv N*,△ e N A3/2, A1/2, S1/2 Ml+/-, El+/-, Sl+/-**3.How will the data on N-N* transition helicity amplitudes,**obtained at 5.0 < Q2 < 10 GeV2, 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 Q2 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 Q2 be useful in establishing these relations? 4.Is it possible or likely that data on N* electrocouplings at high Q2 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?**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 Q2? 6. What are the prospects of having lattice calculations • which relate the underlying QCD data in N-N* helicity transition amplitudes at Q2 up to 10 GeV2? • 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?**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?**g*p P11 (1440): 3q picture with P11 (1440) as [56,0+]r**Inna Aznauryan All LF RQM describe sign change of A1/2 the amplitudeS1/2 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) 025212 All LF RQM fail to describe the amplitude A1/2 at Q2 < 1 GeV2 Strong evidence in favor of P11 (1440) as a first radial excitation of 3q ground state**P11 (1440): Additional components and contributions**Inna Aznauryan Pion cloud EBAC (preliminary) Julia-Diaz et.al., PR C77(2008)045205 • 30% admixture of • qqqqq components in • the Roper resonance • G(theory) = G(exp) : • Li, Riska, PR C74(2006)015202 Pion cloud contributions and additional qqqqq components in the Roper resonance can improve the description at small Q2**P11 (1440) as a q3G hybrid state**Inna Aznauryan P11 (1440) as a q3G hybrid state is ruled out !!! Supression of S1/2has its origin in the form of the vertex g*q qG; it is practically independent of relativistic effects P11 (1440) as q3G: Li, Burkert,Li, PR D46 (1992) 70**Helicity amplitudes of the g*p P11 (1440) transition**Inna Aznauryan CLAS data : Np Np, Npp, combined gppp0 M.Dugger et al., PR C76 025211,2007 Npp (preliminary) First measurements of S1/2 First measurements of A1/2at Q2 > 0 PDG**Helicity amplitudes of the g*p D13(1520) transition**Inna Aznauryan CLAS data : Np gppp0 ,M. Dugger Np, Npp, combined Npp(preliminary) Old data: Bonn, DESY, NINA First definite results for A 1/2 , A 3/2 in wide range of Q2 First measurements of S1/2 PDG**Helicity amplitudes of the g*p S11 (1535) transition**Inna Aznauryan CLAS data : Np gppp0 M.Dugger Nh it is difficult to extract S1/2inh electroproduction First measurements of S1/2 : Results for A 1/2obtained in p and hproduction agree with each other with bp N = 0.45, b hN = 0.52 PDG: bp N = 0.35-0.55, b hN = 0.45-0.6 PDG Slow falloff of A1/2observed in hproduction is confirmed by p data**P11(1440) and D13(1520) electrocouplings at Q2<0.6 GeV2.**P11(1440) D13(1520) from analysis of 1p CLAS data from analysis of CLAS 2p data within the framework of JM06 combined analysis of 1p/2p CLAS data • CLAS 2p data provided compelling evidence for sign flip of P11(1440) A1/2 electrocoupling. • Electrocouplings obtained in analyses of major 1p and 2p channels are in reasonable agreement. Victor Mokeev**Description of CLAS 2p data (cont.)**s, mcbn Q2=0.65 Gev2 Q2=0.95 Gev2 Q2=1.30 Gev2 Reasonable description of invariant mass and p- angular distributions was achieved in entire kinematics area covered by CLAS data. W, GeV Victor Mokeev**con’d**3-body processes: Isobar channels included: (p-) • p+D013(1520), p+F015(1685), p-P++33(1640) isobar channels, observed for the first time in the CLAS data at W>1.65 GeV. (P++33(1640)) (p+) F015(1685) Direct 2p production V.Mokeev, V.Burkert, J. Phys. 69, 012019 (2007); arXiv0809.4158[hep-ph] in prep. for PRC**Electrocouplings of high lying N*’s.