Ralf W. Gothe PHYS 745G 1  Motivation: Why Nucleon Transition Form Factors?  Consistency: N  N Roper, and other N N* Transitions  Outlook: Experiment and Theory Ralf W. Gothe Seminar PHYS 745G Columbia, May 29 Hadron Spectroscopy at CLAS: The Evolution of Strong Degrees of Freedom

Ralf W. Gothe PHYS 745G 2 Physics Goals Models Quarks and Gluons as Quasiparticles ChPT Nucleon and Mesons pQCD q, g, qq 1.0 fm <  Determine the electrocouplings of prominent excited nucleon states (N *, Δ * ) in the unexplored Q 2 range of GeV 2 that will allow us to:  Study the structure of the nucleon spectrum in the domain where dressed quarks are the major active degree of freedom.  Explore the formation of excited nucleon states in interactions of dressed quarks and their emergence from QCD. vv N  p   p  ? ! ! ? ? ? ! !

Ralf W. Gothe PHYS 745G 3 What do we really know?

Ralf W. Gothe PHYS 745G 4 Quark Model Classification of N*  (1232) D 13 (1520) S 11 (1535) Roper P 11 (1440) + q³g + q³qq + N-Meson + …

Ralf W. Gothe PHYS 745G 5 N and  Excited States …  Orbital excitations (two distinct kinds)  Radial excitations (also two kinds)

Ralf W. Gothe PHYS 745G 6 “Missing” Resonances? fewer degrees-of-freedom open question: mechanism for q 2 formation? Problem: symmetric CQM predicts many more states than observed (in  N scattering) Possible solutions: 1. di-quark model 2. not all states have been found possible reason: decouple from  N-channel model calculations: missing states couple to N , N , N , KY 3. coupled channel dynamics all baryonic and mesonic excitations beyond the groundstate octets and decuplet are generated by coupled channel dynamics (not only  (1405),  (1520), S 11 (1535) or f 0 (980)) old but always young new

Ralf W. Gothe PHYS 745G 7 E max ~ 6 GeV I max ~ 200  A Duty Factor~ 100%  E /E~ Beam P~ 85% E  (tagged) ~ GeV CLAS The 6 GeV CW Electron Accelerator at JLab

Ralf W. Gothe PHYS 745G 8 CLAS at JLab

Ralf W. Gothe PHYS 745G 9 CLAS for Inclusive ep e’X at 4 GeV CLAS  Resonances cannot be uniquely separated in inclusive scattering

Ralf W. Gothe PHYS 745G 10 CLAS for Exclusive ep e’pX at 4 GeV missing states CLAS

Ralf W. Gothe PHYS 745G 11 SU(6): E 1+ =S 1+ =0 N  (1232) Transition Form Factors

Ralf W. Gothe PHYS 745G 12 Multipole Ratios R EM, R SM before 1999 Sign? Q 2 dependence?  Data could not determine sign or Q 2 dependence

Ralf W. Gothe PHYS 745G 13  Lattice QCD indicates a small oblate deformation of the  (1232) and that the pion cloud makes E 1+ /M 1+ more negative at small Q 2.  Data at low Q 2 needed to study effects of the pion cloud. Need data at low Q 2 N  (1232) Transition Form Factors

Ralf W. Gothe PHYS 745G 14 C. Alexandrou et al., PRL, 94, (2005) R EM (%) R SM (%)  Quenched LQCD describes R EM within error bars, but shows discrepancies with R SM at low Q 2. Pion cloud effects? Low Q 2 Mutipole Ratios for R EM, R SM Need data at low Q 2

Ralf W. Gothe PHYS 745G 15 Low Q 2 Mutipole Ratios for R EM, R SM C. Alexandrou et al., PRL, 94, (2005) preliminary  Quenched LQCD describes R EM within error bars, but shows discrepancies with R SM at low Q 2. Pion cloud effects?  Significant discrepancy between CLAS and Bates/MAMI results for R SM. C. Smith

