Recent Results from Jefferson Lab Experiments APCTP Workshop 2007. 2. 28 Wooyoung Kim

1. Recent Results from Jefferson Lab Experiments APCTP Workshop 2007. 2. 28 Wooyoung Kim Kyungpook National University

2. Outline • Jefferson Lab, CLAS, Detector, KNU Contribution • Pion Form Factor • N-△ Transition • Roper Resonance • DVCS with Polarized Proton Target • 12 GeV Upgrade

3. Thomas Jefferson National Accelerator Facility

5. The CEBAF Large Acceptance Spectrometer in Hall B

6. KNU Contribution • Laser Calibration of the TOF System • Detection Efficiency of Calorimeter • Reaction Analysis Kijun Park Ph. D. Thesis • 12 GeV Upgrade of TOF System

7. arXv:nucl-ex/0607005 v1 7Jul 2006 Pion Form Factor • Charged Pion Form at Q2 =1.60 and 2.45 (GeV/c)2 • 1H (e,e’ π+)n cross section measured • The simplest hadronic system available for study • Valence structure is abound state of a quark and antiquark

8. pQCD prediction • At low Q2: VMD model provides description of Fπ Transition from “soft” to “hard” physics expected at significantly lower Q2 for Fπ than for nucleon form factor • Fπ extracted from data by comparing the separated to Regge model prediction in which Fπ is a free parameter

9. Fπ deviates from the charge-radius constrained monopole form atthese values of Q2 by one σ Fπ far from its pQCD prediction

10. N-Δ Transition arXv:hep-ex/0606042 v1 19Jun 2006 • Intrinsic Deformation of the Spin ½ Nucleon ; • Inferred from Transition Amplitudes for the N- Δ excitation • Spherical Bag Model ; • Δ+(1232) : A pure Spin-flip Transition through an M1 Excitation. • D-state admixtures in the ground state of the Nucleon and/or Δ allows the Quadrupole Excitation. • Glashow’s Suggestion ; • A New Observable, REM(EMR) • A non-zero Value for EMR : Clear Evidence for “Deformation” • Virtual Photon ; • E2, C2(Coulomb, or Scalar), REM(EMR), RSM(CMR)

11. ProtonStructure • REM > 0 • REM < 0

12. Asymmetry measurements

13. Structure function versus cosθ*π extracted for the p(e,e/ p)π0 reac- tion at Q2 =0.9 GeV2 . Q2 dependence of the electric (E1+) and scalar (S1+) quadrupole/magnetic dipole ratios from this experiment(dots)

14. Pion Deform the Proton’s Electric Charge Cloud • The photon (blue) emitted by the scattered electron (red) interacts directly with the pion cloud rather than with the quarks inside the proton • The measured shape of the deformed electric-charge cloud is slightly oblate (squashed), rather than prolate (elongated).

15. Dynamical Pion Rescattering Modes • Calculate a meson dressed vertex in terms of the underlying bare photocoupling form factors. • Fitted their dynamical model to photo-pion observables and Jlab/ Hall-C cross sections using a common parametrization for the bare charge GC(Q2) and electric quadrupole form factors. • Near Q2=0, GC(0) determined from GE(0) using the long wavelength limit. (Siegert’s Thm). • T. Sata and T. S. Lee, PRC 63, 055201 (2001) • S. S. Kamalov and S. N. Yang, PRL 83, 4494 (1999) • “Pion cloud effects dominate the quadrupole transition”

16. ALT/- measurements for π0p channel (top) and for π+n channel (bottom), extracted at Q2 =0.40 GeV2 and W=1.18-1.26 GeV Beamasymmetry ALT / vs φπ* for the reaction at Q 2 =0.40 GeV2 and W=1.22 GeV. ALT/- measurements

17. magnetic form factor decreases with Q2 faster than the proton magnetic form factor

