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S pin A symmetries of the N ucleon E xperiment

Proton Form Factor Ratio , G P E /G P M From Double Spin Asymmetries. S pin A symmetries of the N ucleon E xperiment. ( E07-003). Analysis Updates. Anusha Liyanage Hall C User Meeting (January 25, 2013). Outline. Introduction Physics Motivation Experiment Setup

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S pin A symmetries of the N ucleon E xperiment

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  1. Proton Form Factor Ratio, GPE/GPM From Double Spin Asymmetries Spin Asymmetries of the Nucleon Experiment ( E07-003) Analysis Updates Anusha Liyanage Hall C User Meeting (January 25, 2013)

  2. Outline • Introduction • Physics Motivation • Experiment Setup • Polarized Target • Elastic Kinematic • Data Analysis & MC/SIMC Simulation • Conclusion

  3. IntroductionNucleon Elastic Form Factors • Defined in context of single-photon exchange. • Describe how much the nucleus deviates from a point like particle. • Describe the internal structure of the nucleons. • Provide the information on the spatial distribution of electric charge (by electric form • factor,GpE) and magnetic moment ( by magnetic form factor, GpM) within the proton. • Can be determined from elastic electron-proton scattering. • They are functions of the four-momentum transfer squared, Q2 The four-momentum transfer squared,

  4. General definition of the nucleon form factor is Fourier transforms of the charge, and magnetic moment, distributions in Breit Frame Sachs Form Factors ; ; F1 – non-spin flip (Dirac Form Factor) describe the charge distribution F2 – spin flip (Pauli form factor) describe the magnetic moment distribution At low At

  5. Form Factor Ratio Measurements • Rosenbluth separation method. • Measure the electron - unpolarized proton elastic scattering cross section at fixed Q2 by varying the scattering angle, θe. • Strongly sensitive to the radiative corrections. E - Incoming electron energy E/ - Outgoing electron energy θe- Outgoing electron’s scattering angle Mp- Proton mass Y = m X + C The gradient = , The Intercept = ,

  6. Polarization Transfer Technique. • Measure the recoil proton polarization components from elastic scattering of polarized electron-unpolarized proton. • Ratio insensitive to absolute polarization, analyzing power. • Less sensitive to radiative correction. E - Incoming electron energy E/ - Outgoing electron energy θe– Outgoing electron’s scattering angle MP - Proton mass Polarization along q Polarization perpendicular to q (in the scattering plane) Polarization normal to scattering plane.

  7. Double-Spin Asymmetry. • Measure the double asymmetry between even (++, --) and odd (+-, -+) combinations of electron and proton polarization. • Different systematic errors than Rosenbluth or proton recoil polarization methods. • The sensitivity to the form factor ratio is similar to that of the Polarization Transfer Technique. Here, r = GpE /GpM a, b, c = kinematic factors , = pol. and azi. Angles between and Ap = The beam - target asymmetry

  8. Physics Motivation • Dramatic discrepancy between • Rosenbluth and recoil polarization • technique. • Multi-photon exchange considered • the best candidate for the • explanation • Double-Spin Asymmetry • is an independent • technique to verify • the discrepancy RSS (Jlab) Q2 = 1.50 (GeV/c)2 Dramatic discrepancy ! SANE 2.06 5.17 6.25 Q2 (GeV/c)2

  9. Experiment Setup • BETA for coincidence electron • detection • Central scattering angle: 40 ° • Over 200 msr solid angle • coverage Hall C at Jefferson Lab • HMS for scattered • proton or electron • detection • Central angles are • 22.3° and 22.0° • Solid angle ~10 msr Elastic (e , e’p) scattering from a polarized NH3 target using a longitudinally polarized electron beam (Data collected from Jan – March, 2009)

  10. Polarized Target The Polarized Target Assembly • C, CH2 and NH3 • Dynamic Nuclear Polarization (DNP) polarized the protons in the NH3 target up to 90% at 1 K Temperature 5 T Magnetic Field • Temperature is maintained by immersing the entire target • in a liquid He bath • Used microwavesto excite spin flip transitions (55 GHz - 165 GHz) • Polarization measured using NMR coils • To maintain reasonable target • polarization, the beam current • was limited to 100 nA and • uniformly rastered.

