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The Parity Violation A4 Experiment at forward and backward angles

The Parity Violation A4 Experiment at forward and backward angles. Sebastian Baunack for the A4 collaboration. Strange Form Factors The Mainz A4 Experiment Result at forward angles A look at backward angles. Structure of the Nucleon. Contribution of s-quarks to the vector current.

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The Parity Violation A4 Experiment at forward and backward angles

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  1. The Parity Violation A4 Experiment at forward and backward angles Sebastian Baunack for the A4 collaboration • Strange Form Factors • The Mainz A4 Experiment • Result at forward angles • A look at backward angles Sebastian Baunack, PAVI06

  2. Structure of the Nucleon Contribution of s-quarks to the vector current Constituent Quarks QCD: sea quarks, gluons… e- • Electromagnetic interaction • Weak interaction e- Z0 g p Sebastian Baunack, PAVI06

  3. PV Asymmetry Weak interaction: Parity violation Flavour Decomposition of form factors: • Universality of quark distribution, charge symmetry… Sebastian Baunack, PAVI06

  4. Extraction of Strange FF Strangeness contribution : No strangeness Standard model calculation Strange FF extractable! Sebastian Baunack, PAVI06

  5. A4 Kinematics Detector rotated Detector 35º e- p-Target Forward angles: sensitive to E=854.3 MeV Q2= 0.23 (GeV/c)2 A0= -6.30 ppm E=570.4 MeV Q2= 0.11 (GeV/c)2 A0= -2.08 ppm with h ~ Q2 [in GeV/c)2] Sebastian Baunack, PAVI06

  6. A4 Kinematics Detector rotated Detector 145º e- p-Target (and the axial term) Backward angles: sensitive to E=315.1 MeV Q2= 0.23 (GeV/c)2 A0= -16.2 ppm (AV=-13.6 ppm , AA=-2.6 ppm) Sebastian Baunack, PAVI06

  7. Statistics Count elastic events N+, N- with Meas. Time 1100 h 400 h 600 h Q2= 0.11 (GeV/c)2forward: Ntotal=1 x 1014 Q2= 0.23 (GeV/c)2 forward: Ntotal=1 x 1013 Q2= 0.23 (GeV/c)2 backward:Ntotal=1 x 1012 5% Accuracy: A4: Large solid angle (0.6 sr) PbF2 calorimeter Sebastian Baunack, PAVI06

  8. A4 Experiment at MAMI MAMI E=854.3 MeV E=570.4 MeV Compton Laser Backscatter Polarimeter PbF2 Calorimeter Transmisson Compton Polarimeter 10 cm liquid hydrogen target Luminosity monitors Polarized GaAs electron source I=20 mA, P=80% Forward angle configuration Sebastian Baunack, PAVI06

  9. A4 Experiment at MAMI MAMI E=854.3 MeV E=570.4 MeV Compton Laser Backscatter Polarimeter PbF2 Calorimeter Transmisson Compton Polarimeter Scintillator 20 cm liquid hydrogen target Luminosity monitors Polarized GaAs electron source I=20 mA, P=80% Backward angle configuration Sebastian Baunack, PAVI06

  10. Polarized electron source • Superlattice GaAs Photocathode • Pockels cell: Rapid helicity flip every 20 ms • Rotatable halfwave plate: Current asymmetry < 10 ppm • Insertable halfwave plate:Slow helicity reversal every 50-80 h, systematic check => K. Aulenbacher, May 20, 18:00 Sebastian Baunack, PAVI06

  11. Compton Backscatter Polarimeter => J. Diefenbach, May 20, 16:30 Sebastian Baunack, PAVI06

  12. PbF2 Calorimeter • 1022 PbF2 crystals in 7 rings and 146 frames • Pure Cerenkov radiator, intrinsically fast • Solid angle: • W=0.6 sr, 0£F£2p • 30°£Q£40°or140°£Q£150° • Total rate» 100MHz • Sum of 3x3 crystals Sebastian Baunack, PAVI06

  13. Luminosity monitors • 8 Integrating water Cerenkov detectors • Measurements every 20ms • Small forward angles, 4.4°£Q£10°,optimized for Moller electrons Sebastian Baunack, PAVI06

  14. Transmission Compton Polarimeter (TCP) • Determination of electron spin angle • Relative measurement of polarization • Control of halfwave plate status Asymmetry/10-5 Sebastian Baunack, PAVI06

  15. Forward angle measurements PbF2 Energy spectrum Single channel, Q=34.1° E=854.3 MeV Q2=0.23 (GeV/c)2 I = 20mA, t = 2.5min Fit: Double Gaussian plus exponential Calc. energy resolution Sebastian Baunack, PAVI06

  16. Forward angle measurements • Calculate low ADC cut: Can be choosen, We use k=1.6 From fit • High ADC cut: • No difficulty Elastic events N+, N- Sebastian Baunack, PAVI06

  17. Forward angle measurements PbF2 Energy spectrum Single channel, Q=34.1° E = 570.4 MeV Q2 = 0.11 (GeV/c)2 I = 20mA, t = 2.5min Also clean extraction of elastic events Sebastian Baunack, PAVI06