Ralf W. Gothe PHYS 745G 16  Data at even lower Q 2 are needed to investigate the pion cloud further.  Data at high Q 2 are needed to study the transition to pQCD. Preliminary Multipole Ratios R EM, R SM preliminary Need data at low Q 2

Ralf W. Gothe PHYS 745G 17 quark mass (GeV) Quark mass extrapolated to the chiral limit, where q is the momentum variable of the tree-level quark propagator using the Asqtad action.  … resolution low high q e.m. probe LQCD (Bowman et al.) Hadron Structure with Electromagnetic Probes N,N *,  * … 3q-core+MB-cloud 3q-core pQCD LQCD, DSE and …

Ralf W. Gothe PHYS 745G 18 M. Polyakov

Ralf W. Gothe PHYS 745G 19 S 11 Q 3 A 1/2 F 15 Q 5 A 3/2 P 11 Q 3 A 1/2 D 13 Q 5 A 3/2 F 15 Q 3 A 1/2 D 13 Q 3 A 1/2 Constituent Counting Rule  A 1/2  1/Q 3  A 3/2  1/Q 5  G M  1/Q 4 * Quark mass extrapolated to the chiral limit, where q is the momentum variable of the tree-level quark propagator using the Asqtad action. quark mass (GeV ) Bowman et al. (LQCD)

Ralf W. Gothe PHYS 745G 20 N →  Multipole Ratios R EM, R SM  New trend towards pQCD behavior does not show up.  CLAS12 can measure R EM and R SM up to Q² ~ 12 GeV².  R EM +1 M. Ungaro  G M 1/Q 4 * G D = 1 (1+Q 2 /0.71) 2

Ralf W. Gothe PHYS 745G 21 N →  Multipole Ratios R EM, R SM A. Villano very preliminary e p e'p  0 … but the trend that R SM becomes constant in the limit of Q 2 → ∞ seems to show up in the latest MAID 2007 analysis of the high Q 2 data.

Ralf W. Gothe PHYS 745G 22 Integrated Target and Beam-Target Asymmetries A. Biselli The asymmetries are integrated over  * and  * in the Q 2 range from to GeV 2 and will further reduce the model dependence of the extracted resonance parameters. e p e'p  0

Ralf W. Gothe PHYS 745G 23 Progress in Experiment and Phenomenology Dressed quarks (I. Aznauryan, M. Giannini and E. Santopinto, B. Julia-Diaz et al.) Meson-baryon cloud (EBAC) N  NN NN p0p0  (1232)P 33 N(1440)P 11 N(1520)D 13 Recent experimental and phenomenological efforts show that meson- baryon contributions to resonance formations drop faster with Q 2 than contributions from dressed quarks. A 1/2

Ralf W. Gothe PHYS 745G 24 Resonance Electrocouplings in Lattice QCD LQCD calculations of the  (1232)P 33 and N(1440)P 11 transitions have been carried out with large  -masses. By the time of the upgrade LQCD calculations of N* electrocouplings will be extended to Q 2 = 10 GeV 2 near the physical  -mass as part of the commitment of the JLab LQCD and EBAC groups in support of this proposal.  (1232)P 33 N(1440)P 11 see White Paper Sec. II and VIII Huey-Wen Lin

Ralf W. Gothe PHYS 745G 25 LQCD & Light Cone Sum Rule (LCSR) Approach LQCD is used to determine the moments of N* distribution amplitudes (DA) and the N* electrocouplings are determined from the respective DAs within the LCSR framework. Calculations of N(1535)S 11 electrocouplings at Q 2 up to 12 GeV 2 are already available and shown by shadowed bands on the plot. By the time of the upgrade electrocouplings of others N*s will be evaluated. These studies are part of the commitment of the Univ. of Regensburg group in support of this proposal. see White Paper Sec. V N(1535)S 11 CLAS Hall C

