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Adrian Sindile - University of New Hampshire

Proton Form Factor Ratio Measurement with BLAST. Adrian Sindile - University of New Hampshire. Ph.D. Thesis Defense – April 3, 2006. Outline of Presentation. - Overview and Motivation - Introduction - Existing Methods & Data - Phenomenological Fits - Theoretical Models

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Adrian Sindile - University of New Hampshire

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  1. Proton Form Factor Ratio Measurement with BLAST Adrian Sindile - University of New Hampshire Ph.D. Thesis Defense – April 3, 2006

  2. Outline of Presentation - Overview and Motivation - Introduction - Existing Methods & Data - Phenomenological Fits - Theoretical Models - Experimental Apparatus - Bates Linac - Polarized Target - BLAST Detector - DAQ • - Data Analysis • - Event Selection • - Data Quality • - Monte Carlo • - Results • - Asymmetries • - μGEp/GMp • - Systematic errors - Discussion and Outlook

  3. Introduction - Matter is made of atoms… - The heart of the atom is the nucleus - Nuclei contain protons and neutrons – or collectively, nucleons - Goals are to test theories of nuclear structure - What is the nature of the NN interaction? - How do we describe nuclear structure?

  4. E & M in the Nucleon • Electricity and Magnetism in the Nucleon Form Factors GE, GM • Fundamental quantities describing charge/magnetization in the nucleon • Test of QCD based calculations and models • Provide basis for understanding more complex systems in terms of quarks and gluons • Necessary for parity-violation experiments • Proton is easiest to study

  5. Form Factors - Form Factor definition - Nucleon current - Fourier Transforms in Breit Frame 1, for Q2 0 2.79, for Q2 0; τ = Q2/4M2

  6. Existing Methods – Unpolarized X-Section Rosenbluth Separation: - Mott cross section describes the scattering of a spin ½ electron off a spinless, point-like nucleon: - For Q2 > 1 (GeV/c)2 the electric form factor is difficult to measure - At low Q2, the magnetic form factor becomes difficult to extract

  7. World Unpolarized Data - GEp

  8. World Unpolarized Data - GMp

  9. Existing Methods – Polarization Transfer - Polarization transfer measurements use a Focal Plane Polarimeter (FPP) - Pt and Pl of the scattered proton are measured simultaneously (using 12C) - GEp/GMp is measured directly:

  10. GEp/GMp – Unpolarized Data

  11. GEp/GMp – Polarized Data

  12. Phenomenological Fits

  13. Pion Cloud - Just like particles appear in vacuum… - Pion as a pair of quarks … pions pop up continuously at the nucleon surface - Pion contribution can be revealed in e-N scattering

  14. Two-Photon Exchange Contributions - Guichon and Vanderhaegen (2003): although small (few %) the 2-photon effect is accidentally amplified in the Rosenbluth method! - Blunden et al. (2003) did a first model-dependent calculation of the 2-photon effect and found small corrections with strong angular dependence at fixed Q2 , proving significant for the Rosenbluth method – they explained about half of the discrepancy!! - Chen et al.(2004)related the 2-photon effect to the GPD and resolved most of the discrepancy between unpolarized and polarized data!!!

  15. Theoretical Calculations • - Direct QCD calculations • - pQCD scaling at high Q2 • - Lattice QCD • - Meson Degrees of Freedom • - Dispersion analysis, Höhler et al. 1976 • - Vector Meson Dominance (VMD), Lomon 2002 • - Soliton Model, Holzwarth 1996 • - QCD based constituent quark models (CQM) • - LF quark-diquark spectator, Ma 2002 • - LFCQM + CBM, Miller 2002

  16. Theoretical Models

  17. BLAST - Underlying Idea - Capitalize on the magnetism of the nucleus - We can polarize a collection of nuclei - Polarization observables will manifest themselves!

  18. BLAST - Underlying Idea • Goal of BLAST was to map GEp/GMp in the low Q2 region of the pion cloud • Systematics different from Polarization Transfer Method • insensitive to Pb and Pt • Q2 = 0.1 – 0.9 (GeV/c) 2 • input for P.V. experiments • Exploits unique features of BLAST • internal target: low dilution, fast spin reversal • large acceptance: simultaneously measure all Q2 points • symmetric detector: super-ratio measurement

  19. The Super Ratio Technique - Differential cross section for longitudinally polarized electrons scattered from a polarized proton target: - Spin-Dependent Asymmetry: - Experimental Spin-Dependent Asymmetry: - Super Ratio: - Beam and target polarizations cancel out in the super ratio !