**First consistent mapping of Q2-dependence for D33(1700), P13(1720) electrocouplings D33(1700) D33(1700) from CLAS data on 2p electroproduction P13(1720) P13(1720) 29**N(1440)P11’s Puzzle**·The analysis of the recent CLAS p+ electroproduction data [W = 1.15 - 1.69 GeV & Q2 = 1.7 - 4.5 GeV2] allows to extract helicities for g*pN(1440)P11transition [I.G. Aznauryan et al, arXiv:0804.0447 [nucl-ex] · 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 latestGWPWAs for the elasticpNscattering 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 thePDGBWvalues · · Model predictions allow to conclude that N(1440) is a first radial excitation of 3q ground state · GW: A1/2= -50.61.9 · Since Q2-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 theQ2 ·This problemcan be studied in future measurements withCLAS12 Igor Strakovsky**N(1520)D13’s Puzzle**· GW: A3/2= 143.12.0 c2/dp W < 1650 MeV Q2 = 0.400.05 GeV2 SM08 CLAS40 MAID07 Data p0 1.6 1.6 1.5 5820 p+ 1.5 1.2 2.2 3352 W < 1650 MeV Q2 = 0.650.05 GeV2 SM08 CLAS65 MAID07 Data p0 1.3 1.3 1.1 8271 p+ 1.1 1.3 1.8 2515 SAID very Preliminary SAID very Preliminary ___ SM08 · FA06 [Q2 = 0] o CLAS [2p] D CLAS [1p] D DR [1p] D Isobar [1p] { Resonance fit done over a narrow range in W but for all Q2 a and b are free prmts (no W dependence for the polynomial piece of the structure function) Viktor Mokeev, PC 2008 · The good agreement for A3/2 and S1/2 determination between various resonance extractions gives a more reliable estimate of systematics ·CLAS12 is favorable for Q2 evaluation Igor Strakovsky**JLAB-MSU model (JM) for 2-p electroproduction**Isobar channels included: 3-body processes: p-D++ • All well established N* with pD decays and 3/2+(1720) candidate, seen in CLAS 2p data. • Reggeized Born terms & effective FSI&ISI treatment . • Extra pD contact term. rp • All well established N* with rp decays • and 3/2+(1720) candidate. • Diffractive ansatz for non-resonant part & r-line shrinkage in N* region. 32**QCD string operator**Maxim Polyakov For tomography of DVCS amplitude and GPD quintessence function see Polyakov, PLB659 (2008) 542**Maxim Polyakov**photon is hard For tomography of DVCS amplitude and GPD quintessence function see Polyakov, PLB659 (2008) 542**Advantage of QCD strings to excite exotic baryons**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/ Strong colour field Strong reararngenemt of colour This is just one of examples of advantage of QCD string probe for studies of baryon excitations. Maxim Polyakov**Search for Exited Baryon States**CLAS Experiment reactions beam pol. target pol. recoil status =================================================================================== G1/G10 γp→Nπ, pη, pππ, KΛ/Σ - - Λ,Σ complete G8 γp→p(ρ,φ,ω) linear - - complete ----------------------------------------------------------------------------------------------------- G9-FROST γp→Nπ, pη, pππ, KΛ lin./circ. long./trans. Λ,Σ 2007 G13 γD→KΛ, KΣ circ./lin. unpol. Λ,Σ 2006/2008 G14-HD γ(HD)→KΛ, KΣ, Nπ lin./circ. long./trans. Λ,Σ 2009/2010 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.**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 Q2 range. • no sign of approaching asymptotic QCD limit, needs 12 GeV upgrade • pion dressing of vertex needed to describe form factors • Roper P11 transition form factor determined for the first time. • zero-crossing of magnetic form factor • behaves like a Q3 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.**The Roper resonance N1/2+(1440)P11**RQM:P11(1440) = [56,0+]r P11(1440) = Q3G P11(1440) = (Q3)r(QQ) Photocoupling amplitudes carry information on the the internal structure of the state. • The Roper resonance is not a gluonic excitation Q3G. • At large distances meson couplings may be important. • At short distances the Roper is best described as a radial excitation of the nucleon. First observation of a sign change for any nucleon resonance.

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