1. Single pion electroproduction at CLAS Kijun Park Univ. of South Carolina Kijun Park Univ. of South Carolina 1 st Student Conference 702D 576-6069 Aug. 20, 2008

2. (GeV) lowhigh N π q e.m. probe USC 2008 1 st Student Conference Aug.20, 2008 K. Park Physics Motivation Hadron Structure with e.m. Probes? resolution of probe Allows to address central question: “ What are the relevant degrees-of-freedom at varying distance scale ? ”

3. D 13 (1520) S 11 (1535) P 33 (1232) SU(6)xO(3) Classification of Baryons Missing States? P 11 (1440) Lowest Baryon Supermultiplets SU(6)xO(3) Symmetry Particle Data Group Lowest Baryon Supermultiplets SU(6)xO(3) Symmetry Particle Data Group e e’ γvγv N N’N’ N*,  * A 1/2, A 3/2, S 1/2 π, η, ππ N USC 2008 1 st Student Conference Aug.20, 2008 K. Park

4. D 13 (1520) S 11 (1535) P 33 (1232) SU(6)xO(3) Classification of Baryons Missing States? P 11 (1440) Lowest Baryon Super-multiplets SU(6)xO(3) Symmetry Particle Data Group Lowest Baryon Super-multiplets SU(6)xO(3) Symmetry Particle Data Group * There are questions about underlying degrees-of-freedom of some well known state like P11, S11, D13 * Study of transition from ground state allows make more definite statement about the nature USC 2008 1 st Student Conference Aug.20, 2008 K. Park

5. Kinematic variables Unpol. Cross Section w/ one-photon exchange approx. CLAS and Reaction Channel USC 2008 1 st Student Conference Aug.20, 2008 K. Park

6. UIM and DR fit at low and high Q 2 Number of data points >50,000 Ee = 1.515, 1.645, 5.754GeV ObservableQ2Q2 # of data points 0.40 0.65 3,530 3,818 0.40 0.65 1.7-4.3 2,308 1,716 33,000 0.40 0.65 956 805 0.40 0.65 1.7-4.3 918 812 3,300 0.375 0.750 172 412 Low Q2 : Aznauryan et al., I.PRC 71, 015201, (2005). II.PRC 72, 045201, (2005). Low Q2 : Aznauryan et al., I.PRC 71, 015201, (2005). II.PRC 72, 045201, (2005). high Q2 for Roper : Aznauryan et al., and CLAS collaboration I.arXiv, 0804,0447 (2008). high Q2 for Roper : Aznauryan et al., and CLAS collaboration I.arXiv, 0804,0447 (2008). K.Park et al., (CLAS) Phys. Rev. C 77, 015208, (2008). USC 2008 1 st Student Conference Aug.20, 2008 K. Park

7. γ*NΔ - Transition Form Factors – G M Meson contributions play significant role even at fairly high Q 2. Bare Vertex Dressed Vertex Pion Cloud * USC 2008 1 st Student Conference Aug.20, 2008 K. Park

8. Transition to the 2 nd Resonance Region P 11 (1440) Poorly understood in nrCQMs. 1) lower mass, 2) wrong sign pf photo-coupling Other models: - Light front kinematics (relativity) - Hybrid baryon with gluonic excitation |q 3 G> - Quark core with large meson cloud |q 3 m> - Nucleon-sigma molecule |Nσ> - Dynamically generated resonance S 11 (1535) Hard form factor (slow fall off with Q 2 ) Not a quark resonance, but KΣ dynamical system? D 13 (1520) Change of helicity structure with increasing Q 2 from λ =3/2 dominance to λ =1/2 dominance, predicted in nrCQMs, pQCD. Measure Q 2 dependence of Transition F.F. USC 2008 1 st Student Conference Aug.20, 2008 K. Park

9. P 11 (1440) CQM Comparison at low and high Q 2 K.Park et al., (CLAS) Phys. Rev. C 77, 015208, (2008). I. G. Aznauryan et al., (CLAS)arXiv:080447[nucl-ex] (2008). Submit to PRL  Non-relativistic CQ Models do not reproduce sign of A 1/2 at Q 2 =0, and show no zero- crossing.  Relativistic CQ Models (LC) give correct sign and show zero-crossing but miss strength at Q 2 =0. → go to higher Q 2 to reduce effects of meson contributions. USC 2008 1 st Student Conference Aug.20, 2008 K. Park 1.Weber, PR C41(1990)2783 2.Capstick..PRD51(1995)3598 3.Simula…PL B397 (1997)13 4.Riska..PRC69(2004)035212 5.Aznauryan, PRC76(2007)025212 6.Cano PL B431(1998)270

10. P 11 (1440) Transition FF @ high Q 2, Hybrid State ? Analysis with 1)Unitary Isobar Model (UIM) 2)Fixed-t Dispersion Relations (DR) pπ0pπ0 nπ+nπ+ Nπ, pπ + π - nπ+nπ+ pπ0pπ0 DR UIM Include > 35,000 data points in fits. previous data In a nonrelativistic approximation A 1/2 (Q 2 ) and S 1/2 (Q 2 ) behave like the γ*NΔ(1232) amplitudes. Suppression of S 1/2 has its origin in the form of vertex γq→qG. It is practically independent of relativistic effects Z.P. Li, V. Burkert, Zh. Li, PRD46 (1992) 70  G q3q3 USC 2008 1 st Student Conference Aug.20, 2008 K. Park

