Electroexcitation of Nucleon Resonances Volker D Burkert Jefferson

Electroexcitation of Nucleon Resonances Volker D. Burkert Jefferson Lab BARYONS ‘ 02 9 th International Conference on the Structure of Baryons March 3 - 8, 2002 Volker D. Burkert BARYONS’ 02 March 4 -8, 2002 1

Why N*’s are important (Nathan Isgur, N*2000 Conference, Jlab) q Nucleons represent the real world, they must be at the center of any discussion on “why the world is the way it is” Volker D. Burkert BARYONS’ 02 March 4 -8, 2002 2

Why Excitations of the Nucleon? (Nathan Isgur, N*2000 Conference, Jlab) q Nucleons represent the real world, they must be at the center of any discussion on “why the world is the way it is” q Nucleons represent the simplest system where “the non-abelian character of QCD is manifest” Volker D. Burkert BARYONS’ 02 March 4 -8, 2002 3

Why Excitations of the Nucleon? (Nathan Isgur, N*2000 Conference, Jlab) q Nucleons represent the real world, they must be at the center of any discussion on “why the world is the way it is” q Nucleons represent the simplest system where “the non-abelian character of QCD is manifest” q Nucleons/baryons are complex enough to “reveal physics hidden from us in mesons” Gell-Mann & Zweig - Quark Model O. Greenberg - The D++ problem/color Volker D. Burkert BARYONS’ 02 March 4 -8, 2002 4

OUTLINE Ø Why electroproduction? Ø Experimental results q q q Quadrupole deformation in the N-D transition The Roper resonance - N’(1440)1/2+ Eta production and the N*(1535)1/2 SQTM and higher mass states Resonances in multi-pion, and KY* channels? Ø Summary/Outlook Volker D. Burkert BARYONS’ 02 March 4 -8, 2002 5

Why N* Electroproduction? q Light quark baryon spectrum for N* q Internal structure of baryons Np Helicity amplitudes vs Q 2 => Relevant degrees of freedom vs distance scale q Meson production mechanism Volker D. Burkert BARYONS’ 02 March 4 -8, 2002 6

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2 ep. X, E=4 Ge. V missing states CLAS: ep 1. 5 1 0. 5 Volker D. Burkert BARYONS’ 02 1. 0 March 4 -8, 2002 1. 5 8

N-D(1232) Quadrupole Transition SU(6): E 1+=S 1+=0 Volker D. Burkert BARYONS’ 02 March 4 -8, 2002 9

Multipole Ratios REM, RSM - before 2001 Volker D. Burkert BARYONS’ 02 March 4 -8, 2002 10

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Multipole Analysis for g*p ppo Q 2 = 0. 9 Ge. V 2 CLAS |M 1+|2 Re(E 1+M 1+*) |M 1+|2 Re(S 1+M 1+*) L. C. Smith Volker D. Burkert BARYONS’ 02 March 4 -8, 2002 12

Multipole Ratios REM, RSM - before 2001 Volker D. Burkert BARYONS’ 02 March 4 -8, 2002 13

Multipole Ratios REM, RSM - 2002 Volker D. Burkert BARYONS’ 02 March 4 -8, 2002 14

Multipole Ratios REM(Q 2), RSM (Q 2) Bonn(2002) Sato Ernst Volker D. Burkert BARYONS’ 02 March 4 -8, 2002 15

Multipole Ratios REM(Q 2), RSM (Q 2) Bonn(2002) LQCD 1993 Volker D. Burkert BARYONS’ 02 March 4 -8, 2002 16

Multipole Ratios REM(Q 2), RSM (Q 2) Bonn(2002) LQCD 2002? (Moore’s law) Volker D. Burkert BARYONS’ 02 March 4 -8, 2002 17

Polarized Beam Observable ep eppo s response function / CLAS lt’ Beam spin asymmetry Mami/A 2 Joo Botto Kuhn Volker D. Burkert BARYONS’ 02 March 4 -8, 2002 18

The 2 nd Resonance Region The Roper N’(1440)P 11 q In CQM assigned as a N=2 radial excitation of the nucleon q Poor description of properties such as mass, photocouplings, Q 2 evolution Ø Strong gluonic component? Ø Quark core with meson cloud? Ø Ns molecule? Volker D. Burkert BARYONS’ 02 March 4 -8, 2002 19

