1. May 17, 2006Sebastian Baunack, PAVI06 The Parity Violation A4 Experiment at forward and backward angles Strange Form Factors The Mainz A4 Experiment Result at forward angles A look at backward angles Sebastian Baunack for the A4 collaboration

2. May 17, 2006Sebastian Baunack, PAVI06 Structure of the Nucleon Contribution of s-quarks to the vector current Constituent QuarksQCD: sea quarks, gluons… e-e- e-e-  Z0Z0 p Electromagnetic interaction Weak interaction

3. May 17, 2006Sebastian Baunack, PAVI06 PV Asymmetry Weak interaction: Parity violation Flavour Decomposition of form factors: Universality of quark distribution, charge symmetry…

4. May 17, 2006Sebastian Baunack, PAVI06 Extraction of Strange FF : No strangeness Strangeness contribution Strange FF extractable! Standard model calculation

5. May 17, 2006Sebastian Baunack, PAVI06 A4 Kinematics p-Target 35 º Detector rotated Forward angles: sensitive to with  Q 2 [in GeV/c) 2 ] E=854.3 MeV Q 2 = 0.23 (GeV/c) 2 A 0 = -6.30 ppm E=570.4 MeV Q 2 = 0.11 (GeV/c) 2 A 0 = -2.08 ppm e-e-

6. May 17, 2006Sebastian Baunack, PAVI06 A4 Kinematics p-Target 145 º Detector rotated Backward angles: sensitive to (and the axial term) E=315.1 MeV Q 2 = 0.23 (GeV/c) 2 A 0 = -16.2 ppm (A V =-13.6 ppm, A A =-2.6 ppm) e-e-

7. May 17, 2006Sebastian Baunack, PAVI06 Statistics with Count elastic events N +, N - 5% Accuracy: Q 2 = 0.11 (GeV/c) 2 forward : N total =1 x 10 14 Q 2 = 0.23 (GeV/c) 2 forward : N total =1 x 10 13 Q 2 = 0.23 (GeV/c) 2 backward: N total =1 x 10 12 A4: Large solid angle (0.6 sr) PbF 2 calorimeter Meas. Time 1100 h 400 h 600 h

8. May 17, 2006Sebastian Baunack, PAVI06 A4 Experiment at MAMI Forward angle configuration Polarized GaAs electron source I=20  A, P=80% MAMI E=854.3 MeV E=570.4 MeV Compton Laser Backscatter Polarimeter 10 cm liquid hydrogen target PbF 2 Calorimeter Luminosity monitors Transmisson Compton Polarimeter

9. May 17, 2006Sebastian Baunack, PAVI06 A4 Experiment at MAMI Backward angle configuration Polarized GaAs electron source I=20  A, P=80% MAMI E=854.3 MeV E=570.4 MeV Compton Laser Backscatter Polarimeter 20 cm liquid hydrogen target PbF 2 Calorimeter Luminosity monitors Transmisson Compton Polarimeter Scintillator

10. May 17, 2006Sebastian Baunack, PAVI06 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

11. May 17, 2006Sebastian Baunack, PAVI06 Compton Backscatter Polarimeter => J. Diefenbach, May 20, 16:30

12. May 17, 2006Sebastian Baunack, PAVI06 PbF 2 Calorimeter 1022 PbF 2 crystals in 7 rings and 146 frames Pure Cerenkov radiator, intrinsically fast Solid angle:  =0.6 sr,    or  Total rate  MHz Sum of 3x3 crystals

13. May 17, 2006Sebastian Baunack, PAVI06 Luminosity monitors 8 Integrating water Cerenkov detectors Measurements every 20ms Small forward angles, 4.4 °  10°, optimized for Moller electrons

14. May 17, 2006Sebastian Baunack, PAVI06 Transmission Compton Polarimeter (TCP) Relative measurement of polarization Determination of electron spin angle Control of halfwave plate status Asymmetry/10 -5

15. May 17, 2006Sebastian Baunack, PAVI06 Forward angle measurements PbF 2 Energy spectrum Single channel,  =34.1 ° E=854.3 MeV Q 2 =0.23 (GeV/c) 2 I = 20  A, t = 2.5min Fit: Double Gaussian plus exponential Calc. energy resolution

16. May 17, 2006Sebastian Baunack, PAVI06 Forward angle measurements Calculate low ADC cut: From fit Can be choosen, We use k=1.6 High ADC cut: No difficulty Elastic events N +, N -

17. May 17, 2006Sebastian Baunack, PAVI06 Forward angle measurements PbF 2 Energy spectrum Single channel,  =34.1 ° E = 570.4 MeV Q 2 = 0.11 (GeV/c) 2 I = 20  A, t = 2.5min Also clean extraction of elastic events

18. May 17, 2006Sebastian Baunack, PAVI06 Analysis For each 5min run: 2044 spectra (+/-)

19. May 17, 2006Sebastian Baunack, PAVI06 Analysis Experimental Asymmetry: with  target density Elastic events for one run: P: Beam polarisation X 1 : Current asymmetry X 2 : Horiz. position diff. X 3 : Verti. Position diff. X 4 : Horiz. angle diff. X 5 : Verti. angle diff. X 6 : Energy diff. Determination of a i via multiple linear regression

