Strangeness in the Nucleon Newest Results from HAPPEx and G0

1. Strangeness in the NucleonNewest Results from HAPPEx and G0 • Physics case • Electroweak Standard Model • Experimental Aspects • Results and Perspectives D. Lhuillier - CEA Saclay

2. Physics Case • Nucleon Structure: • Valence quarks dressed by gluon exchange and qq fluctuations. • Quark sea, key component on the nucleon. • Strangeness in the nucleon: s quark flavor decouples from valence quarks but may still be light enough to contribute. “Low Q” physics D. Lhuillier - CEA Saclay

3. Strange Quarks in the Nucleon Strange sea measured in N scattering Strange sea is well-known, but contributions to nucleon matrix elements are somewhat unsettled: • Spinpolarized DIS • Inclusive: Ds = -0.08 ± 0.05 • Semi-inclusive: Ds = 0.03± 0.03 • Strange mass • pN scattering: 0-30% • Strange vector Form Factor D. Lhuillier - CEA Saclay

4. Form Factors Elastic scattering off a static potential (no spin): (q) • Direct image of the charge distribution inside the target, in the limit of no recoil (Q2<M2). D. Lhuillier - CEA Saclay

5. FT Electromagnetic Form Factors Nucleon target: 2S+1 form factors e- Charge (q) Magnetization p,n D. Lhuillier - CEA Saclay

6. e- (q) Charge symmetry u-d Flavour Separation s quarks distributions? GEs(0) = 0, no other symmetry constraints… D. Lhuillier - CEA Saclay

7. Z0 new probe of the nucleon, only assumes charge sym. • Sensitive to (s - s ). Weak Form Factors e- Vector Axial Z0 (q) • 3 flavors separation: D. Lhuillier - CEA Saclay

8. 180 deg. • Electromagnetism • Gravitation • Strong interaction • Weak interaction Parité (Réflexion / O) O Sym. miroir g g g g g g Vector : Pseudo-vector: Scalar : Pseudo-scalar : r,p,E s=rLp,B m h=s.p -r,-p,-E +s,+B +m -h g g g g g g g g Parity Symmetry D. Lhuillier - CEA Saclay

9. T.D.Lee/C.N.Yang Measure a Pseudoscalar… Propose to test PV in weak interactions C.S. Wu • decay of polarized 60Co M. Gell-Mann/R. Feynman (V-A) theory Lee & Yang M. Goldhaber Left handed neutrino 1957 ! D. Lhuillier - CEA Saclay

10. (CERN, 1973) f Partial P in neutral weak current  electroweak unification. Z0 e± JZ0 = J3 – sin2qW Jem J+, J-, …. J3 SU(2)LxU(1)Y W± W+, W-, …. Z0  f cfV = T3 – 2sin2qWQf cfA = T3 (V-A) Electroweak Standard Model • Weak isospin group SU(2)L: D. Lhuillier - CEA Saclay

11. -Z0 Interference 2 e- e- (Q) Z0 (Q) +  = |MgMZ|2 = Scale ~ 1 fm MZ ~ Q2 <<MZ2 << Mg~ Z0 contribution in the cross section is negligible… D. Lhuillier - CEA Saclay

12. Parity Violating Asymmetry Lee & Yang:measure a pseudoscalar quantity APV, generated by helivcity flip of the e- beam NL NR D. Lhuillier - CEA Saclay

13. E122@SLAC b e- e- PVDIS 2H X a Isoscalar target: aand b ~ cst (@ large x) C.Y. Prescott et al., 1978 APV~10-4 ±10-5 sin2qW = 0.224 ± 0.020 D. Lhuillier - CEA Saclay

14. Backward angle Forward angle 4He target:GEs alone 2H target: enhanced GAe sensitivity Weak Form Factors Proton target: ~ few parts per million D. Lhuillier - CEA Saclay

15. Experimental Strategies G0 : Large , Particle id, large Q2 range HAPPEx : small , integrating, single accurate Q2 D. Lhuillier - CEA Saclay

16. Experimental Challenges Goal: down to ~50 ppb absolute error and 2% relative • High rate • High beam polarization • Control of beam asymmetries • Background rejection • Normalization D. Lhuillier - CEA Saclay

17. « Table Top » Experiments DAQ • No “external” instrumentation: • Control of the polarized source • Redundant beam monitoring from injector to experimental hall D. Lhuillier - CEA Saclay

18. The Polarized e- Source • Optical pumping of strained GaAs cathode produces highly-polarized e- beam. • “Strain” boosts polarization but introduces anisotropy in response. • Rapide and pseudo-random helicity flip. • Pair asymmetry measured several million times to reach stat. error. D. Lhuillier - CEA Saclay

19. Beam Asymmetries Intensity: Beam Axis Position: Typical sensitivity: 10ppm/m • Azimuthally symmetric detector • Most h.c. beam asymmetries trace back to differences in preparation of circularly polarized laser light at the source. X=XR-XL D. Lhuillier - CEA Saclay

20. PITA Effet Polarization Induced Transport Asymmetry Perfect ±l/4 retardation leads to perfect D.o.C.P. • Now L/R states have opposite sign linear components. • This couples to “asymmetric transport” in the optics system to produce an intensity asymmetry. Acommonretardation offset over-rotates one state, under-rotates the other Right helicity Left helicity This is theD phase D. Lhuillier - CEA Saclay

21. Intensity Asymmetry using RHWP minimum analyzing power maximum analyzing power A rotatable l/2 plate downstream of the P.C. allows arbitrary orientation of DoLP Electron beam intensity asymmetry (ppm) 4q term measures Ana Power*DoLP (from Pockels cell) Rotating waveplate angle D. Lhuillier - CEA Saclay