The 2 nd Resonance Region CLAS ep Volker D. Burkert enp+ Unitary. Isobar fit BARYONS’ 02 March 4 -8, 2002 20

The 2 nd Resonance Region The Roper N’(1440)P 11 q In CQM assigned as a N=2 radial excitation of the nucleon q Poor description of properties such as mass, photocouplings, Q 2 evolution Ø Strong gluonic component? Ø Quark core with meson cloud? Ø Ns molecule? CLAS (preliminary) s(po, p+), Ae(po, p+), unitary isobar fit H. Egiyan Volker D. Burkert BARYONS’ 02 March 4 -8, 2002 21

The 2 nd Resonance Region N*(1535)S 11 Ø CQM assigns state to the [70, 1 -] multiplet Ø Speculation if it is not a |q 3> state but a |KS> molecule Volker D. Burkert BARYONS’ 02 March 4 -8, 2002 22

The 2 nd Resonance Region N*(1535)S 11 Ø CQM assigns state to the [70, 1 -] multiplet Ø Speculation if it is not a |q 3> state but a |KS> molecule Ø Hard e. m. formfactor Ø LQCD indicates clear |q 3> behavior Volker D. Burkert BARYONS’ 02 March 4 -8, 2002 23

The 2 nd Resonance Region N*(1535)S 11 Ø CQM assigns state to the [70, 1 -] multiplet Ø Speculation if it is not a |q 3> state but a |KS> molecule Ø Hard e. m. formfactor Ø LQCD indicates clear |q 3> behavior Ø Strong coupling to ph Volker D. Burkert BARYONS’ 02 March 4 -8, 2002 24

The 2 nd Resonance Region CLAS ep N*(1535)S 11 Ø CQM assigns state to the [70, 1 -] multiplet Ø Speculation if it is not a |q 3> state but a |KS> molecule Ø Hard e. m. formfactor Ø LQCD indicates clear |q 3> behavior Ø Strong coupling to ph Volker D. Burkert BARYONS’ 02 March 4 -8, 2002 eph 25

The 2 nd Resonance Region Photocoupling amplitude A 1/2 N*(1535)S 11 Ø Consistent Q 2 evolution from h production H. Denizli Volker D. Burkert BARYONS’ 02 March 4 -8, 2002 26

The 2 nd Resonance Region Photocoupling amplitude A 1/2 N*(1535)S 11 Ø Consistent Q 2 evolution from h production Giannini and Santopinto Volker D. Burkert BARYONS’ 02 March 4 -8, 2002 27

The 2 nd Resonance Region Photocoupling amplitude A 1/2 N*(1535)S 11 Ø Consistent Q 2 evolution from h production Ø Discrepancy with Np analysis Volker D. Burkert BARYONS’ 02 March 4 -8, 2002 28

The 2 nd Resonance Region Photocoupling amplitude A 1/2 N*(1535)S 11 Ø Consistent Q 2 evolution from h production Ø Discrepancy with Np analysis Ø CLAS ph and Np data consistent Volker D. Burkert CLAS ppo, np+ (preliminary) BARYONS’ 02 March 4 -8, 2002 29

Single Quark Transition Model Ø Transition [56, 0+] -> [70, 1 -] described by 3 amplitudes, e. g. determined from S 11, D 13 Volker D. Burkert BARYONS’ 02 March 4 -8, 2002 30

Single Quark Transition Model Ø Ø Transition [56, 0+] -> [70, 1 -] described by 3 amplitudes, e. g. determined from S 11, D 13 Predicts all other amplitudes in same supermultiplet Volker D. Burkert BARYONS’ 02 March 4 -8, 2002 31

Test of the Single Quark Transition Model Ø Transition [56, 0+] -> [70, 1 -] described by 3 amplitudes, e. g. determined from S 11, D 13 Ø Predicts all other amplitudes in same supermultiplet Ø Tests model in the large Nc limit Ø Good description of Q 2=0 Ø Insufficient Q 2 = 0 data Volker D. Burkert BARYONS’ 02 March 4 -8, 2002 32