Ralf W. Gothe PHYS 745G 26 Dynamical Mass of Light Dressed Quarks DSE and LQCD predict the dynamical generation of the momentum dependent dressed quark mass that comes from the gluon dressing of the current quark propagator. These dynamical contributions account for more than 98% of the dressed light quark mass. The data on N* electrocouplings at 5<Q 2 <12 GeV 2 will allow us to chart the momentum evolution of dressed quark mass, and in particular, to explore the transition from dressed to almost bare current quarks as shown above. per dressed quark Q 2 = 12 GeV 2 = (p times number of quarks) 2 = 12 GeV 2 p = 1.15 GeV DSE: lines and LQCD: triangles

Ralf W. Gothe PHYS 745G 27 Dyson-Schwinger Equation (DSE) Approach DSE provides an avenue to relate N* electrocouplings at high Q 2 to QCD and to test the theory’s capability to describe N* formations based on QCD. DSE approaches provide a link between dressed quark propagators, form factors, scattering amplitudes, and QCD. N* electrocouplings can be determined by applying Bethe-Salpeter / Fadeev equations to 3 dressed quarks while the properties and interactions are derived from QCD. By the time of the upgrade DSE electrocouplings of several excited nucleon states will be available as part of the commitment of the Argonne NL and the University of Washington. see White Paper Sec. III

Ralf W. Gothe PHYS 745G 28 Constituent Quark Models (CQM) Pion Cloud (EBAC) |q 3 +qq  (Li, Riska) 3q Relativistic CQM are currently the only available tool to study the electrocouplings for the majority of excited proton states. This activity represent part of the commitment of the Yerevan Physics Institute, the University of Genova, INFN-Genova, and the Beijing IHEP groups to refine the model further, e.g., by including qq components. see White Paper Sec. VI LC CQM PDG value NN N , N  combined analysis N(1440)P 11 :

Ralf W. Gothe PHYS 745G 29 Phenomenological Analyses  Unitary Isobar Model (UIM) approach in single pseudoscalar meson production  Fixed-t Dispersion Relations (DR)  Isobar Model for Nππ final state (JM)  Coupled-Channel Approach (EBAC) see White Paper Sec. VIII see White Paper Sec. VII

Ralf W. Gothe PHYS 745G 30 Unitary Isobar Model (UIM) Nonresonant amplitudes: gauge invariant Born terms consisting of t-channel exchanges and s- / u-channel nucleon terms, reggeized at high W.  N rescattering processes in the final state are taken into account in a K-matrix approximation. Fixed-t Dispersion Relations (DR) Relates the real and the imaginary parts of the six invariant amplitudes in a model-independent way. The imaginary parts are dominated by resonance contributions. Phenomenological Analyses in Single Meson Production see White Paper Sec. VII

Ralf W. Gothe PHYS 745G 31 Legendre Moments of Unpolarized Structure Functions Q 2 =2.05GeV 2 Two conceptually different approaches DR and UIM are consistent. CLAS data provide rigid constraints for checking validity of the approaches. K. Park et al. (CLAS), Phys. Rev. C77, (2008) I. Aznauryan DR fit w/o P 11 I. Aznauryan DR fit I. Aznauryan UIM fit

Ralf W. Gothe PHYS 745G 32 Energy-Dependence of  + Multipoles for P 11, S 11 imaginary partreal part Q 2 = 0 GeV 2 The study of some baryon resonances becomes easier at higher Q 2. Q 2 = 2.05 GeV 2 preliminary

Ralf W. Gothe PHYS 745G 33 BES/BEPC, Phys. Rev. Lett. 97 (2006) Bing-Song Zou and    ±     ±        -     ±   invariant mass / MC phase space

Ralf W. Gothe PHYS 745G 34 Nucleon Resonances in N  and N  Electroproduction p(e,e')X p(e,e'p)   p(e,e'  + )n p(e,e'p  + )  -   channel is sensitive to N*s heavier than 1.4 GeV  Provides information that is complementary to the N  channel  Many higher-lying N*s decay preferentially into N  final states Q 2 < 4.0 GeV 2 W in GeV

