Single Pion Electroproduction Kijun Park Oct. 16, 2008 Hall-B Thomas Jefferson National Accelerator Facility

(GeV) lowhigh N π q e.m. probe Hall-B TJNAF 2008 Interview-Seminar Oct.16, 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 ? ” Allows to address central question: “ What are the relevant degrees-of-freedom at varying distance scale ? ” Dyson Schwinger et al.

Hall-B TJNAF 2008 Interview-Seminar Oct.16, 2008 K. Park Transition Form Factors Axial Form Factors pion threshold Deep Inelastic Scattering Region Charged double pions photoproduction OutlookOutlook Each of them linked to interesting physics

Transition Form Factors Hall-B TJNAF 2008 Interview-Seminar Oct.16, 2008 K. Park

D 13 (1520) S 11 (1535) P 33 (1232) SU(6)xO(3) Classification of Baryons in CQM 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 Hall-B TJNAF 2008 Interview-Seminar Oct.16, 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 Hall-B TJNAF 2008 Interview-Seminar Oct.16, 2008 K. Park

Kinematic variables Unpol. Cross Section w/ one-photon exchange approx. CLAS and Reaction Channel Hall-B TJNAF 2008 Interview-Seminar Oct.16, 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). Hall-B TJNAF 2008 Interview-Seminar Oct.16, 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 But no systematic study has been done Measure Q 2 dependence of Transition F.F. Hall-B TJNAF 2008 Interview-Seminar Oct.16, 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. 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 Hall-B TJNAF 2008 Interview-Seminar Oct.16, 2008 K. Park

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 Hall-B TJNAF 2008 Interview-Seminar Oct.16, 2008 K. Park

S 11 (1535) in pη and Nπ pπ0pπ0 nπ+nπ+ pπ0pπ0 nπ+nπ+ pηpη 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). Hall-B TJNAF 2008 Interview-Seminar Oct.16, 2008 K. Park pπ0pπ0 pπ0pπ0 nπ+nπ+ nπ+nπ+ nπ+nπ+ nπ+nπ+ New CLAS results In nπ+, the S 0+ amplitude interferes with the strong M 1- allowing access to the longitudinal coupling Sign of S 1/2 not consistent with CQM, but agrees with dynamically generated resonance prediction.

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: Hall-B TJNAF 2008 Interview-Seminar Oct.16, 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 Hall-B TJNAF 2008 Interview-Seminar Oct.16, 2008 K. Park

P 11 (1440) S 11 (1535) D 13 (1520)  Rapid switch of helicity structure from A 3/2 dominance to A 1/2 dominance at Q 2 > 0.6GeV 2  Amplitude measured in nπ + channel, for the first time  Hard A 1/2 form factor confirmed  First measurement of S 1/2, sign inconsistent with CQM  Amplitude measured in nπ + channel, for the first time  Hard A 1/2 form factor confirmed  First measurement of S 1/2, sign inconsistent with CQM  Amplitude determined up to 4.5GeV 2 using two different analysis approaches (DR, UIM)  Sign change of A 1/2  Gluonic excitation ruled out due to Q 2 dependence of both amplitudes  High Q 2 behavior consistent with radial excitation of the nucleon as in CQM  Amplitude determined up to 4.5GeV 2 using two different analysis approaches (DR, UIM)  Sign change of A 1/2  Gluonic excitation ruled out due to Q 2 dependence of both amplitudes  High Q 2 behavior consistent with radial excitation of the nucleon as in CQM Transition Form Factors

Axial Form Factors near the pion threshold region

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 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 Hall-B TJNAF 2008 Interview-Seminar Oct.16, 2008 K. Park

Differential Cross section Only S-wave contribution Hall-B TJNAF 2008 Interview-Seminar Oct.16, 2008 K. Park P.E. Bosted Phys. Rev. C 51 (1995) P.E. Bosted Phys. Rev. C 51 (1995) Assumption in LCSR V.Braun PRD77(2008) Assumption in LCSR V.Braun PRD77(2008) Due to low-energy theorem(LET) relates the S-wave multipoles or equivalently, the form factor G 1, G threshold Scherer, Koch, NPA534(1991) Vainshtein, Zakharov NPB36(1972) Scherer, Koch, NPA534(1991) Vainshtein, Zakharov NPB36(1972)

Legendre moments vs. Form Factors V.Braun Phy. Rev. D 77:034016, Hall-B TJNAF 2008 Interview-Seminar Oct.16, 2008 K. Park

Q 2 dependence of the Normalized E 0+ Multipole by dipole Preliminary Lines : MAID07 Bold : Real Thin : Imaginary Color index DNP’08 Hall-B TJNAF 2008 Interview-Seminar Oct.16, 2008 K. Park

Deep Inelastic Scattering Region Hall-B TJNAF 2008 Interview-Seminar Oct.16, 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) Hall-B TJNAF 2008 Interview-Seminar Oct.16, 2008 K. Park

