Diapositive 1

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Genoa, 25/02/09
Electron scattering in CLAS (selected) review
M. Guidal, IPN Orsay
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Nucleon ground state
Nucleon resonances
unpolarized
polarized
AUL, ALL, ALU for p SIDIS
DVCS
Vector meson
Color tranparency
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Many thanks, for the slides, to
M. Aghasyan (SIDIS), H. Avakyan (SIDIS), V.
Burkert (FFs), E. Christy (DIS), W. Gohn
(SIDIS), K. Hafidi (Nuclear), N. Guler (DIS), S.
Kuhn (DIS).
N,Spin08,ECT workshop,CLAS Coll.meetings,
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Nucleon ground state
Nucleon resonances
unpolarized
polarized
AUL, ALL, ALU for p SIDIS
DVCS
Vector meson
Color tranparency
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Ground state and Transition Form Factors
,
e
e
g
N
N,N
Np,n
GE ,GM
GE ,GM ,GC
(or E1 ,M1 ,S1)
ND(1232) P11(1440) D13(1520)
S11(1535)
pN
pN,ppN
(or A1/2 ,S1/2)
GE ,GM
pN,ppN
(or A1/2 ,A3/2 ,S1/2)
GE ,GM ,GC
hN,pN
(or A1/2 ,S1/2)
GE ,GM
Electric/Magnetic/Coulomb,Multipoles, Helicity
amplitudes,
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Neutron Magnetic Form Factor
Hall B
CLAS
Real time in-situ calibration of the neutron
detection efficiency in the CLAS e.m. calorimeter
EC measured online through ep?ep(n).
Results of the neutron magnetic form factors
from Q2 1- 5 GeV2 . No large deviation
observed from dipole form. J. Lachniet et al.
(CLAS) arXiv0811.1716 (PRL)
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N? Multipole Ratios REM, RSM

• There is no sign for asymptotic pQCD behavior in
  REM (-gt1) or RSM (-gtCte).
• REM lt 0 at low Q2 favors oblate shape of ?(1232)
  and prolate shape of the proton.

• Dynamical models attribute the deformation to
  contributions of the pion cloud at low Q2.

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P11(1440) amplitudes from Np and Npp
Np
Npp (preliminary)
PDG
First observed zero crossing of a nucleon form
factor!
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Fits to diff. cross sections structure
functions
Q23.48GeV2
Q22.05GeV2
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Transition amplitudes for D13(1520)
Np
M. Dugger et al., PRC76 025211, 2007
Npp (preliminary)
A3/2
A1/2
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Transition amplitudes for D13(1520)
S1/2
CQM predictions A1/2 dominance with increasing
Q2.
Ahel
ppp- (prel.)
np
pp0
np
pp0
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Transition amplitudes for S11(1535)
This state has traditionally been studied in
the S11(1535)?p? channel, which is the prominent
decay. For the study of S1/2 Np channel is
important. S1/2 difficult to extract in p?
channel.

• A1/2 from np consistent with ph within
  uncertainties of b.r.

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Form Factors
CLAS
M. Vanderhaeghen, L. Tiator
p-gtD
p-gtS11(1535)
p-gtD13(1535)
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Transverse Charge Densities
CLAS
M. Vanderhaeghen, L. Tiator
The charge distribution of the p-Roper
transition shows a dense positive core of 0.5
fm radius, and a negative outer shell up to a
radius of 1 fm.
p-gtD
p-gtS11(1535)
p-gtD13(1535)
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Conclusions

• N?(1232) amplitudes are well determined at Q2 up
  to 6 GeV2.
• No sign of transition to asymptotic QCD behavior
• Roper P11(1440) amplitudes determined up to 4.5
  GeV2 using two different analysis approaches (DR,
  UIM), and two channels
• Sign change of A1/2 seen in Np and Npp
• S11(1535) amplitudes measured in np channel, for
  the first time
• Hard A 1/2 form factor confirmed
• First measurement of S1/2.
• D13(1520) in np and ppp-
• Helicity switch from A3/2 dominance to A1/2
  dominance at Q2gt0.6 GeV2
• First measurement of S1/2.

