Recent Results from Jefferson Lab Experiments APCTP Workshop Wooyoung Kim Kyungpook National University

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

Thomas Jefferson National Accelerator Facility

The CEBAF Large Acceptance Spectrometer in Hall B

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

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

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

Fπ deviates from the charge-radius constrained monopole form atthese values of Q 2 by one σ Fπ far from its pQCD prediction

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, R EM (EMR)  A non-zero Value for EMR : Clear Evidence for “Deformation” Virtual Photon ;  E2, C2(Coulomb, or Scalar), R EM (EMR), R SM (CMR) N-Δ Transition arXv:hep-ex/ v1 19Jun 2006

Proton Structure R EM > 0 R EM < 0

Asymmetry measurements

Q 2 dependence of the electric (E 1+ ) and scalar (S 1+ ) quadrupole/magnetic dip ole ratios from this experiment(dots) Structure function versus cosθ * π extracted for the p(e,e / p)π 0 reac- tion at Q 2 =0.9 GeV 2.

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).

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 G C (Q 2 ) and electric quadrupole form factors. Near Q 2 =0, G C (0) determined from G E (0) using the long wavelength limit. (Siegert’s Thm).  T. Sata and T. S. Lee, PRC 63, (2001)  S. S. Kamalov and S. N. Yang, PRL 83, 4494 (1999)  “Pion cloud effects dominate the quadrupole transition”

A LT / - measurements Beam asymmetry A LT / vs φ π * for the reaction at Q 2 =0.40 GeV 2 and W=1.22 GeV. for π 0 p channel (top) and for π + n channel (bottom), extracted at Q 2 =0.40 GeV 2 and W= GeV ALT/- measurementsALT/- measurements

magnetic form factor decreases with Q 2 faster than the proton magnetic form factor

R EM is small and negative, indicating strong helicity non- conservation R SM is negative, while its magnitude increases with Q 2 The results confirm the absence of pQCD scaling at these kinematics

Electron Beam Asymmetry E = GeV W=1.40, Q 2 = 2.05GeV 2 φ CM A LT ’ MAID00 MAID03 SL04 SL Roper Resonance Kijun Park Ph. D. Thesis KNU (2006)

MAID00 MAID03 SL04 SL Δ(1232) P 11 (1440) S 11 (1535) F 15 (1680)

Structure Function MAID00 MAID03 SL04 SL Δ(1232) P 11 (1440) S 11 (1535) F 15 (1680)

Structure Function MAID00 MAID03 SL04 SL Δ(1232) P 11 (1440) S 11 (1535) F 15 (1680)

MAID00 MAID03 SL04 SL Δ(1232) P 11 (1440) S 11 (1535) F 15 (1680)

Photocoupling Amplitude A 1/2, S 1/2 Quark Models This Work GWU (VPI) pion photoproduction RPP etimation η electro-, photo- production IM, DR π electro- production IM, DR Relativistic Quark Model Nonerlativistic Quark Model Bonn, DESY, NINA, Jlab( η ) Light-front calculation q 3 G hybrid state

GPDs 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(Q 2 →∞, x B 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) DVCS arXiv:hep-ex/ v3 3Jul 2006

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, Q 2 > 1 (GeV/c) 2 )

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

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 negative beam helicity

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

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.

Longitudinal Target-Spin Asymmetry A uL measured for e p e'p ϒ with 5.72 GeV electron beams

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

where,, H, and E are sums over quark flavor of the corresponding GPDs with argument,F 1 and F 2 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.

12GeV Upgrade Time Resolution : 60 ps Plastic : Bicron BC-408 PMT Assembly : Hamamatsu H High Magnetic Field : 5 Tesla High Energy : 12 GeV High Luminosity : /cm 2 sec 50 pieces Barrel Detector Design, Development and Test Micro Channel Plate PMT

Barrel Plastic Scintillator Prototype

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-Q 2 data is obtained.