Ralf W. Gothe PHYS 745G 35    (1232)P 33, N(1520)D 13,  (1600)P 33, N(1680)F 15 JM Model Analysis of the p  +  - Electroproduction see White Paper Sec. VII

Ralf W. Gothe PHYS 745G 36 JM Mechanisms as Determined by the CLAS 2  Data Each production mechanism contributes to all nine single differential cross sections in a unique way. Hence a successful description of all nine observables allows us to check and to establish the dynamics of all essential contributing mechanisms. Full JM calculation  -   ++  + N(1520) D 13  + N(1685) F 15 pp 2  direct

Ralf W. Gothe PHYS 745G 37 Separation of Resonant/Nonresonant Contributions in 2  Cross Sections Due to the marked differences in the contributions of the resonant and nonresonant parts to the cross sections, the nine observables allow us to neatly disentangle these competing processes. resonant part nonresonant part

Ralf W. Gothe PHYS 745G 38 Electrocouplings of N(1440)P 11 from CLAS Data N  (UIM, DR) PDG estimation N , N  combined analysis N  (JM) The good agreement on extracting the N* electrocouplings between the two exclusive channels (1  /2  ) – having fundamentally different mechanisms for the nonresonant background – provides evidence for the reliable extraction of N* electrocouplings.

Ralf W. Gothe PHYS 745G 39 Comparison of MAID 08 and JLab analysis A 1/2 S 1/2 Roper Electro-Coupling Amplitudes A 1/2, S 1/2 L. Tiator MAID 07 and new Maid analysis with Park data MAID 08

Ralf W. Gothe PHYS 745G 40 N(1520)D 13 Electrocoupling Amplitudes A 3/2, S 1/2 I. Starkovski

Ralf W. Gothe PHYS 745G 41 Electrocouplings of N(1520)D 13 from the CLAS 1  /2  data world data GeV -1/2 N  (UIM, DR) PDG estimation N , N  combined analysis N  (JM) A hel = A 1/2 2 – A 3/2 2 A 1/2 2 + A 3/2 2 A 1/2 A 3/2 L. Tiator

Ralf W. Gothe PHYS 745G 42 N(1700)D 33 N(1720)P 13 Combined 1  -2  JM Analysis of CLAS Data  PDG at Q 2 =0  Previous world data  2  analysis  1  -2  combined at //// Q 2 =0.65 GeV 2  Many more examples: //// P 11 (1440), D 13 (1520), S 31 (1650), //// S 11 (1650), F 15 (1685), D 13 (1700), //// … preliminary

Ralf W. Gothe PHYS 745G 43  CLAS N  world N  world Q 2 =0  (1700)D 33 N(1720)P 13 Higher Lying Resonances form the 2  JM Analysis of CLAS Data preliminary The A 1/2 electrocoupling of P 13 (1720) decreases rapidly with Q 2. At Q 2 >0.9 GeV 2 |A 3/2 |>|A 1/2 |. Will we able to access the Q 2 region where the A 1/2 amplitude of P 13 (1720) dominates?

Ralf W. Gothe PHYS 745G 44 High lying resonance in N  CLAS data analysis D 33 (1700)P 13 (1720) N  CLAS N  world N  world Q 2 =0  The Analysis of the CLAS N  data provides for the first time information on electrocouplings of N*s that dominantly decay into the N  final states:  The A 1/2 electrocoupling of P 13 (1720) decreases rapidly with Q 2. At Q 2 >0.9 GeV 2 |A 3/2 |>|A 1/2 |. Will we able to access the Q 2 region where the A 1/2 amplitude of P 13 (1720) dominates?