11. S 11 (1535) in pη and Nπ pπ0pπ0 nπ+nπ+ pπ0pπ0 nπ+nπ+ pηpη New CLAS results preliminary pηpη CLAS 2007 CLAS 2002 previous results CQM A 1/2 from pη and Nπ are consistent PDG 2006 PDG (2006): S 11 → πN (35-55)% → ηN (45-60)% H. Denizli et al., (CLAS) Phys. Rev. C 76, 015204, (2007). USC 2008 1 st Student Conference Aug.20, 2008 K. Park

12. Transition γ*p→D 13 (1520) A 1/2 A 3/2 Q 2, GeV 2 Previous pπ 0 based data preliminary pπ0pπ0 nπ+nπ+ Nπ, pπ + π - nπ+nπ+ pπ0pπ0 PDG nrCQM: USC 2008 1 st Student Conference Aug.20, 2008 K. Park

13. Helicity Asymmetry for γ*p→D 13 (1520) CQMs and pQCD A hel → +1 at Q 2 →∞ CQMs and pQCD A hel → +1 at Q 2 →∞ Helicity structure of transition changes rapidly with Q 2 from helicity 3/2 (A hel = -1) to helicity 1/2 (A hel = +1) dominance! preliminary pπ0pπ0 pπ0pπ0 nπ+nπ+ nπ+nπ+ pπ+π-pπ+π- pπ+π-pπ+π- nπ+nπ+ nπ+nπ+ pπ0pπ0 pπ0pπ0 USC 2008 1 st Student Conference Aug.20, 2008 K. Park

14. Axial Form Factor near the pion threshold region USC 2008 1 st Student Conference Aug.20, 2008 K. Park

15. Perspective of soft pion in terms of Q2 at threshold Low-Energy Theorem (LET) for Q 2 =0 Restriction to the charged pion χral symmetry + current algebra for electroproduction Re-derived LETs Current algebra + PCAC χral perturbation theory pQCD factorization methods 1954 1960s 1970s Kroll-Ruderman Nambu, Laurie, Schrauner Vainshtein, Zakharov 1990s Scherer, Koch Brodsky, Lepage, Efremov, Radyunshkin, Pobylitsa, Polyakov, Strikman, et al USC 2008 1 st Student Conference Aug.20, 2008 K. Park Light Corn Sum Rule Reproduce LET for Q 2 ~ 1GeV 2 Reproduce pQCD for Q 2 →∞ 2007 V. Braun Extended for near pion threshold regions

16. Differential Cross section Only S-wave contribution USC 2008 1 st Student Conference Aug.20, 2008 K. Park

17. Cross section ( φ* ) φ* – dependent cross section in term of W, Q 2, cosθ* Various physics models Differential Cross Sections Blue data : CRS with New Acc. From GENEV Red data : CRS with Old Acc. From AAO Preliminary USC 2008 1 st Student Conference Aug.20, 2008 K. Park

18. Structure Function Sensitive ! Preliminary USC 2008 1 st Student Conference Aug.20, 2008 K. Park

19. MAID03 SLee04 Lines : MAID07 Bold : Real Thin : Imaginary Q 2 dependence of the Normalized E 0+ Multipole by dipole Preliminary RC corr. base on MAID03 RC corr. base on S-Lee04 Color index USC 2008 1 st Student Conference Aug.20, 2008 K. Park

20. Deep Inelastic Scattering Region USC 2008 1 st Student Conference Aug.20, 2008 K. Park

21. Physics Motivation t-channel scaling behavior at large angle Non-pertubative transition between pion and baryon in backward angle Generalized scaling law appears at above resonance region and large angle( θ=90 o ) Investigation of Transition Distribution Amplitude u-channel scaling at backward angle Generalized scaling law appears at large angle related to isospin (3/2 or 1/2) L.Y. Zhu, PRL 91, 022003 (2003) J.P. Lansberg, B. Pire, PRD75,074004 (2007) J. Phys. G : Nucl. Phys. Vol4 No 11, (1978) USC 2008 1 st Student Conference Aug.20, 2008 K. Park

22. Analysis Steps for 9 xbj bins CRS with low t ACC CRS with high t ACC Preliminary USC 2008 1 st Student Conference Aug.20, 2008 K. Park

23. Analysis Steps Fit function Extracting power factor : B Preliminary Slope of fit : B Slope parameter vs. -t Horizontal red line = -8 USC 2008 1 st Student Conference Aug.20, 2008 K. Park

24.  Polarization data to improve resonance separation  New data on Q 2 dependence of higher mass states  An extensive program is underway with polarized photon beams and polarized target to search for new baryon states (CLAS)  Large effort underway at EBAC to develop the coupled channel analysis of these and other data  Proposal for a transition form factor program at high Q 2 for the Jlab 12 GeV upgrade with CLAS12  Full LQCD simulations with high precision planned for near future  Extract new cross sections on above pion threshold region  Extract very preliminary E 0+ /G D for nπ+ channel  We measured the differential cross section with extended – t region  Systematic uncertainties has been studied at low – t region and ongoing at high – t region.  We looked at the backward angle pion electroproduction in the u -channel by extracting the cross section ( dσ/du )  Polarization data to improve resonance separation  New data on Q 2 dependence of higher mass states  An extensive program is underway with polarized photon beams and polarized target to search for new baryon states (CLAS)  Large effort underway at EBAC to develop the coupled channel analysis of these and other data  Proposal for a transition form factor program at high Q 2 for the Jlab 12 GeV upgrade with CLAS12  Full LQCD simulations with high precision planned for near future  Extract new cross sections on above pion threshold region  Extract very preliminary E 0+ /G D for nπ+ channel  We measured the differential cross section with extended – t region  Systematic uncertainties has been studied at low – t region and ongoing at high – t region.  We looked at the backward angle pion electroproduction in the u -channel by extracting the cross section ( dσ/du ) USC 2008 1 st Student Conference Aug.20, 2008 K. Park