Analysis Steps for 9 xbj bins CRS with low t ACC CRS with high t ACC Preliminary DNP’07 Hall-B TJNAF 2008 Interview-Seminar Oct.16, 2008 K. Park

GPD can not describe Non-perturbative part Baryon →π transition - J.P. Lansberg, B. Pire, PRD75, (2007) Pert. Kinematical variables Backward angle constraint Hall-B TJNAF 2008 Interview-Seminar Oct.16, 2008 K. Park

Analysis Steps Fit function Extracting power factor : B Preliminary Slope of fit : B Slope parameter vs. -t Horizontal red line = -8 DNP’07 Hall-B TJNAF 2008 Interview-Seminar Oct.16, 2008 K. Park

Charged double pions photoproduction Hall-B TJNAF 2008 Interview-Seminar Oct.16, 2008 K. Park

The goal of analysis is whether G11 features the isospin 3/2 in u-channel for the backward angle via γ p →Δ ++ π - ChannelIsospin γd → pn I u = 1/2 : unique γp → Δ ++ π - I u = 3/2 : unique Essential Requirements E lab >5.0 GeVu min > u > -1.5GeV 2 Nucl. Phys. B 30(1971), E. L. Berger, G. C. Fox Neutron Detection Efficiency Issue in CLAS MotivationMotivation Reactionu[GeV 2 ]t[GeV 2 ]E γ [GeV]Q 2 [GeV 2 ]PersonYear γp → nπ < u < 0.05 θ L = 140 o 2.8, 4.3, 6.7, R. Anderson1968 γp → nπ < u < 0.1 θ L = 140 o 4.3, 5.0, 9.5, R. Anderson1969 γp → pπ < u < 0.0 θ L = 140 o 6.0, 8.0, 12.0, D. Tompkins1969 Comparative Evaluation of Theories of πN Backward Scattering by E.L. Berger G. C. Fox1971 γ * p → nπ < u < < t < -3.4E e = ~ 4.35K. Park2007 γp → pπ < √s < < cosθ L < ~ M. Sumihama2007 γp → Δ ++ π < cosθ L < ~ G11a2008 Hall-B TJNAF 2008 Interview-Seminar Oct.16, 2008 K. Park

G11 photon energy coverage E 3 dσ/du E lab u = -1.7GeV 2 u = 0 I u = 3/2 exchange (Δ δ ) I u = 1/2 exchange (N α ) Hall-B TJNAF 2008 Interview-Seminar Oct.16, 2008 K. Park

w/o rho, delta++ separation Breit-Wigner fit for peak 4 th order of poly. fit for BG w/o rho, delta++ separation Breit-Wigner fit for peak 4 th order of poly. fit for BG Cross section Hall-B TJNAF 2008 Interview-Seminar Oct.16, 2008 K. Park Preparing Internal CLAS-note Preliminary

 We measured the differential cross section with extended – t region (Analysis Review will be going on sooner or later)  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 )  We measured the differential cross section with extended – t region (Analysis Review will be going on sooner or later)  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 ) SummarySummary  Extract cross sections near the pion threshold region  First time extract the very preliminary E 0+ /G D for nπ+ channel (Analysis Note will be available sooner or later)  Extract cross sections near the pion threshold region  First time extract the very preliminary E 0+ /G D for nπ+ channel (Analysis Note will be available sooner or later)  Single pion electroproduction helped to reveal the transition form factor in deeper level. –PRC 77, (2008)  Transition Form Factors has been extracted in P11(1440 ) – PRL :arXiv:080447[nucl-ex] (2008)., S11(1535) and D13(1520) - PR.  Large effort underway at EBAC to develop the coupled channel analysis of CLAS and other data – N* workshop’08  Single pion electroproduction helped to reveal the transition form factor in deeper level. –PRC 77, (2008)  Transition Form Factors has been extracted in P11(1440 ) – PRL :arXiv:080447[nucl-ex] (2008)., S11(1535) and D13(1520) - PR.  Large effort underway at EBAC to develop the coupled channel analysis of CLAS and other data – N* workshop’08 Hall-B TJNAF 2008 Interview-Seminar Oct.16, 2008 K. Park

 Polarization data to improve resonance separation  An extensive program is underway with polarized photon beams and polarized target to search for new baryon states  Proposal for a transition form factor program at high Q 2 for the CLAS 12 GeV upgrade  Full LQCD simulations with high precision planned for high Q2 is critical  Polarization data to improve resonance separation  An extensive program is underway with polarized photon beams and polarized target to search for new baryon states  Proposal for a transition form factor program at high Q 2 for the CLAS 12 GeV upgrade  Full LQCD simulations with high precision planned for high Q2 is critical FutureFuture Polarization measurement is very important !!! Hall-B TJNAF 2008 Interview-Seminar Oct.16, 2008 K. Park

Hall-B TJNAF 2008 Interview-Seminar Oct.16, 2008 K. Park