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Jefferson Lab, Newport News, VA Philip Cole Idaho State University November 1, 2008. http://conferences.jlab.org/EmNN/ 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

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

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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. N, p, p + -, K, K, p, p 0 using cross sections and polarization observables.

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Electromagnetic Excitation of N*s vv N p p e e vv N NN 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 (

23 Helicity amplitudes of the p P 11 (1440) transition NN 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 C76 025211,2007 First measurements of S 1/2 Inna Aznauryan

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Helicity amplitudes of the p D 13 (1520) transition NN 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

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25 Helicity amplitudes of the p S 11 (1535) transition NN 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: NN 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

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P11(1440) and D13(1520) electrocouplings at Q 2

cond 3-body processes: Isobar channels included: + D 0 13 (1520), + F 0 15 (1685), - P ++ 33 (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, 012019 (2007); arXiv0809.4158[hep-ph] in prep. for PRC

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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

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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 = -50.6 1.9 The analysis of the recent CLAS + electroproduction data [W = 1.15 - 1.69 GeV & Q 2 = 1.7 - 4.5 GeV 2 ] allows to extract helicities for * p N(1440)P 11 transition [I.G. Aznauryan et al, arXiv:0804.0447 [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

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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 = 143.1 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 0 1.6 1.6 1.5 5820 + 1.5 1.2 2.2 3352 W < 1650 MeV Q 2 = 0.65 0.05 GeV 2 SM08 CLAS65 MAID07 Data 0 1.3 1.3 1.1 8271 + 1.1 1.3 1.8 2515 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

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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. - ++ pp

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Craig Roberts

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

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

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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

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Search for Exited Baryon States Experimentreactionsbeam pol.target pol.recoil status =================================================================================== G1/G10p N, p, p, K/ - -,complete G8 p p(,,) linear--complete ----------------------------------------------------------------------------------------------------- G9-FROST p N, p, p, K lin./circ.long./trans.,2007 G13 D K, Kcirc./lin.unpol., 2006/2008 G14-HD (HD) K, K, Nlin./circ.long./trans., 2009/2010 C LAS This program will, for the first time, provide complete amplitude information on the K final state (more than 7 independent polarization measurements at each kinematics), and nearly complete information on the N final states.

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Andy Sandorfi

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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).

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Coupled Channel Analysis (EBAC)

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

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Summary Transition form factors of the N(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 N channels require polarization data to resolve ambiguities in analysis Measurement of multiple polarization observables in N, p, and KY production needed to resolve ambiguities in baryon resonance analysis. EBAC essential to support the baryon resonance program with coupled channel calculations.

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49 Ralf Gothe

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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.