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Nucleon ground state
Nucleon resonances
unpolarized
polarized
AUL, ALL, ALU for p SIDIS
DVCS
Vector meson
Color tranparency
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Need proton and neutron targets to pin down u/d
PDFs from DIS
At Leading order
x4/9u(x) 1/9d(x)
x4/9d(x) 1/9u(x)
At large x proton dominated by u(x) and neutron
by d(x)? due to charge weighting.
PDFs least well known at large x Also, proton
neutron data provides way to separate valence
cleanly (Gluon comparable in size to dv at x0.3)
u(x)?
d(x)?
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• Deuterium proton data does not allow clean
  determination of neutron for x ? 1 due to nuclear
  corrections

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CLAS with the RTPC and one electron event.
to CLAS
n
p
To BoNuS RTPC
f, z from pads r from time
beam
Helium/DME at 80/20 ratio
dE/dx from charge along track (particle ID)
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Spectator Tagging
E 4.223 GeV
ltQ2gt 1.19 (GeV/c)2

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Structure function ratio
PRELIMINARY
Good agreement with previous data in smaller x
region.
Full acceptance
correction method forthcoming.
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Double polarized inclusive electron scattering
e
Long. Polarized Electron
qe
e
Pe
Pt
y
Long. Polarized Nucleon
Cross section can be expressed in terms of
virtual photon asymmetries A1 and A2.
A1
A2
Difference in the cross sections for two cases is
expressed as double spin asymmetry.
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Q2 evolution of the GDH integral

• Both Bjorken and GDH sum rules are fundamental
  sum rules

Small Q2 GDH sum rule Experiments at Mainz,
Bonn Chiral perturbation theory
Intermediate Q2 Extended GDH sum rule Several
different models Experiments at JLAB(CLAS/Hall
A/Hall C) A good test of at what distance scale
pQCD corrections and higher twist expansions will
break down and physics of confinement dominate.
?
Large Q2 Bjorken Sum rule Experiments at
CERN,SLAC,DESY Higher order QCD expansion
EG1B has good precision data with wide Q2
coverage to answer some of these questions.

• Dramatic change of sign of G1 from DIS-regime
  to the value at the real photon point.
• At low Q2 , g1(x,Q2) is dominated by resonance
  excitations.