  20. Experimental Setup - Polarized Beam • Polarized Source • Linac • Recirculator • South Hall Ring (SHR) • Siberian Snakes • BLAST detector in SHR • ABS: BLAST target embedded in the beamline • Storage Ring • E = 850 MeV • Imax=225 mA • Pb = 0.65

  21. Experimental Setup - Atomic Beam Source • Internal ABS Target • 60 cm storage cell • t = 4.91013 cm-2 • Pt = 0.80 - pure internal target - high polarization, fast spin reversal - L = 3.1  1031 cm-2s-1

  22. 1 1 1 1 MFT (2->3) 3 3 2 2 nozzle 4 6-pole 6-pole Experimental Setup - Atomic Beam Source • Standard technology • Dissociator & nozzle • 2 sextupole systems Spin State Selection:

  23. BEAM DRIFT CHAMBERS TARGET CERENKOV COUNTERS BEAM NEUTRON COUNTERS SCINTILLATORS BLAST Detector Package • - Large Acceptance • 20o < θe < 120o • - 22o < φe < 22o • 0.1 (GeV/c)2< Q2 < 0.9 (GeV/c)2 • - Wire Chamber Tracking • pe /pe  3 • e  0.° • z  1 cm • - BLAST Field • Bmax = 3.8 kG • - Cerenkov Detectors for PID • - Scintillators for Time-Of-Flight

  24. BLAST Time-of-Flight System - scintillating material: BC-408 (Bicron) - dimensions (cm): - backward angle: 180 - 26.10 - 2.54 - forward angle: 120 - 17.8 - 2.54 - light-guides: BC-800 - optical adhesive: OP-21G (Dymax) - 3” PMTs - 9822 (Electron Tubes) - active (transistorized bases) - optical grease: BC-630

  25. BLAST Time-of-Flight System • - Fast Timing Information • TDC – 50 ps/ch • important for BLAST trigger • - Energy Information • ADC – 50 fC/ch • - Performance • efficiency > 99% • δT < 500 ps FWHM

  26. BLAST Trigger and DAQ - NIM and CAMAC electronics - 16 bit Sector MLUs - XMLU and Trigger Supervisor - Fastbust TDCs and ADCs

  27. BLAST Relational Database RUN TRIGGER CC_ADC_RUN CC_TDC_RUN SC_ADC_RUN SC_TDC_RUN CC_ADC CC_TDC SC_ADC SC_TDC CC_PMT SC_PMT SC_HV CC CC_HV SC

  28. BLAST Reconstruction • Scintillators - timing, calibration • Wire chamber - hits, stubs, segments - link, track fit • Data Summary Tape - ep_skim: ROOT Tree

  29. Event Selection – WC Region

  30. Event Selection – WC Region

  31. Event Selection – WC Region • AfterWC misalignment fixed

  32. Event Selection – WC Region

  33. Event Selection – BAT Region If outside WC Timing Cuts + Cerenkov Cuts!

  34. Event Selection – BAT Region TOF = (LeftTOP + LeftBOT)/2 - (RightTOP + RightBOT)/2 POS = (LeftTOP - LeftBOT) + (RightTOP - RightBOT)

  35. Data Quality

  36. Results - Asymmetries BLAST Left Sector BLAST Right Sector

  37. Results – Form Factor Ratio μGEp/GMp compared to Hoehler’s Parametrization

  38. Results – Systematic Errors - Super Ratio: Spin Angle & Tracking Contributions to Systematics

  39. Results – Systematic Errors Q2 Discrepancy Contributions to Systematics

  40. Results – Systematic Errors Major Contributions to Systematic Errors

  41. Results – Form Factor Ratio μGEp/GMp

  42. Results – Form Factor Ratio μGEp/GMp

  43. Results – Form Factor Ratio μGEp/GMp

  44. Summary • 1st measurement of mGEp/GMp using a polarized beam and a polarized target • improvement in precision of mGEp/GMp at Q2 = 0.1– 0.5 GeV2 • sensitive to the pion cloud • narrow dip around Q2=0.2-0.3 GeV2 ? • systematic errors are being reduced • further reducing the statistical errors for the last data point is possible

  45. THANK YOU! R. Alarcon, E. Geis, J. Prince, B. Tonguc, A. Young Arizona State University  J. Althouse, C. D’Andrea, A. Goodhue, J. Pavel, T. Smith, Dartmouth College T. Akdogan, W. Bertozzi, T. Botto, M. Chtangeev, B. Clasie, C. Crawford, A. Degrush, K. Dow, M. Farkhondeh, W. Franklin, S. Gilad, D. Hasell, E. Ilhoff, J. Kelsey, M. Kohl, H. Kolster, A. Maschinot, J. Matthews, N. Meitanis, R. Milner, R. Redwine, J. Seely, A. Shinozaki, S.Sobczynski, C. Tschalaer, E. Tsentalovich, W. Turchinetz, Y. Xiao, H. Xiang, C. Zhang, V. Ziskin, T. Zwart Massachusetts Institute of Technology Bates Linear Accelerator Center D. Dutta, H. Gao, W. Xu Duke University J. Calarco, W. Hersman, M. Holtrop, T. Lee O. Filoti, P. Karpius, A. Sindile University of New Hampshire J. Rapaport Ohio University K. McIlhany, A. Mosser United States Naval Academy  J. F. J. van den Brand, H. J. Bulten, H. R. Poolman Vrije Universitaet and NIKHEF W. Haeberli, T. Wise University of Wisconsin BLAST Collaboration

  46. Results – Systematic Errors Beam Asymmetry: Target Asymmetry: False Asymmetries Contributions to Systematics

  47. Results – Systematic Errors - background: about 0.8% of the total event number - it acts only as dilution, it cancels to first order in super-ratio - radiative effects: Background and Radiative Effects Contributions to Systematics

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