recent results from jefferson lab experiments apctp workshop 2007. 2. 28 wooyoung kim kyungpook...
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Recent Results from Jefferson Lab Experiments
APCTP Workshop2007. 2. 28
Wooyoung KimKyungpook National University
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OutlineOutline
Jefferson Lab, CLAS, Detector, KNU Contribution Pion Form Factor N-△ Transition Roper Resonance DVCS with Polarized Proton Target 12 GeV Upgrade
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Thomas Jefferson National Accelerator Facility
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The CEBAF Large Acceptance Spectrometer in Hall B
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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
0 ,
( , ' )p e e n
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Pion Form Factor arXv:nucl-ex/0607005 v1 7Jul 2006
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
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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
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Fπ deviates from the charge-radius constrained monopole form atthese values of Q2 by one σ
Fπ far from its pQCD predi
ction
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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 allo
ws 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)
N-Δ Transition arXv:hep-ex/0606042 v1 19Jun 2006
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Proton Structure
REM > 0
REM < 0
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Asymmetry measurements
/
*
*
: Re( ) Re( ) Re( ) Im( ) Im( )
: Im( ) Re( ) Im( ) Im( ) Re( )
LT
LT
LT L T L T
LT L T L T
/m
LTe
m
AA
P
N NA
N N
/
*2 2* *
0* *2 (1 ) sin sinL LT
pdh
d k
2 * *
0
* *
sin cos 2
2 (1 ) sin cos
T L L TT
L LT
/
/
* *2 2
2 20
2 (1 ) sin sinL LTLT
d dA
d d
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Q2 dependence of the electric (E1+) and scalar (S1+) quadrupole/magnetic dipole ratios from this experiment(dots)
Structure function versus cosθ*
π extracted for the p(e,e/ p)π0 reac-tion at Q2 =0.9 GeV2 .
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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).
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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”
*N
(1232)N
2( )EG Q N
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ALT/- measurements
( , )p e e n Beam asymmetry ALT / vs φπ
* for the reaction at Q 2 =0.40 GeV2
and W=1.22 GeV.
for π0p channel (top) and for π+n channel (bottom), extracted at Q2 =0.40 GeV2 and W=1.18-1.26 GeV
*cosLT vs
AL
T/
- measurements
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magnetic form factor
decreases with Q2 faster than the proton magnetic form factor
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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
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Electron Beam Asymmetry
E = 5.754 GeVW=1.40, 1.69GeV @ Q2= 2.05GeV2
φCM φCM
A LT’
A LT’
MAID00
MAID03
SL04SL
Roper Resonance Kijun Park Ph. D. Thesis KNU (2006)
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Structure Function
MAID00
MAID03
SL04SL
Δ(1232)
P11(1440)
S11(1535)
F15(1680)
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Structure Function MAID00
MAID03
SL04SL
Δ(1232)
P11(1440)
S11(1535)
F15(1680)
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Structure Function MAID00
MAID03
SL04SL
Δ(1232)
P11(1440)
S11(1535)
F15(1680)
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Structure Function // MAID00
MAID03
SL04SL
Δ(1232)
P11(1440)
S11(1535)
F15(1680)
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Photocoupling Amplitude A1/2 , S1/2
Quark Models
This Work
GWU (VPI) pion photoproduction
RPP etimation
ηelectro-, photo- production IM, DR
π electro- production IM, DR
Relativistic Quark ModelNonerlativistic Quark ModelBonn, DESY, NINA, Jlab(η)
Light-front calculation
q3G hybrid state
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GPDs Formalism for the QCD description of deeply exclusive leptoproduc
tion 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)
DVCS arXiv:hep-ex/0605012 v3 3Jul 2006
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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)
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Feynman diagrams for DVCS and Bethe-Heitler processes contributing to the amplitude of scattering ep ep
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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
42
2
4 4
2 2
1,1 0,12
| |
Im( )
1 Im sin Im sin 2
DVCS BH
B
DVCS BH
B B
dT T
dQ dx dtd
d dT T
dQ dx dtd dQ dx dtd
a M b M OQ
4 4
4 4
( )1
( )e
N Nd dA
d d P N N
ePN
N
ep ep
ep ep
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The data points are fitted with the function The fitted parameters are
In the Bjorken regime should vanish, leaving only the contri
bution from transverse photons.
Theoretical calculations are from fixed values of
( ) sin sin 2 .A
0.202 0.028 0.013 ,
0.024 0.028 0.009 .
stat sys
stat sys
2 2
2
1.25 ( / ) ,
0.19,
0.19
B
Q GeV c
x
t GeV
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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.
( )A
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Longitudinal Target-Spin Asymmetry AuL measured for
e p e'p ϒ with 5.72 GeV electron beams
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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 increase
s with increasing , in agreement with model prediction
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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.
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12GeV Upgrade
•Time Resolution : 60 ps• Plastic : Bicron BC-408•PMT Assembly : Hamamatsu H2431-50
•High Magnetic Field : 5 Tesla•High Energy : 12 GeV•High Luminosity : 1035 /cm2sec
50 pieces Barrel Detector Design, Development and Test
Micro Channel Plate PMT
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Barrel Plastic Scintillator Prototype
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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.