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

(GeV) lowhigh N π q e.m. probe USC 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 ? ”

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 st Student Conference Aug.20, 2008 K. Park

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 st Student Conference Aug.20, 2008 K. Park

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

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 ,530 3, ,308 1,716 33, , Low Q2 : Aznauryan et al., I.PRC 71, , (2005). II.PRC 72, , (2005). Low Q2 : Aznauryan et al., I.PRC 71, , (2005). II.PRC 72, , (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, , (2008). USC st Student Conference Aug.20, 2008 K. Park

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 st Student Conference Aug.20, 2008 K. Park

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 st Student Conference Aug.20, 2008 K. Park

P 11 (1440) CQM Comparison at low and high Q 2 K.Park et al., (CLAS) Phys. Rev. C 77, , (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 st Student Conference Aug.20, 2008 K. Park 1.Weber, PR C41(1990) Capstick..PRD51(1995) Simula…PL B397 (1997)13 4.Riska..PRC69(2004) Aznauryan, PRC76(2007) Cano PL B431(1998)270

P 11 (1440) Transition 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 st Student Conference Aug.20, 2008 K. Park

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, , (2007). USC st Student Conference Aug.20, 2008 K. Park

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 st Student Conference Aug.20, 2008 K. Park

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 st Student Conference Aug.20, 2008 K. Park

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

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 s 1970s Kroll-Ruderman Nambu, Laurie, Schrauner Vainshtein, Zakharov 1990s Scherer, Koch Brodsky, Lepage, Efremov, Radyunshkin, Pobylitsa, Polyakov, Strikman, et al USC 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

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

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 st Student Conference Aug.20, 2008 K. Park

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

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 st Student Conference Aug.20, 2008 K. Park

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

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, (2003) J.P. Lansberg, B. Pire, PRD75, (2007) J. Phys. G : Nucl. Phys. Vol4 No 11, (1978) USC st Student Conference Aug.20, 2008 K. Park

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

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

 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 st Student Conference Aug.20, 2008 K. Park