  11. Polarized Target Magnetic Field ( 80 and 180 deg ) ΘB = 80° • Used only perpendicular magnetic field configuration for the elastic data • Average target polarization is ~ 70 % • Average beam polarization is ~ 73 % ΘB = 180°

  12. Elastic Kinematics ( From HMS Spectrometer )

  13. Data Analysis Electrons in HMS By knowing, theincoming beam energy, , scattered electron energy, and the scattered electron angle, Θ E e- p e- p E’

  14. Momentum Acceptance P -Measured momentum in HMS Pc-HMS central momentum The elastic data are outside of the usual delta cut +/- 8% hsdelta (%) Use -8% < <10% & Invariant Mass, W (GeV/c2) Use 10% < <12%

  15. Extract the electrons • Used only Electron selection cuts. # of Cerenkov photoelectrons > 2 - Cerenkov cut > 0.7 - Calorimeter cut -8% < < 10% and 10% < <12% - HMS Momentum Acceptance cuts Here, - Total measured shower energy of a chosen electron track by HMS Calorimeter - Detected electron momentum/ energy at HMS - Relative momentum deviation from the HMS central momentum -8% < < 10% 10% < < 12%

  16. Extracted the Asymmetries ….. The raw asymmetry, Ar N+ / N- = Charge and live time normalized countsfor the +/- helicities ∆Ar = Error on the raw asymmetry -8% < < 10% 10% < <12%

  17. Extracted the Asymmetries ….. Need dilution factor, f in order to determine the physics asymmetry, and GpE/GpM (at Q2=2.2 (GeV/c)2 ) PBPT = Beam and target polarization Nc = A correction term to eliminate the contribution from quasi-elastic scattering on polarized 14N under the elastic peak (negligible in SANE) Use MC/DATA comparison for NH3 target to extract the dilution factor…..

  18. MC for C run Srast x offset=-0.4 cm Srast y offset=0.1 cm

  19. MC with NH3 • Generated N, H and He separately. • Added Al coming from target end caps and 4K shields as well. • Calculated the MC scale factor using the data/MC luminosity • ratio for each target type. • Added all targets together by weighting the above MC scale factors. • Used 60% packing fraction. • Adjusted acceptance edges in Y and Y’ by adjusting the horizontal beam position. • Adjusted the vertical beam position to bring the elastic peak to GeV. srastx= -0.40 cm srasty= 0.10 cm

  20. Determination of the Dilution Factor What is the Dilution Factor ? -8% < < 10% The dilution factor is the ratio of the yield from scattering off free protons(protons from H in NH3) to that from the entire target (protons from N, H, He and Al) Each target type contributions (Top target) Dilution Factor, Invariant Mass, W (GeV/c2) Invariant Mass, W (GeV/c2)

  21. MC Background contributions (Only He+N+Al) • Calculate the ratio of • YieldData/YieldMC for the • region 0.7 < W <0.85 • and MC is normalized • with this new scaling factor. • Used the polynomial fit • to N+ He+Al in MC • and • Subtract the fit function • from data Invariant Mass, W (GeV/c2)

  22. 10% < < 12% Each target type contributions (Top target) Invariant Mass, W (GeV/c2) Invariant Mass, W (GeV/c2) Invariant Mass, W (GeV/c2)

  23. The relative Dilution Factor The relative dilution factor for two different targets, top and bottom for two different delta regions, Dilution Factor, -8% < < 10% and 10% < <12% • We have taken data using both NH3 targets, called NH3 top and NH3 bottom. • NH3 crystals are not uniformly filled in each targets which arise two different packing fractions and hence two different dilution factors. Invariant Mass, W (GeV/c2)

  24. Beam /Target Polarizations COIN data Single arm electron data

  25. The Physics Asymmetry 10% < < 12% -8% < < 10% Phys. Asym., AP Phys. Asym., AP Invariant Mass, W (GeV/c2) Invariant Mass, W (GeV/c2)

  26. The beam - target asymmetry, Ap Here, r = GE /GM a, b, c = kinematic factors , = pol. and azi. Angles between and • Error propagation from the experiment From the HMS kinematics, r2 << c Where ,μ – Magnetic Moment of the Proton=2.79

  27. Preliminary …..

  28. Coincidence Data • (Electrons in BETA and Protons in HMS) Definitions : Yclust • X/Yclust - Measured X/Y positions on • the BigCal • X = horizontal / in-plane coordinate • Y = vertical / out – of – plane • coordinate • Eclust - Measured electron energy at the • BigCal Xclust e’ P ΘP e By knowing the energy of the polarized electron beam, EB and the scattered proton angle,ΘP • We can predict the • X/Y coordinates - X_HMS, Y_HMS and • ( Target Magnetic Field Corrected) • The Energy - E_HMS • of the coincidence electron on the BigCal