18. REM is small and negative, indicating strong helicity non-conservation • RSM is negative, while its magnitude increases with Q2 • The results confirm the absence of pQCD scaling at these kinematics

19. MAID00 MAID03 SL04 SL Kijun Park Ph. D. Thesis KNU (2006) Roper Resonance Electron Beam Asymmetry E = 5.754 GeV W=1.40, 1.69GeV @ Q2= 2.05GeV2 ALT’ ALT’ φCM φCM

20. MAID00 MAID03 SL04 SL Structure Function Δ(1232) P11(1440) S11(1535) F15(1680)

21. MAID00 MAID03 SL04 SL Structure Function Δ(1232) P11(1440) S11(1535) F15(1680)

22. MAID00 MAID03 SL04 SL Structure Function Δ(1232) P11(1440) S11(1535) F15(1680)

23. MAID00 MAID03 SL04 SL Structure Function/ Δ(1232) P11(1440) S11(1535) F15(1680)

24. πelectro- production IM, DR ηelectro-, photo- production IM, DR RPP etimation GWU (VPI) pion photoproduction This Work Photocoupling Amplitude A1/2 , S1/2 Preliminary Relativistic Quark Model Nonerlativistic Quark Model Bonn, DESY, NINA, Jlab(η) Quark Models Light-front calculation q3G hybrid state

25. arXiv:hep-ex/0605012 v3 3Jul 2006 GPDs DVCS • Formalism for the QCD description of deeply exclusive leptoproduction reactions introduces Generalized Parton Distribution (GPDs) • Carry new Information about the dynamical degrees of freedom inside the Nucleon • In the Bjorken scaling regime(Q2→∞, xB finite), the amplitude for exclusive scattering reaction can be factorized into • A hard scattering part (exactly calcluable in pQCD) • A nucleon structure part (parameterized via GPDs – handbag approximations)

26. Deeply Virtual Compton Scattering • Virtual Compton Scattering in the Bjorken regime • Virtual Compton Scattering : Electroproduction of photons from nucleons • The cleanest way of gathering information on nucleon structure • The simplest experiment for studying GPDs (W > 2GeV, Q2 > 1 (GeV/c)2)

27. Feynman diagrams for DVCS and Bethe-Heitler processes contributing to the amplitude of scattering

28. The experiment measures the interference of DVCS and Bethe-Heitler (BH) process • Beam Spin Asymmetry where : beam polarization (70%) : number of events at positive beam helicity : number of events at negativebeam helicity

29. The data points are fitted with the function The fitted parameters are In the Bjorken regime should vanish, leaving only the contribution from transverse photons. • Theoretical calculations are from fixed values of

30. dependence of the beam spin asymmetry A. The dark shaded region is the range of the fitted function defined by the statistical errors of parameters and , the light shaded region includes systematic uncertainties added linearly to the statistical uncertainties.

31. Longitudinal Target-Spin Asymmetry AuL measured for e p e'p ϒ with 5.72 GeV electron beams

32. Theoretical calculations in good agreement with the magnitude and kinematic dependence of target-spin asymmetry, which is sensitive to GPDs and H • Leading term Aulsin increases with increasing , in agreement with model prediction

33. where, , H, and E are sums over quark flavor of the corresponding GPDs with argument ,F1 and F2 are the known Dirac and Pauli form factors of the proton, and M is the rest mass of the proton. In the range of this experiment the asymmetry is dominated by both H and , while and E are kinematically suppressed.

34. 12GeV Upgrade 50 pieces Barrel Detector Design, Development and Test Micro Channel Plate PMT

35. Barrel Plastic Scintillator Prototype

36. Summary • Results provide strong constraints on isobar-based effective Lagrangian models, or approaches employing fundamental parton degrees of freedom, such as LQCD, GPDs, LCSR, pQCD • 12 GeV Upgrade Planned • Greater theoretical progress will be necessary before good quantitative agreement with the experimental high-Q2 data is obtained.