Ralf W. Gothe PHYS 745G 45 Combined 1  -2  Analysis of CLAS Data  PDG at Q 2 =0  2  analysis  1  -2  combined at Q 2 =0.65 GeV 2  Previous world data preliminary

Ralf W. Gothe PHYS 745G 46 CLAS12 Detector Base Equipment

Ralf W. Gothe PHYS 745G 47 Inclusive Structure Function in the Resonance Region P. Stoler, PRPLCM 226, 3 (1993)

Ralf W. Gothe PHYS 745G 48 CLAS 12 Kinematic Coverage and Counting Rates Genova-EG SI-DIS (e',  + ) detected (e', p) detected (e ’,  + ) detected (E,Q 2 )(5.75 GeV, 3 GeV 2 )(11 GeV, 3 GeV 2 )(11 GeV, 12 GeV 2 ) N+N    10 4 NpNp   10 4 NpNp   days L=10 35 cm -2 sec -1, W=1535 GeV,  W= GeV,  Q 2 = 0.5 GeV 2

Ralf W. Gothe PHYS 745G 49 Angular Acceptance of CLAS12  + Acceptance for cos  = 0.01 Full kinematical coverage in W, Q 2, , and 

Ralf W. Gothe PHYS 745G < W < 2 GeV 60 MeV 1.5 < W < 2 GeV 10 MeV W < 2 GeV 33 22 W and Missing Mass Resolutions with CLAS12 W calculated from electron scattering exclusive p  +   final state ep  e'p'  + X Final state selection by Missing Mass M X 2 (GeV 2 ) FWHM

Ralf W. Gothe PHYS 745G 51 Kinematic Coverage of CLAS12 60 days L= cm -2 sec -1,  W = GeV,  Q 2 = 0.5 GeV 2 Genova-EG (e ’, p     ) detected W GeV Q 2 GeV 2 2  limit >1  limit > 2  limit >1  limit > 1  limit >

Ralf W. Gothe PHYS 745G 52 Summary  We will measure and determine the electrocouplings A 1/2, A 3/2, S 1/2 as a function of Q 2 for prominent nucleon and Δ states,  see our Proposal  Comparing our results with LQCD, DSE, LCSR, and rCQM will gain insight into  the strong interaction of dressed quarks and their confinement in baryons,  the dependence of the light quark mass on momentum transfer, thereby shedding light on chiral-symmetry breaking, and  the emergence of bare quark dressing and dressed quark interactions from QCD.  This unique opportunity to understand origin of 98% of nucleon mass is also an experimental and theoretical challenge. A wide international collaboration is needed for the:  theoretical interpretation on N* electrocouplings, see our White Paper and  development of reaction models that will account for hard quark/parton contributions at high Q 2.  Any constructive criticism or direct participation is very welcomed, please contact:  Viktor Mokeev or Ralf Gothe

Ralf W. Gothe PHYS 745G 53 Conclusion: Do Exclusive Electron Scattering Q 2 = 2.05 GeV 2 D 13 (1520)... to Learn QCD!

Ralf W. Gothe PHYS 745G 54 Supplement

Ralf W. Gothe PHYS 745G 55 Nucleon Resonance Studies with CLAS12 D. Arndt 4, H. Avakian 6, I. Aznauryan 11, A. Biselli 3, W.J. Briscoe 4, V. Burkert 6, V.V. Chesnokov 7, P.L. Cole 5, D.S. Dale 5, C. Djalali 10, L. Elouadrhiri 6, G.V. Fedotov 7, T.A. Forest 5, E.N. Golovach 7, R.W. Gothe* 10, Y. Ilieva 10, B.S. Ishkhanov 7, E.L. Isupov 7, K. Joo 9, T.-S.H. Lee 1,2, V. Mokeev* 6, M. Paris 4, K. Park 10, N.V. Shvedunov 7, G. Stancari 5, M. Stancari 5, S. Stepanyan 6, P. Stoler 8, I. Strakovsky 4, S. Strauch 10, D. Tedeschi 10, M. Ungaro 9, R. Workman 4, and the CLAS Collaboration JLab PAC 34, January 26-30, 2009 Argonne National Laboratory (IL,USA) 1, Excited Baryon Analysis Center (VA,USA) 2, Fairfield University (CT, USA) 3, George Washington University (DC, USA) 4, Idaho State University (ID, USA) 5, Jefferson Lab (VA, USA) 6, Moscow State University (Russia) 7, Rensselaer Polytechnic Institute (NY, USA) 8, University of Connecticut (CT, USA) 9, University of South Carolina (SC, USA) 10, and Yerevan Physics Institute (Armenia) 11 Spokesperson Contact Person*