  29. Elastic Kinematics ( From HMS Spectrometer )

  30. Fractional momentum difference Data MC PHMS – Measured proton momentum by HMS Pcal - Calculated proton momentum by knowing the beam energy, E and the proton angle,Θ Pcent – HMS central momentum

  31. X/Y position difference X position difference Data MC Y position difference X_HMS-Xclust/ cm Y_HMS-Yclust/ cm

  32. Applied the coincidence cuts abs(X_HMS-Xclust)<7 Y_HMS-Yclust/ cm X_HMS-Xclust/ cm Abs( )<0.02 abs(Y_HMS-Yclust)<10

  33. Elastic Events 4.72 GeV data 5.89 GeV data Y_HMS-Yclust/ cm Y_HMS-Yclust/ cm X_HMS-Xclus/ cmt X_HMS-Xclus/ cmt Raw # of Yields Raw # of Yields Run Number Run Number

  34. Extract the Raw Asymmetries • Raw yields are normalized with • Total Charge • charge average +/- life times Need dilution factor, f in order to determine the physics asymmetry, and GpE/GpM

  35. Determine The Dilution Factor • Estimate The Background • Get the ratio of data/SIMC_C for the region of 0.03 < < 0.08. (ratio=2.73893) • Normalized the SIMC_C with that ratio (2.73893) for the region of -0.1 < < 0.1 and added SIMC_H3 to it. Compare with the data. • Data/SIMC(H3+2.73893*C) = 0.991536 • Used the Gaussian fit for the SIMC_C (normalized with 2.73893) and subtract it from the data • Get the relative dilution factor by taking the ratio of SIMC_C substracted data to data. • the relative df. = (data-SIMC_C)/data

  36. Get The Relative Dilution Factor Two different target cups (NH3 Top and NH3 Bottom) Two different packing fractions Need Two different dilution factors

  37. The Relative Dilution Factors For Top Target Bottom Target

  38. The Relative Dilution Factor • (Used the Integration Method) • Because of the low statistics, It is hard to correct the raw asymmetry for the df as a function of • Just integrate over the region of +/- 0.02 for the top and bottom. Top Target Bottom Target The relative D.F = (data-SIMC_C)_top/data_top = 606-130/606 = 0.785 = (data-SIMC_C)_bot/data_bot = 541-92/541 = 0.830 Similarly, the relative D.F for 4.72 GeVbeam energy is 0.816

  39. Beam and Target Polarizations • Used the runs of beam polarization > 60 % and abs(target polarization) > 55 % • Used the charge average target and beam polarizations to calculate the physics asymmetries

  40. Extract the Physics Asymmetries

  41. Extract the Proton Form Factor Ratio, GpE/GpM Preliminary ….. Q2 (GeV/c)2

  42. Measurement of the beam-target asymmetry in elastic electron-proton scattering offers an independent technique of determining the GpE/GpMratio. • This is an ‘exploratory’ measurement, as a by-product of the SANE experiment. • Extraction of the GpE/GpMratio from single-arm electron and coincidence data are shown. • The preliminary data point at Q2=2.06 (GeV/c)2is very consistent with the recoil polarization data. • The preliminary weighted average data point of the coincidence data at Q2=5.72 (GeV/c)2 has large error due to the lack of elastic events. Conclusion

  43. SANE Collaborators: Argonne National Laboratory, Christopher Newport U., Florida International U., Hampton U., Thomas Jefferson National Accelerator Facility, Mississippi State U., North Carolina A&T State U., Norfolk S. U., Ohio U., Institute for High Energy Physics, U. of Regina, Rensselaer Polytechnic I., Rutgers U., Seoul National U., State University at New Orleans , Temple U., Tohoku U., U. of New Hampshire, U. of Virginia, College of William and Mary, Xavier University of Louisiana, Yerevan Physics Inst. Spokespersons: S. Choi (Seoul), M. Jones (TJNAF), Z-E. Meziani (Temple), O. A. Rondon (UVA) Thank You

  44. Packing Fraction. • Packing fraction is the actual amount of target material normalized the nominal amount expected for the target volume. • Determined by taking the ratio of data to MC as a function of W. • Need to determine the packing fractions for each of the NH3 loads used during the data taking. Hoyoung Kang’s work

  45. Determine the Packing Fraction Consistent with Hoyoungkang’s packing fraction determinations !!!! • Compared data to SIMC simulation for the NH3 target for 3 different Packing Fractions. • Normalized MC_NH3 by 0.93 which is the factor that brings C data/MC ratio to 1. • Determined the packing fraction which brings Data/MC ratio to 1 from the plot. • Packing Fraction=56.3 %

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