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Weak probe of the nucleon in electron scattering

Weak probe of the nucleon in electron scattering. Weak Current far from the Z pole History Elastic Scattering and strange content of the nucleon Perspectives in charged current and DIS kinematics Conclusion. e - N e - X =. Principle. 2. e ’. e ’. e. e. g (Q 2 ).

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Weak probe of the nucleon in electron scattering

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  1. Weak probe of the nucleonin electron scattering • Weak Current far from • the Z pole • History • Elastic Scattering and strange • content of the nucleon • Perspectives in charged • current and DIS kinematics • Conclusion

  2. e- N e- X= Principle 2 e’ e’ e e g(Q2) + Z0 N X N X Nice perturbative probe Q2 << MZ2 at typical “hadronic scale” But weak interaction violates P  Build a pseudo-scalar observable, prop. to MZ: ALR~GFQ2/4pa ALR~10-4 at Q2=1 (GeV/c)2

  3. e’ e g ,Z0 X 2H A Bit of History: E122 @ SLAC DIS off deuteron target: x=Q2/2Mn y=n/E • Isoscalar target: fu(x)=fd(x) • Neglect sea distributions: x > 0.2 x dependence factorizes out

  4. A bit of History: E122 @ SLAC C.Y.Prescot et al, Phys. Lett. 84B, 524 (1979) Weinberg-Salam First constraint establishing the Weinberg-Salam Model: Hybrid sin2qW= 0.224+/-0.020 • Extensions: • Low x: probe sea contribution with sin2qW as input • Larger x: precise test of sin2qW • (Jlab LOI, complementary to E158 and Qweak)

  5. Parity Violation in e- Scattering Test SM Elastic e--N Factor 1000 ! • Mutual enrichment between test of SM and hadronic structure • Impressive performances of polarized beam

  6. l/2 Charge asymmetry at 1 GeV Half-wave plate reversals IN OUT Final: AI=-8.4+/-7.8 ppb (10-9) ! Experimental Techniques Injector Beam line Hall Key elements: Source • High Pe and I • Rapid helicity flip • Feedbacks “Table-Top” Experiments

  7. 2 e’ e’ e e g(Q2) + Z0 N N N N e- N e- N= GFQ2 2pa 2 ALR= f(F1g,F2g,F1Z,F2Z,GA) Elastic Scattering Electromagnetic FF Weak FF few ppm at Q2<1 (GeV/c)2

  8. Charge symmetry Extraction of the strange quarks contribution Same relations stand for GE/GM… 3x3equations Motivation triggered by DIS results on Ds but the measured matrix elements are independent: vector <N|sgms|N>instead of pseudo-vector <N|sgmg5s|N> Strange content of the Nucleon Sum over 3 quarks flavours (u,d,s) weighted by elec. and weak charges

  9. <rs2>Sachs (fm2) Leading Non Zero Moments Measurements at low Q2 • Strange Charge Radius: Scale: <r2n>Sachs=0.12 fm2 • Strange Magnetic Moment: Scale: mN

  10. ms= -0.3 <rs2>Sachs= 0.33 fm2 Elastic e-p Asymmetry Forward angle: GsE,GsM Backward angle: GsM,GA

  11. Experimental Strategy Complete Separation GE/GM/GA over Q2=0.11 (GeV/c)2 Rosenbluth Method Forward and backward measurements with the same detector setup G0 @ Jlab Q2=0.3-0.8 (Gev/c)2 PVA4 @ MAMI Q2=0.1 and 0.25 (Gev/c)2 but not enough lever arm to extract the 3 contributions

  12. Experimental Strategy Complete Separation GE/GM/GA over Q2=0.11 (GeV/c)2 Different targets Quasi-elastic e-Deuteron Elastic e-4He: Isoscalaire Transition pure GE SAMPLE MIT-Bates HAPPEx2 JLab Q2=0.1 GeV/c2

  13. Experimental Program Q2 dependence G0, PVA4, HAPPEx1 0.2 < Q2 < 0.8 (GeV/c)2 First moments SAMPLE, HAPPEx2, PVA4 Q2 = 0.1 (GeV/c)2 • First Constraint on ms: ms=0.37+/-0.20stat+/-0.26syst+/-0.15theo • Expected combined accuracy: dms ~ 0.16 mN d<rs2>Sachs ~ 0.020 fm2 ~ <rn2>Sachs/6

  14. Z0 W- W+ V GE,M GA GP Weak Charged Current in e-p scattering The NEPTUNE experiment n e- W- Letter Of Intentat JLab (A. Deur) • High luminosity • Direct measurement + p n - • Only detected particle = n

  15. e- NEPTUNE Experimental Setup • Background reduction: • Backward kinematic • Sweepnig magnet • Recoil detector • Pulsed beam S/B~0.1 • APV=10% • Accurate normalization despite bad S/B. Symmetric w.r.t. beam axis (not represented)

  16. NEPTUNE Projected Results n e-pnn p electroproduction GA E=1-2 GeV qe=120deg Q2=0.8-2.7 Q2 (GeV/c)2 • Accurate data in an unexplored kinematical domain of a fundamental observable of the nucleon

  17. e’ e+,e- g ,Z0 X p Parity Violating Asymmetry in e-p DIS Extract G3 separate valence and sea contributions …

  18. Parity Violating Asymmetry in e-p DIS • Single spin asymmetry: • G3 term is suppressed • but ratio G2/F2 depends on d/u • ALR ~ 10-5 Q2, allows accurate • measurements • Charge asymmetry: • First data from HERA, • Stat. Limited • Intense neutrino beams [se+-se-] a xG3

  19. Conclusion Weak Neutral Current in e- scattering: • New probe of the nucleon structure • Important experimental program ongoing to extract • the contribution of strange quarks to the vector • matrix element <N|sgms|N>. Development of experimental techniques • Perspectives in charged current (GA) and DIS neutral current (d/u). • Precise test of the interaction itself

  20. Back to the Future • New results from ALR in Moller scattering from E158 at SLAC. • Parity violating asymmetries allow precise test of SM at low energy

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