22. OpticsTable High Pe High Q.E. Low Apower Strategy • Rapid, pseudo-random helicity flip. • Careful config. to reduce beam asym. • Feedback systems to zero residual asym. measured in exp. hall. • Further cancellation by slow helicity reversals. controls effective analyzing power Tune residual linear pol. Slow helicity reversal Intensity Attenuator (charge Feedback) D. Lhuillier - CEA Saclay

23. Feedback Reduce remaining effects Position (G0) charge Performances: Figures from K.Nakahara AI < 1 ppm x ~ 1 nm 10 ppb final correction Cates et al., NIM A vol. 278, p. 293 (1989) T.B. Humensky et. al., NIM A 521, 261 (2004) D. Lhuillier - CEA Saclay

24. Asymmetry (ppm) Slug Slow Reversals Pure statistical distribution of the pair asymmetries Helicity Window Pair Asymmetry Sign flip of APV under insertion / removal of the half-wave plate at the source D. Lhuillier - CEA Saclay

25. Polarimeters Compton 1% syst Continuous Møller 2% syst JLab Hall A E~3GeV, =6° Q2~0.1 GeV/c2 Target 400 W transverse flow 20 cm, LH2 20 cm, 200 psi 4He High Resolution Spectrometer S+QQDQ 5 mstr over 4o-8o D. Lhuillier - CEA Saclay

26. PMT Elastic Rate: 1H: 120 MHz Cherenkov cones 4He: 12 MHz PMT Overlap the elastic line above the focal plane and integrate the flux Very clean separation of elastic events by HRS optics  Happex Detectors 100 x 600 mm ADC 12 m dispersion sweeps away inelastic events Large dispersion and heavy shielding reduce backgrounds at the focal plane D. Lhuillier - CEA Saclay

27. JLab Hall C Detector wheel G0 beam monitoring girder Superconducting magnet D. Lhuillier - CEA Saclay

28. Forward angle configuration G0 Detectors protons Q2=0.1-1.0 GeV/c2 Detectors Magnet elastic protons Inelastic protons Beam + Target ToF histogram D. Lhuillier - CEA Saclay

29. CED+ Cherenkov FPD Backward angle configuration e- beam target G0 Detectors electrons e~110° Magnet Beam Target D. Lhuillier - CEA Saclay

30. Polarimetry Main normalization error, Aexp = Pe.APV - Moller polarimetry in hall C: solid target saturated in high B field 1.3% relative accuracy Interleaved runs at low current - Compton polarimetry in hall A: continuous monitoring FOM strongly depends on Ebeam 1.0% relative accuracy @ 3GeV D. Lhuillier - CEA Saclay

31. Results @ Q2=0.1 GeV/c2 HAPPEX only : APVh=-1.58± 0.12 ± 0.04 ppm APVHe=6.40 ± 0.23 ± 0.12 ppm GMs = 0.18 ± 0.27 GEs = -0.005 ± 0.019 Global fit: GMs = 0.22 ± 0.20 GEs = -0.011 ± 0.016 <6% de p, <5% rs (95% CL) R.D.Young, et al, hep-ph/0704.2618 D. Lhuillier - CEA Saclay

32. Results @ Q2=0.1 GeV/c2 16. Skyrme Model - N.W. Park and H. Weigel, Nucl. Phys. A 451, 453 (1992). 17. Dispersion Relation - H.W. Hammer, U.G. Meissner, D. Drechsel, Phys. Lett. B 367, 323 (1996). 18. Dispersion Relation - H.-W. Hammer and Ramsey-Musolf, Phys. Rev. C 60, 045204 (1999). 19. Chiral Quark Soliton Model - A. Sliva et al., Phys. Rev. D 65, 014015 (2001). 20. Perturbative Chiral Quark Model - V. Lyubovitskij et al., Phys. Rev. C 66, 055204 (2002). 21. Lattice - R. Lewis et al., Phys. Rev. D 67, 013003 (2003). 22. Lattice + charge symmetry -Leinweber et al, Phys. Rev. Lett. 94, 212001 (2005) & hep-lat/0601025 D. Lhuillier - CEA Saclay

33. Q2 Dependence Proton Data • Small strange quarks contribution at low Q2 • G0 and PVA4 backward results to be released soon • Happex-III likely to run in 2009 D. Lhuillier - CEA Saclay

34. Projected G0 Results D. Lhuillier - CEA Saclay

35. Perspectives PRex: APV in elastic e--208Pb scattering (JLab Hall A) Goal: dRn/Rn~1% • Z0 couples mainly to neutrons: • --> new accurate measurement independent of nuclear models, pins down sym. energy • --> Constraint on neutron stars structure C.J. Horowitz, Phys. Rev. C 64, 062802 (2001) D. Lhuillier - CEA Saclay

36. Perspectives Test of the Standard Model at Low Energy Combining global fit and extrapolation to Q2=0 sets new limits on C1q and constrains new physics at the TeV scale: Qweak @ JLab --> Further improvement by a factor 5 PV-DIS @ JLab • Constraint the C2q axial couplings using isoscalar target • New generation E122 exp. @ JLab R.D.Young, et al, hep-ph/0704.2618 D. Lhuillier - CEA Saclay

37. MollerJlab Qweak Running of sin2w E158 LEP-SLC k(0)=1.03 sin2eff (E158) = 0.2397 ± 0.0013 D. Lhuillier - CEA Saclay

38. Summary • Tremendous progress in experimental techniques over last 10 years • Study of the strange nucleon form factors almost completed. Stringent upper limits already set at low Q2. • Weak neutral current at low energy established as a new probe of the nucleon … and the weak interaction itself. • Perspectives at the crossing of nuclear, particle and astro physics with PRex and test of SM at low energy. D. Lhuillier - CEA Saclay