David Anez Saint Mary’s/Dalhousie University June 9, 2011

1. Measurement of the Coulomb quadrupole amplitude in the γ*p→Δ(1232) reaction in the low momentum transfer region David Anez Saint Mary’s/Dalhousie University June 9, 2011

2. Introduction • Took measurements of the p(e,e′p)π0 (pion electroproduction) reaction • In the low Q2 region where the pion cloud is expected to dominate • With center-of-mass energies near the Δ resonance to look at the transition amplitudes between the nucleon and the delta • To better understand the Coulomb quadrupole transition amplitude behavior in this region and how it affects nucleon deformation David Anez – June 9th, 2011 2/19

3. Motivation: Constituent Quark Model • Wave functions created David Anez – June 9th, 2011 3/19

4. Motivation: Constituent Quark Model • Magnetic Dipole (M1 / ) • Spin-flip • Dominant David Anez – June 9th, 2011 4/19

5. Motivation: Constituent Quark Model • Electric quadrupole (E2 / ) • Coulomb quadrupole (C2 / ) • Only with virtual photons David Anez – June 9th, 2011 5/19

6. Multipole Amplitudes David Anez – June 9th, 2011 6/19

7. Multipole Amplitudes • E1+ and S1+ at same magnitude as background amplitudes • Measure ratio to dominant M1+ • EMR = • CMR = David Anez – June 9th, 2011 7/19

8. World Data and Models David Anez – June 9th, 2011 8/19

9. World Data and Models David Anez – June 9th, 2011 9/19

10. World Data and Models • Q2 = 0.045 (GeV/c)2 • New lowest CMR value • θe = 12.5° • Q2 = 0.125 (GeV/c)2 • Validate previous measurements • Q2 = 0.090 (GeV/c)2 • Bridge previous measurements David Anez – June 9th, 2011 10/19

11. The Experiment • Jefferson Lab, Hall A • February 27th – March 8th, 2011 • 1160 MeV e− beam • 4 & 15 cm LH2 target • Two high resolution spectrometers • HRSe and HRSh David Anez – June 9th, 2011 11/19

12. High Resolution Spectrometers • Vertical drift chambers • Particle tracking • Scintillators • Timing information • Triggering DAQ • Gas Cerenkov detectors • Particle identification • Lead glass showers • Particle identification David Anez – June 9th, 2011 12/19

13. Original Kinematic Settings David Anez – June 9th, 2011 13/19

14. Revised Kinematic Settings David Anez – June 9th, 2011 14/19

15. Actual Kinematic Settings 85% 85% David Anez – June 9th, 2011 15/19

16. Response Functions • Unpolarized cross section made up of four independent partial cross sections David Anez – June 9th, 2011 16/19

17. Response Functions David Anez – June 9th, 2011 17/19

18. Response Functions • Truncated Multipole Expansion • Model Dependent Extraction • Fit theoretical model to existing data • Insert model values for background amplitudes David Anez – June 9th, 2011 18/19

19. Work Still to Do • Calibration Analysis: May 2011 • Data Analysis: January 2012 • Doctoral Thesis: December 2012 • Published Paper: 2014? David Anez – June 9th, 2011 19/19

20. Motivation: Constituent Quark Model • One-body interactions • Two-body interactions David Anez – June 9th, 2011

21. Motivation: Constituent Quark Model • Pion Cloud David Anez – June 9th, 2011

22. Kinematics – Electronic Vertex • Incoming electron • Energy E • Momentum ki • Scattered electron • Energy E′ • Momentum kf • Angle θe • Virtual photon • Energy ω • Momentum q • Angle θq David Anez – June 9th, 2011

23. Kinematics – Electronic Vertex • Momentum transfer, Q2 David Anez – June 9th, 2011

24. Kinematics – Hadronic Vertex • Recoil proton • Energy Ep • Momentum pp • Angle θpq • Recoil pion • Energy Eπ • Momentum pπ • Angle θπ • Not detected David Anez – June 9th, 2011

25. Kinematics – Planes • Scattering plane – ki and kf • Recoil plane – pp and pπ • Azimuthal angle – pq David Anez – June 9th, 2011

26. Multipole Amplitudes • General form of πN Multipoles: • X – type of excitation (M, E, S) • I – isospin of excited intermediate state • ℓ± – JΔ = ℓ ± 1⁄2 • Magnetic dipole – M1 / • Electric quadrupole – E2 / • Coulomb quadrupole – C2 / David Anez – June 9th, 2011

27. Response Functions • Unpolarized cross section made up of four independent partial cross sections David Anez – June 9th, 2011

28. Response Functions • Unpolarized cross section made up of four independent partial cross sections David Anez – June 9th, 2011

29. Original Phase Space PlotsQ2 = 0.041 (GeV/c)2 (θpq* = 30°) W vs θpq* W vs Q2 Q2 vs θpq* Q2 vs θpq* W± 5MeV

30. Original Phase Space PlotsQ2 = 0.090 (GeV/c)2 (θpq* = 40°) W vs θpq* W vs Q2 Q2 vs θpq* Q2 vs θpq* W± 5MeV

31. Original Phase Space PlotsQ2 = 0.125 (GeV/c)2 (θpq* = 30°) W vs θpq* W vs Q2 Q2 vs θpq* Q2 vs θpq* W± 5MeV

32. Original Phase Space PlotsQ2 = 0.125 (GeV/c)2 (θpq* = 55°) W vs θpq* W vs Q2 Q2 vs θpq* Q2 vs θpq* W± 5MeV

33. Revised Phase Space PlotsQ2 = 0.045 (GeV/c)2 (θpq* = 33°) W vs θpq* W vs Q2 Q2 vs θpq* Q2 vs θpq* W± 5MeV

34. Revised Phase Space PlotsQ2 = 0.090 (GeV/c)2 (θpq* = 45°) W vs θpq* W vs Q2 Q2 vs θpq* Q2 vs θpq* W± 5MeV

35. Revised Phase Space PlotsQ2 = 0.125 (GeV/c)2 (θpq* = 30°) W vs θpq* W vs Q2 Q2 vs θpq* Q2 vs θpq* W± 5MeV

36. Revised Phase Space PlotsQ2 = 0.125 (GeV/c)2 (θpq* = 55°) W vs θpq* W vs Q2 Q2 vs θpq* Q2 vs θpq* W± 5MeV