1. Studying baryon resonances by meson electroproduction at high Q2
Mark Jones
Hall C Staff Scientist
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2. Studying baryon resonances by meson electroproduction at high Q2
Mark Jones
Hall C Staff Scientist
Present results from Hall C E01-002
Spokepersons:
P. Bosted, V. Frolov, M. Jones, V. Kubarovsky , P. Stoler
Thesis students:
Anthony Villano, Rensselaer Polytechnic Institute, New York
Mark Dalton, University of Witwatersrand, South Africa
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3. Understanding QCD confinement
Complement nucleon form factor data.
P33(1232) I = 3/2 J = 3/2
Decays to pN with 99% BR
S11(1535) Negative parity partner I = 1/2 J =1/2
Decays to hN with 55% BR
Measure Q2 dependence of baryon form factor data
Map out the spatial densities of the nucleon
Address the role of meson cloud
Study the transition from meson/baryon degrees of freedom to the asymptotic regime
Hall C with two spectrometers focuses probing at large Q2
D(1232) and S11(1535) which can be identified by 2-body final states
High luminosity using 4cm LH2 target with 100uA beam to measure small cross sections.

4. Magnetic FF, G*M, for P33(1232)
At large Q2 ,PQCD predicts Q2GM/GD = constant
Hall C region
of study

5. E2/M1 for P33(1232)
ND transition is dominated by the magnetic dipole, M1 with electric, E2 and Coulomb , C2, transition form factors small.
At large Q2, PQCD predicts that
REM = E2/M1 = 1

6. E2/M1 for P33(1232)
ND transition is dominated by the magnetic dipole, M1 with electric, E2 and Coulomb , C2, transition form factors small.
Hall C measurement
At Q2 = 6.3
Reduce error bar by ½
Measure to Q2 = 7.7

7. S11(1535) hN Closest resonance with significant hN BR is P11(1710)
Study Q2 dependence , much slower fall-off than P33(1232)
PQCD predicts Q3A1/2 = constant at large Q2
Hall C region
of study

8. Initial electron-proton kinematicsg* p

9. Scattered electron kinematicsQe
Scattered electron kinematics determines W, Q2,q W q g* e
S11 D

10. Identifying exclusive channelsQe P’
Scattered electron kinematics determines W, Q2,q W
Qpq q g*
Combine electron and proton kinematics to determine the missing mass, Mx e Mx
S11 D

11. Identifying exclusive channelsQe P’
Scattered electron kinematics determines W, Q2,q W
Qpq q
Combine electron and proton kinematics to determine the missing mass, Mx g* e Mx po h
S11 D

12. Identifying exclusive channelsQe P’
Scattered electron kinematics determines W, Q2,q W
Qpq q
Combine electron and proton kinematics to determine the missing mass, Mx g* e Mx po h
S11 D

13. Identifying exclusive channelsQe P’
Scattered electron kinematics determines W, Q2,q W
Qpq q
Combine electron and proton kinematics to determine the missing mass, Mx g* e Mx po h
S11 D

14. Meson Production in gp center of mass
fcm
qcm
Boost from
Center of Mass to LAB
At Q2 = 1 GeV2
Qcm = 90o Qpq = 12o
At Q2 = 6.4 GeV2
Qcm = 90o Qpq = 3.7o g p
Reaction
plane
Scattering
plane po

15. SOS detected electrons
Hall C Experiment
HMS detected protons
11.2 < QHMS < 24.0
2.3 < PHMS < 4.7 GeV
SOS detected electrons
Q2 = 6.4 QSOS = 47.5
Q2 = 7.7 QSOS = 70.0
HMS
4cm
LH2
SOS
Angular acceptance
3o in-plane
6o out-of-plane
5.5 GeV e- Beam

16. po production c.m. cross section
5 Negative f* bins
W=1232 Q2 = 6.4

17. po production c.m. cross section
5 Negative f* bins
5 Positive f* bins
W=1232 Q2 = 6.4

18. po production c.m. cross section
5 Negative f* bins
5 Positive f* bins
W=1232 Q2 = 6.4
Total of 8 W bins between 1.1 to 1.4 GeV

19. Total cross section
Use MAID analysis to extract D(1232) multipoles

20. D Magnetic Form factor
New
Hall C
data

21. P33 E2/M1
New
Hall C
data

22. h production cross section
Q2 = 5.7
data

23. h total cross section
Simultaneous fit both data sets with relativistic Breit-Wigner.

24. Q2 dependence of A1/2 for S11
New Jlab Data

25. Conclusions
S11(1535)
Doubled the Q2 range of measurement s of A1/2 to Q2 = 7.0
See change in shape of Q2 dependence.

26. Conclusions
S11(1535)
Doubled the Q2 range of measurements of A1/2 to Q2 = 7.0
See change in shape of Q2 dependence.
P33(1232)
Extracted GM , E2/M1 and C2/M1 for D(1232) from a MAID analysis
Need to understand discrepancy with CLAS data at 20% level.

27. Backup slides

28. Magnetic FF, G*M, for P33(1232)
In Large Nc limit with GPDs Eu and Ed from fits to proton and neutron data
Hall C region
of study