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 David Lhuillier , CEA Saclay

Principle e’ e’ e e- N e- X e g(Q 2) = N + X Q 2 << MZ 2 at typical “hadronic scale” Z 0 N X Nice perturbative probe But weak interaction violates P Build a pseudo-scalar observable, prop. to MZ: ALR~GFQ 2/4 pa ALR~10 -4 at Q 2=1 (Ge. V/c)2 David Lhuillier , CEA Saclay 2

A Bit of History: E 122 @ SLAC DIS off deuteron target: e’ e g 2 H • Isoscalar target: fu(x)=fd(x) • Neglect sea distributions: x > 0. 2 David Lhuillier , CEA Saclay x=Q 2/2 Mn y=n/E , Z 0 X x dependence factorizes out

A bit of History: E 122 @ SLAC First constraint establishing the Weinberg-Salam Model: Hybrid W ein be rg. Sa lam C. Y. Prescot et al, Phys. Lett. 84 B, 524 (1979) sin 2 q. W= 0. 224+/-0. 020 Extensions: • Low x: probe sea contribution with sin 2 q. W as input • Larger x: precise test of sin 2 q. W (Jlab LOI, complementary to E 158 and Qweak) David Lhuillier , CEA Saclay

Factor 1000 ! Parity Violation in e- Scattering Test SM Elastic e--N §Mutual enrichment between test of SM and hadronic structure §Impressive performances of polarized beam David Lhuillier , CEA Saclay

Experimental Techniques Key elements: Injector Source • High Pe and I • Rapid helicity flip • Feedbacks Beam line Hall l/2 “Table-Top” Experiments Half-wave plate reversals IN OUT Charge asymmetry at 1 Ge. V Final: AI=-8. 4+/-7. 8 ppb (10 -9) ! David Lhuillier , CEA Saclay

Elastic Scattering e’ e e- e- N N e g(Q 2) = N e’ + N 2 Z 0 N N Electromagnetic FF Weak FF ALR= G FQ 2 f(F 1 g, F 2 g, F 1 Z, F 2 Z, GA) 2 pa 2 David Lhuillier , CEA Saclay few ppm at Q 2<1 (Ge. V/c)2

Strange content of the Nucleon Sum over 3 quarks flavours (u, d, s) weighted by elec. and weak charges Charge symmetry Extraction of the strange quarks contribution 3 x 3 equations Same relations stand for GE/GM… Motivation triggered by DIS results on Ds but the measured matrix elements are independent: vector <N|sgms|N> instead of pseudo-vector <N|sgmg 5 s|N> David Lhuillier , CEA Saclay

Leading Non Zero Moments Measurements at low Q 2 Scale: <r 2 n>Sachs=0. 12 fm 2 üStrange Magnetic Moment: Scale: m. N David Lhuillier , CEA Saclay <rs 2>Sachs (fm 2) üStrange Charge Radius:

Elastic e-p Asymmetry ms= -0. 3 <rs 2>Sachs= 0. 33 fm 2 Forward angle: Gs. E, Gs. M Backward angle: Gs. M, GA David Lhuillier , CEA Saclay

Experimental Strategy Complete Separation GE/GM/GA over Q 2=0. 1 1 (Ge. V/c)2 Rosenbluth Method Forward and backward measurements with the same detector setup G 0 @ Jlab Q 2=0. 3 -0. 8 (Gev/c)2 PVA 4 @ MAMI Q 2=0. 1 and 0. 25 (Gev/c)2 but not enough lever arm to extract the 3 contributions David Lhuillier , CEA Saclay

Experimental Strategy Complete Separation GE/GM/GA over Q 2=0. 1 1 (Ge. V/c)2 Quasi-elastic e-Deuteron Different targets Elastic e-4 He: SAMPLE MIT-Bates HAPPEx 2 JLab Q 2=0. 1 Ge. V/c 2 David Lhuillier , CEA Saclay Isoscalaire Transition pure GE

Experimental Program Q 2 dependence G 0, PVA 4, HAPPEx 1 0. 2 < Q 2 < 0. 8 (Ge. V/c)2 First moments SAMPLE, HAPPEx 2, PVA 4 Q 2 = 0. 1 (Ge. V/c)2 • First Constraint on ms: ms=0. 37+/-0. 20 stat+/-0. 26 syst+/-0. 15 theo • Expected combined accuracy: dms ~ 0. 16 m. N David Lhuillier , CEA Saclay d<rs 2>Sachs ~ 0. 020 fm 2 ~ <rn 2>Sachs/6

Weak Charged Current in e-p scattering 0 W- Z W+ The NEPTUNE experiment n e- Letter Of Intent at JLab (A. Deur) W- p n V GE, M GA GP David Lhuillier , CEA Saclay + • High luminosity • Direct measurement - • Only detected particle = n

NEPTUNE Experimental Setup • Background reduction: üBackward kinematic üSweepnig magnet üRecoil detector üPulsed beam e- S/B~0. 1 • APV=10% Symmetric w. r. t. beam axis (not represented) David Lhuillier , CEA Saclay üAccurate normalization despite bad S/B.

NEPTUNE Projected Results n e-p nn p electroproduction GA E=1 -2 Ge. V qe=120 deg Q 2=0. 8 -2. 7 Q 2 (Ge. V/c)2 Accurate data in an unexplored kinematical domain of a fundamental observable of the nucleon David Lhuillier , CEA Saclay

Parity Violating Asymmetry in e-p DIS e’ e+, e- g , Z 0 p Extract G 3 separate valence and sea contributions … David Lhuillier , CEA Saclay X

Parity Violating Asymmetry in e-p DIS üSingle spin asymmetry: • G 3 term is suppressed • but ratio G 2/F 2 depends on d/u • ALR ~ 10 -5 Q 2, allows accurate measurements üCharge asymmetry: [se+-se-] a x. G 3 David Lhuillier , CEA Saclay • First data from HERA, Stat. Limited • Intense neutrino beams

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 David Lhuillier , CEA Saclay

Back to the Future • New results from ALR in Moller scattering from E 158 at SLAC. • Parity violating asymmetries allow precise test of SM at low energy David Lhuillier , CEA Saclay