David Anez Saint Mary ’ s/Dalhousie University December 10, 2012

1. E08-010: 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 December 10, 2012

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 - December 10, 2012 2/30

3. Motivation: Constituent Quark Model • Wave functions created David Anez - December 10, 2012 3/30

4. Motivation: Constituent Quark Model • Magnetic Dipole (M1 / ) • Spin-flip • Dominant David Anez - December 10, 2012 4/30

5. Motivation: Constituent Quark Model • Electric quadrupole (E2 / ) • Coulomb quadrupole (C2 / ) • Only with virtual photons David Anez - December 10, 2012 5/30

6. Multipole Amplitudes David Anez - December 10, 2012 6/30

7. Multipole Amplitudes E1+ and S1+ at same magnitude as background amplitudes Measure ratio to dominant M1+ EMR = CMR = David Anez - December 10, 2012 7/30

8. World Data and Models David Anez - December 10, 2012 8/30

9. World Data and Models David Anez - December 10, 2012 9/30

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 - December 10, 2012 10/30

11. Response Functions Unpolarized cross section made up of four independent partial cross sections David Anez - December 10, 2012 11/30

12. Response Functions David Anez - December 10, 2012 12/30

13. Response Functions Truncated Multipole Expansion Model Dependent Extraction Fit theoretical model to existing data Insert model values for background amplitudes David Anez - December 10, 2012 13/30

14. The Experiment • Jefferson Lab, Hall A • Feb 27th – Mar 8th, 2011 • 1160 MeV e− beam • 4 & 15 cm LH2 target • Two high resolution spectrometers • HRSe and HRSh David Anez - December 10, 2012 14/30

15. 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 - December 10, 2012 15/30

16. Original Kinematic Settings David Anez - December 10, 2012 16/30

17. Revised Kinematic Settings David Anez - December 10, 2012 17/30

18. Actual Kinematic Settings 85% 85% David Anez - December 10, 2012 18/30

19. Calibrations – Beam Current • BCM Calibration Runs • Kinematic 2, March 3rd • 80 µA to 0.2 µA • CODA Run 2252, MCC Run 170 • Match Faraday Cup Current to OLO2 Current • CODA Run 2254, MCC Run 173 • Match BCM Voltages to OLO2 Current • Bypassed Unser Coil David Anez - December 10, 2012 19/30

20. Calibrations – Beam Position • BPM Calibration Runs • Feb 19th – Runs 1579-1599 • May 4th – Runs 4139-4149 • BPM Code • Determine pedestals • Measure means • Calculate coefficients • Check calculations • Determine raster constants David Anez - December 10, 2012 20/30

21. Calibrations – Boiling Test • Boiling Test Runs • Kinematic 12, Mar 6th • Runs 2439-2447 • 10 µA to 80 µA, 4cm target • HAPPEX Luminosity Scintillators • Downstream of target David Anez - December 10, 2012 21/30

22. Calibrations – Vertical Drift Chambers • VDC Code • Find maximum • Find largest slope David Anez - December 10, 2012 22/30

23. Calibrations – Mispointing • Target and Optical Survey • JLab Alignment Group • Feb 11th • BeO Target Runs • Each kinematic David Anez - December 10, 2012 23/30

24. Calibrations – RHRS Gas Cerenkov Particle Identification – Electrons David Anez - December 10, 2012 24/30

25. Calibrations – LHRS Pion Rejector Particle Identification – Protons David Anez - December 10, 2012 25/30

26. Calibrations – RHRS Shower/Preshower Particle Identification – Electrons David Anez - December 10, 2012 26/30

27. Coincidence Timing Online Analysis Difference of BB T3 & T1 Offline Analysis Difference of LHRS T3 & T1 S2m Timing Difference David Anez - December 10, 2012 27/30

28. Coincidence Timing • LHRS Double Peak Problem • Due to S1 miswiring • RHRS Double Peak Problem • Due to S2 miswiring • Both solved by subtracting local T1 David Anez - December 10, 2012 28/30

29. Coincidence Timing • Red: No other corrections, shifted +80 ns • Green: Pathlength corrections • Blue: Pathlength corrections and calibration offsets David Anez - December 10, 2012 29/30

30. Still To Do • Cut Determination • Process Raw Data • Calculate Efficiencies • Calculate Systematic Errors • Produce Simulation Data • Extract Cross Sections • Thesis – Summer 2013 • Paper – Summer 2013 David Anez - December 10, 2012 30/30

31. Motivation: Constituent Quark Model • One-body interactions • Two-body interactions

32. Motivation: Constituent Quark Model • Pion Cloud

33. 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

34. Kinematics – Electronic Vertex • Momentum transfer, Q2

35. Kinematics – Hadronic Vertex • Recoil proton • Energy Ep • Momentum pp • Angle θpq • Recoil pion • Energy Eπ • Momentum pπ • Angle θπ • Not detected

36. Kinematics – Planes • Scattering plane – ki and kf • Recoil plane – pp and pπ • Azimuthal angle – pq

37. 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 /

38. Response Functions • Unpolarized cross section made up of four independent partial cross sections