Higher mass and “missing states” Ø Higher mass states tend to couple strongly to Npp Volker D. Burkert BARYONS’ 02 March 4 -8, 2002 33

“Missing” Resonances? q Symmetric CQM predicts many more states than observed in elastic p. N scattering analysis |q 3> => predicted to couple to Npp (Dp, Nr), Nw, KY which model is closer to reality? |q 2 q> => fewer excitation degrees of freedom fewer states Klempt, Vijande Volker D. Burkert BARYONS’ 02 March 4 -8, 2002 34

Resonances in g*p pp+p- Total cross section CLAS Genova-Moscow Isobar model fit GNpp PDG GNg AO/SQTM missing resonance strength Volker D. Burkert BARYONS’ 02 March 4 -8, 2002 35

Isobar fit to D 13(1700) and new P 13 Total cross section CLAS Genova-Moscow Isobar model fit GNpp PDG GNg AO/SQTM P 13 D 13(1700) W(Ge. V) Volker D. Burkert BARYONS’ 02 March 4 -8, 2002 36

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Isobar fit - hadronic decays W = 1. 74 Ge. V CLAS P 13 Mp+p D 13(1700) q Mp+p- Data described best by new P 13 M = 1. 72 +/- 0. 02 Ge. V GT = 88 +/- 17 Me. V Dp : 0. 41 +/- 0. 13 Nr : 0. 17 +/- 0. 10 qp- (deg) Volker D. Burkert BARYONS’ 02 March 4 -8, 2002 38

Isobar fit - A new state? W = 1. 74 Ge. V CLAS P 13 Mp+p D 13(1700) q Mp+p- qp- (deg) Data described best by new P 13 M = 1. 72 +/- 0. 02 Ge. V 1650 -1750 100 -200 GT = 88 +/- 17 Me. V Dp : 0. 41 +/- 0. 13 ~0 0. 8 - 0. 9 Nr : 0. 17 +/- 0. 10 q consistent with “missing” P 13 state, but mass low known P 13 F. Klein Volker D. Burkert BARYONS’ 02 March 4 -8, 2002 39

Search for resonances in hyperon production CLAS g*p K+ Y backward hemishere forward hemisphere y r a n i m i l e r p N* N* Niculescu/Feuerbach Volker D. Burkert BARYONS’ 02 March 4 -8, 2002 40

Resonances in g*p pw? above resonance region g s w p p g p -1 CLAS w N* p in resonance region cosqpw +1 F. Klein Volker D. Burkert BARYONS’ 02 March 4 -8, 2002 41

Resonances in Virtual Compton Scattering Hall A - E 93 -50 ep epg Ø First measurement through entire resonance region Ø advantage over mesons, the lack of final state interaction N*(1520) D(1232) Ø strong resonance excitations N*(1650) Fonvieille Todor Volker D. Burkert BARYONS’ 02 March 4 -8, 2002 42

Summary q Accurate results on transition amplitudes for several states give a consistent picture, and allow stringent test of theory Ø D(1232), N*(1535), (Roper) q Searches in various final states suggest excitations of states not seen before Ø pp+p-, pw, K+L , . . q N* electroexcitation has become a major tool in studying the complex regime of strong QCD and confinement Volker D. Burkert BARYONS’ 02 March 4 -8, 2002 43

Outlook q Transition amplitudes for several states under study CLAS, Hall A/C, OOPS q New instrumentation/facilities - BLAST, MAMI upgrade Volker D. Burkert BARYONS’ 02 March 4 -8, 2002 44

Outlook q Transition amplitudes for several states under study CLAS, Hall A/C, OOPS q New instrumentation/facilities - BLAST, MAMI upgrade q The D(1232) is the only resonance so far seen first in electron scattering experiments. Perhaps, this long drought is over soon. The potential is there! Volker D. Burkert BARYONS’ 02 March 4 -8, 2002 45

Outlook q Transition amplitudes for several states under study CLAS, Hall A/C, OOPS q New instrumentation/facilities - BLAST, MAMI upgrade q The D(1232) is the only resonance so far seen first in electron scattering experiments. Perhaps, this long drought is over soon. The potential is there! It is an exciting time to work in this field ! Volker D. Burkert BARYONS’ 02 March 4 -8, 2002 46