exclusive and electro-production at high q 2 in the resonance region mark jones jefferson lab...
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Exclusive po and h electro-production at high Q2 in the resonance region
Mark JonesJefferson Lab
DNP 2010Santa Fe, NM
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Baryon form factors
Measure Q2 dependence of baryon form factor dataMap out the spatial densities of the nucleonAddress the role of meson cloudStudy the transition from meson/baryon degrees of freedom to the asymptotic regime
Knowledge of form factors complements nucleon FFP33(1232) I = 3/2 J = 3/2 Decays to pN with 99% BR• Can be excited by M1, E2 and S1 multipoles• M1 dominates
S11(1535) Negative parity partner I = 1/2 J =1/2 Decays to hN with 55% BR• A1/2 helicity amplitude dominates over S1/2
N ?
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Magnetic FF, G*M, for P33(1232)
Previous Experimentsp(e;e0p)¼±
I. G. Aznauryan, V. D. Burkert, the CLAS Collaboration Phys.Rev.C80:055203,2009
Two frameworks used to extract multipoles from experimental data• Fixed-t dispersion relations• Unitary Isobar Model (UIM)
E2/M1 for P33(1232)
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Magnetic FF, G*M, for P33(1232)
Previous Experimentsp(e;e0p)¼±
E2/M1 for P33(1232)
New Hall C data •cross sections for W = 1.08 to 1.4 GeV• Full q* and f* at Q2 = 6.4 GeV2, partial at Q2 = 7.7 GeV2
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Helicity Amplitude A1/2 for S11(1535)
Previous Experiments
New Hall C data•cross sections for W = 1.50 to 1.59 GeV•Full q* and f* at Q2 = 5.7 GeV2,•partial coverage at Q2 = 7.0 GeV2
p(e;e0p)´
At very large Q2 expectQ3A1/2 to be a constant.
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Hall C Experiment 00-102SOS detected electrons
Q2 = 6.4 QSOS = 47.5
Q2 = 7.7 QSOS = 70.0
5.5 GeV e- Beam
SOS
HMSdetectedproton
4cm LH2
Angular acceptance3o in-plane
6o out-of-plane
Q2 QHMS PHMS
6.4 11.2 to 24 2.3 to 4.7
7.7 11.2 to 14 3.2 to 4.7
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e g*
Identifying exclusive channels
W
D
S11
q
P’
Mx
Qee’
Qpq
poh
Eliminate radiated elastic events with cut on fcm =180
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e g*
Identifying exclusive channels
W
D
S11
q
P’
Mx
Qee’
Qpq
poh
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e g*
Identifying exclusive channels
W
D
S11
q
P’
Mx
Qee’
Qpq
poh
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Meson Production in gp center of mass
f*
Scattering plane
Reactionplane
g
po
p’
pq* Boost from
Center of Mass to LAB
At Q2 = 6.4 GeV2
Qcm = 90o Qpq = 3.7o
d¾d ? =¾T +²¾L +²¾T T cos2Á? +
p2²(1+²)¾L T cosÁ?
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po production c.m. cross section
d¾d ?
= Ao+A1cosµ? +A2 cos2µ? +²Bo cos2Á? sin2µ?
+p2²(1+²) cosÁ?(Co+C1 cosµ?) sinµ?
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Truncated Multipole AnalysisQ2 = 6.4 GeV2
•Large M1- and E0+ so M1 dominance is not viable• Need to use cross section data in global analysis framework like UIM to reliably extract multipoles
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D Magnetic Form factor
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P33 2/ 1E M
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Multipion subtraction in h productionW = 1.5 GeV cosµ?´ = ¡ 0:92 cosµ?´ =0:42
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h production cross section
Q2 = 5.7data
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h production cross section
Q2 = 7.0 dataFit with
d¾d ? =Ao+A1 cosµ?
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h total cross section
Simultaneous fit both data sets with relativistic Breit-Wigner.
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Q2 dependence of A1/2 for S11
New Jlab Data
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Summary
Measured Full Qcm and fcm for W = 1.08 to 1.4 GeV at Q2 = 6.4 GeV2
Partial Qcm and fcm for W = 1.08 to 1.4 GeV Q2 = 7.7 GeV2
Determine G*M, E2/M1 in global UIM analysisA. N. Villano et al, Phys.Rev.C80:035203,2009
ArXiv:0906.2839v2 has UIM analysis results
Measured Full Qcm and fcm for W = 1.50 to 1.59 GeV at Q2 = 5.7 GeV2
Partial Qcm and fcm for W = 1.50 to 1.59 GeV at Q2 = 7.0 GeV2
Determine A1/2 for S11
M. Dalton et al, Phys.Rev.C80:015205,2009
p(e;e0p)¼±
p(e;e0p)´
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Backup slides
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Elimination of elastic radiated process
Q2 = 6.4 GeV2
Simulation of elastic radiated events
Data
0:25< cosµ? <1 ¡ :4< cosµ? <0:25 ¡ 1< cosµ? < ¡ 0:4
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Hall C region
of study
Magnetic FF, G*M, for P33(1232)
In Large Nc limit with GPDs Eu and Ed from fits to proton and neutron data
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Total cross section
Q2 = 6.4 GeV2 Q2 = 7.7 GeV2
Fit total cross section with Breit-Wigner + backgroundAssume M1 dominance and extract GM