  18. Analysis For each 5min run: 2044 spectra (+/-) Sebastian Baunack, PAVI06

  19. Analysis • Elastic events for one run: with r target density • Experimental Asymmetry: P: Beam polarisation X1: Current asymmetry X2: Horiz. position diff. X3: Verti. Position diff. X4: Horiz. angle diff. X5: Verti. angle diff. X6: Energy diff. • Determination of ai via multiple linear regression Sebastian Baunack, PAVI06

  20. A4@MAMI, forward angle Q2= 0.23 (GeV/c)2 APV=(-5.44±0.54stat±0.26syst) ppm F.E. Maas et al., Phys.Rev.Lett.93:022002 (2004) Q2= 0.11 (GeV/c)2 APV=(-1.36± 0.29stat±0.13syst) ppm F.E. Maas et al., Phys.Rev.Lett.94:152001 (2005)

  21. Detector 35º e- p-Target Detector 145º e- To the backward measurements p-Target => B. Gläser, May 17, 18:30 Sebastian Baunack, PAVI06

  22. Backward angle PbF2 Energy spectrum Single channel, Q=145.9° E=315.1 MeV Q2=0.23 (GeV/c)2 I = 20mA, t = 2.5min PbF2 spectrum Coincidence spectrum Sebastian Baunack, PAVI06

  23. Backward angle PbF2 Energy spectrum Single channel, Q=145.9° E=315.1 MeV Q2=0.23 (GeV/c)2 I = 20mA, t = 2.5min PbF2 spectrum Coincidence spectrum • A4 Standard fit possible • Elastic events extractable Sebastian Baunack, PAVI06

  24. Backward angle Noncoincidence spectrum N+back, N-back: Background analysis N+coinc, N-coinc: used for the preliminary analysis Coincidence spectrum Sebastian Baunack, PAVI06

  25. Background subtraction • In development Estimate background dilution factor e Subtract background: Coincsub(ADC)=Coinc(ADC)-e×Back(ADC) Sebastian Baunack, PAVI06

  26. Background subtraction Coincidence spectrum • Good estimation of background dilution • fit possible Coincidence spectrum with background substracted Sebastian Baunack, PAVI06

  27. Backward angle, beam parameter Asymmetries and differences in current, position, angle, energy: The smaller, the better Beam current Asymmetry Mean: -0.31 ppm s: 4.36 ppm N: 8037 Sebastian Baunack, PAVI06

  28. Backward angle, beam parameter Beam parameter False Asymmetry |AFalse| (Estimation) 0.31 ppm Current Asymmetry AI -0.31 ppm Horiz. position diff. DX -0.10 mm Verti. position diff. DY -0.04 mm Horiz. angle diff. DX‘ -7.41 nrad Verti. angle diff. DY‘ -3.00 nrad Energy diff. DE -0.21 eV 0.15 ppm 0.06 ppm 0.03 ppm 0.01 ppm 0.00 ppm Sebastian Baunack, PAVI06

  29. A look at luminosity Luminosity asymmetry vs time Luminosity asymmetry smaller than 1 ppm Sebastian Baunack, PAVI06

  30. Spin angle determination • E=315.1 MeV • Rotate electron spin with Wienfilter • Asymmetry in TCP polarimeter sensitive to longitudinal spin • QS=(1.6±6) ° Sebastian Baunack, PAVI06

  31. Backward asymmetries • Done: • Extraction of elastic events with standard A4 method • Partly corrections of helicity correlated false asymmetries • Polarization correction (based on a preliminary analysis) • Ongoing: • Development of new fit and background subtraction • Full analysis of helicity correlated false asymmetries • Target density analysis • Systematic check of energy spectra (more than 25x106 so far) • And so on… Sebastian Baunack, PAVI06

  32. Q2=0.23 (GeV/c)2 backward Very preliminary About 550h of data Nelastic=1.6x1012 Aout = (-14.0 ± 1.9) ppm Ain = (+17.2 ±1.8) ppm Acoinc= (-15.8 ± 1.3) ppm Coincidence data • Halfwave plate sign flip observable • In/Out asymmetries consistent • Asymmetries have expected magnitude Sebastian Baunack, PAVI06

  33. Q2=0.23 (GeV/c)2 backward Very preliminary Noncoincidence data Nbackground=3.1x1012 Aout = (-4.6 ± 1.4) ppm Ain = (+3.2 ±1.3) ppm Aback= (-3.9 ± 0.9) ppm • Bg. asmmytries by a factor of 4 smaller than coinc. asymmetries Sebastian Baunack, PAVI06

  34. Q2=0.23 (GeV/c)2 backward Some speculation: Acoinc= (-15.8 ± 1.3) ppm Aback= (-3.9 ± 0.9) ppm Assume dilution factor e=0.1 APV= (-17.1 ± 1.4) ppm No strangeness: A0=-16.2 ppm => Not very strange…… But: Analysis very preliminary!! Sebastian Baunack, PAVI06

  35. Summary and Outlook • PVA4 setup successfully rearranged for backward measurements • 550 hours of backward data taken at Q2=0.23 (GeV/c)2 • First results look reasonable • Analysis in ongoing • Measurements at Q2=0.23 (GeV/c)2 will continue soon • (June 2006) Sebastian Baunack, PAVI06

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