20. May 17, 2006 A4 @ MAMI, forward angle Q 2 = 0.23 (GeV/c) 2 A PV =(-5.44±0.54 stat ±0.26 syst ) ppm Q 2 = 0.11 (GeV/c) 2 A PV =(-1.36± 0.29 stat ±0.13 syst ) ppm F.E. Maas et al., Phys.Rev.Lett.93:022002 (2004) F.E. Maas et al., Phys.Rev.Lett.94:152001 (2005)

21. May 17, 2006Sebastian Baunack, PAVI06 To the backward measurements p-Target 145 º Detector e-e- p-Target 35 º e-e- Detector => B. Gläser, May 17, 18:30

22. May 17, 2006Sebastian Baunack, PAVI06 PbF2 spectrum PbF 2 Energy spectrum Single channel,  =145.9 ° E=315.1 MeV Q 2 =0.23 (GeV/c) 2 I = 20  A, t = 2.5min Coincidence spectrum Backward angle

23. May 17, 2006Sebastian Baunack, PAVI06 Backward angle PbF 2 Energy spectrum Single channel,  =145.9 ° E=315.1 MeV Q 2 =0.23 (GeV/c) 2 I = 20  A, t = 2.5min PbF2 spectrum Coincidence spectrum A4 Standard fit possible Elastic events extractable

24. May 17, 2006Sebastian Baunack, PAVI06 N + back, N - back : Background analysis Backward angle N + coinc, N - coinc : used for the preliminary analysis Coincidence spectrum Noncoincidence spectrum

25. May 17, 2006Sebastian Baunack, PAVI06 Background subtraction In development Estimate background dilution factor  Subtract background: Coinc sub (ADC)=Coinc(ADC)-  × Back(ADC)

26. May 17, 2006Sebastian Baunack, PAVI06 Background subtraction Good estimation of background dilution Coincidence spectrum Coincidence spectrum with background substracted fit possible

27. May 17, 2006Sebastian Baunack, PAVI06 Backward angle, beam parameter Beam current Asymmetry Mean: -0.31 ppm   : 4.36 ppm N: 8037 Asymmetries and differences in current, position, angle, energy: The smaller, the better

28. May 17, 2006Sebastian Baunack, PAVI06 Backward angle, beam parameter Current Asymmetry A I -0.31 ppm Horiz. position diff.  X -0.10  m Verti. position diff.  Y -0.04  m Horiz. angle diff.  X‘ -7.41 nrad Verti. angle diff.  Y‘ -3.00 nrad Energy diff.  E -0.21 eV 0.31 ppm 0.15 ppm 0.06 ppm 0.03 ppm 0.01 ppm 0.00 ppm Beam parameter False Asymmetry |A False | (Estimation)

29. May 17, 2006Sebastian Baunack, PAVI06 A look at luminosity Luminosity asymmetry vs time Luminosity asymmetry smaller than 1 ppm

30. May 17, 2006Sebastian Baunack, PAVI06 Spin angle determination 1.E=315.1 MeV 2.Rotate electron spin with Wienfilter 3.Asymmetry in TCP polarimeter sensitive to longitudinal spin  S =(1.6 ± 6) °

31. May 17, 2006Sebastian Baunack, PAVI06 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 25x10 6 so far) And so on…

32. May 17, 2006Sebastian Baunack, PAVI06 Very preliminary Q 2 =0.23 (GeV/c) 2 backward About 550h of data N elastic =1.6x10 12 A out = (-14.0 ± 1.9) ppm A in = (+17.2 ± 1.8) ppm A coinc = (-15.8 ± 1.3) ppm Coincidence data Halfwave plate sign flip observable In/Out asymmetries consistent Asymmetries have expected magnitude

33. May 17, 2006Sebastian Baunack, PAVI06 Q 2 =0.23 (GeV/c) 2 backward N background =3.1x10 12 A out =(-4.6 ± 1.4) ppm A in = (+3.2 ± 1.3) ppm A back = (-3.9 ± 0.9) ppm Noncoincidence data Bg. asmmytries by a factor of 4 smaller than coinc. asymmetries Very preliminary

34. May 17, 2006Sebastian Baunack, PAVI06 Q 2 =0.23 (GeV/c) 2 backward Some speculation: A coinc = (-15.8 ± 1.3) ppm A back = (-3.9 ± 0.9) ppm Assume dilution factor  =0.1 A PV = (-17.1 ± 1.4) ppm No strangeness: A 0 =-16.2 ppm => Not very strange…… But: Analysis very preliminary!!

35. May 17, 2006Sebastian Baunack, PAVI06 Summary and Outlook PVA4 setup successfully rearranged for backward measurements 550 hours of backward data taken at Q 2 =0.23 (GeV/c) 2 First results look reasonable Analysis in ongoing Measurements at Q 2 =0.23 (GeV/c) 2 will continue soon (June 2006)