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A1 Deuteron
?(1232)P33
A1
N(1520-35)D13/S13
PRELIMINARY
W(GeV)
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G1 Deuteron, Comparison to world data
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G1 Deuteron, Comparison to world data
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G1 Deuteron, Comparison to world data
PRELIMINARY
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G1 Proton, Comparison to world data
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G1 Proton, Comparison to world data
PRELIMINARY
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G1 Proton, Comparison to world data
PRELIMINARY
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CLAS Saturation of the strong coupling
The saturation of ?s at large distances is a
necessary condition for the application of the
AdS5/CFT correspondence that can be used to carry
out non-perturbative QCD calculations (Brodsky,
de Teramond).
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Nucleon ground state
Nucleon resonances
unpolarized
polarized
AUL, ALL, ALU for p SIDIS
DVCS
Vector meson
Color tranparency
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SIDIS (gp?pX) cross section at leading twist (Ji
et al.)
e
Boer-Mulders 1998
Kotzinian-Mulders 1996
Collins-1993
structure functions pdf fragm hard soft
(all universal)
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Longitudinal Target SSA measurements at CLAS
p1sinfp2sin2f
W2gt4 GeV2
CLAS PRELIMINARY
Q2gt1.1 GeV2
ylt0.85
0.4ltzlt0.7
MXgt1.4 GeV
p1-0.0420.015 p2-0.0520.016
p10.0820.018 p20.0120.019
p1 0.0590.010 p2-0.0410.010
PTlt1 GeV
0.12ltxlt0.48
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ALL PT-dependence
0.4ltzlt0.7
m020.25GeV2 mD20.2GeV2
M.Anselmino et al hep-ph/0608048
p A1 suggests broader kT distributions for f1
compared to g1 p- A1 may require non-Gaussian
kT-dependence for different helicities and/or
flavors
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ALU
ALU
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ALU
Results p0
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Nucleon ground state
Nucleon resonances
unpolarized
polarized
AUL, ALL, ALU for p SIDIS
DVCS
Vector meson
Color tranparency
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DVCS_at_CLAS
e
epa epg
p
JLab/ITEP/ Orsay/Saclay collaboration
420 PbWO4 crystals 10x10 mm2, l160 mm
Read-out APDs preamps
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DVCS beam spin asymmetry
JLab Hall B Collaboration, PRL 100162002,2008
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Unpolarized Cross Section
0.09lt-tlt0.2 GeV2
0.2lt-tlt0.4 GeV2
0.4lt-tlt0.6 GeV2
POTENTIAL
0.6lt-tlt1 GeV2
1lt-tlt1.5 GeV2
1.5lt-tlt2 GeV2
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r
w
f
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Background Subtraction (normalized spectra)
1) Ross-Stodolsky B-W for r0(770), f0(980) and
f2(1270) with variable skewedness parameter, 2)
D(1232) pp- inv.mass spectrum and pp- phase
space.
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sL (gLp ? prL0)
ep ? epr 0
EPJA39 (2009)
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sL (gLp ? prL0)
Regge/Laget
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ds/dt (gp ? pr0)
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N pp0
Counts/20 MeV
100 e1-dvcs statistics
pp0 invariant mass v( p p p p0)2
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Nucleon ground state
Nucleon resonances
unpolarized
polarized
AUL, ALL, ALU for p SIDIS
DVCS
Vector meson
Color tranparency
51
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PRELIMINARY
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IM(pp)
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IM(pp-)
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N ? electroproduction experiments after 1999
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2nd and 3rd nucleon resonance regions
(PDG 2006)

• Analysis tools
• Unitary isobar model (UIM), starting from MAID.
• Dispersion relations (DR), for 1-pion analysis.
• Isobar model (JM06) for 2-pion analysis with
  leading contributions as observed in the data.
  Fit to 9 independent one-dimensional projections
  of 5-dim. cross sections.

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UIM DR Fit at low high Q2
data points gt 50,000 , Ee 1.515, 1.645, 5.75
GeV
Low Q2 results I. Aznauryan et al., PRC71,
015201, 2005 PRC 72, 045201, 2005 High Q2
results on Roper I. Aznauryan et al.,
arXiv0804.0447 nucl-ex.
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Fits to diff. cross sections structure
functions
Q23.48GeV2
Q22.05GeV2
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Legendre moments for sT esL
Q2 2.05 GeV2
cos?
(1 bcos2?)
const.
DR UIM

• DR w/o P11(1440)

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Multipole amplitudes for ?p? pn
Q2 2.05 GeV2
Q2 0

• At Q21.7-4.2, resonance behavior is seen in
  these amplitudes more clearly than at Q2 0
• DR and UIM give close results for real parts of
  multipole amplitudes

Im Re_UIM Re_DR
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G3 and G5 Proton
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Comparison with Theory
Quenched Lattice QCD - E1/M1 Good agreement
within large errors. - S1/M1 Undershoots data
at low Q2. - Linear chiral extrapolations may be
naïve and/or dynamical quarks required
Dynamical Models - Pion cloud model allows
reasonable description of quadrupole ratios over
large Q2 range.
What are we learning from E/M, S/M?
Shape of pion cloud?
Deformation of N, ? quark core?
Need to isolate the first term (within model) or
go to high Q2 to study quark core.
LQCD consistent with observed rise in magnitude
with Q2 of RSM
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N-?(1232) Quadrupole Transition
SU(6) E1S10
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y
z
x
x
M.G., Polyakov, Radyushkin, Vanderhaeghen (2005)
(fm)