Ralf W. Gothe PHYS 745G 56 Theory Support Group V.M. Braun 8, I. Cloët 9, R. Edwards 5, M.M. Giannini 4,7, B. Julia-Diaz 2, H. Kamano 2, T.-S.H. Lee 1,2, A. Lenz 8, H.W. Lin 5, A. Matsuyama 2, M.V. Polyakov 6, C.D. Roberts 1, E. Santopinto 4,7, T. Sato 2, G. Schierholz 8, N. Suzuki 2, Q. Zhao 3, and B.-S. Zou 3 JLab PAC 34, January 26-30, 2009 Argonne National Laboratory (IL,USA) 1, Excited Baryon Analysis Center (VA,USA) 2, Institute of High Energy Physics (China) 3, Istituto Nazionale di Fisica Nucleare (Italy) 4, Jefferson Lab (VA, USA) 5, Ruhr University of Bochum (Germany) 6, University of Genova (Italy) 7, University of Regensburg (Germany) 8, and University of Washington (WA, USA) 9

Ralf W. Gothe PHYS 745G 57 Physics Goals  Measure differential cross sections and polarization observables in single and double pseudoscalar meson production:  + n  0 p,  p and  +   p over the full polar and azimuthal angle range.  Determine electrocouplings of prominent excited nucleon states (N *, Δ * ) in the fully unexplored Q 2 range of 5-12 GeV 2 and extend considerably the data base on fundamental form factors of nucleon states, which is needed to explore the confinement in the baryon sector.  These data for the first time will allow us to:  Study the structure of the nucleon spectrum in the domain where dressed quarks are the major active degree of freedom.  Explore the formation of excited nucleon states in interactions of dressed quarks and their emergence from QCD. “ultimate goal” “address more sharply”

Ralf W. Gothe PHYS 745G 58 Projected A 1/2 Helicity Amplitudes CLAS published CLAS preliminary CLAS12 projected

Ralf W. Gothe PHYS 745G 59 Angular Acceptance of CLAS12  + Acceptance for cos  = 0.01 Full kinematical coverage in W, Q 2, , and 

Ralf W. Gothe PHYS 745G 60 preliminary S 11 (1535) Electro-Coupling Amplitudes A 1/2, S 1/2  electro-production (UIM, DR) PDG estimation  production (SQTM S 11, D 13 analysis) K. Park (Data) I. Aznauryan (UIM)   production (UIM, DR) nr |q 3  LF |q 3  nr |q 3  LF |q 3  nr |q 3 

Ralf W. Gothe PHYS 745G 61 preliminary D 13 (1520) Helicity Asymmetry A hel = A 1/2 2 – A 3/2 2 A 1/2 2 + A 3/2 2 A 1/2 A 3/2

Ralf W. Gothe PHYS 745G 62 direct 2   production Full calculations  p   -  ++  p   +  0  p   p  p   -  ++ (1600)  p   + F 0 15 (1685)  p   + D 13 (1520)  The combined fit of nine single differential cross sections allowed to establish all significant mechanisms. Isobar Model JM05 Contributing Mechanisms to     p → p  +  -

Ralf W. Gothe PHYS 745G 63 Separation of Resonant/Nonresonant Contributions in 2  Cross Sections full cross sections resonant part non-resonant part The reliable resonant / non- resonant cross section separation allows to isolate the N* contribution and demonstrates the degree of model independence.

Ralf W. Gothe PHYS 745G 64 Helicity Asymmetry in 2  Production CLAS parity conservation Calculations: Mokeev (dashed) Fix (solid) S. Strauch

Ralf W. Gothe PHYS 745G 65 Helicity Asymmetry in 2  Production  Sequential Decay of the D 13 (1520) resonance via   … or higher lying resonances CLASS. Strauch