1. 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

2. Principle + 2 g(Q2) e- N e- X =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
David Lhuillier , CEA Saclay

3. A Bit of History: E122 @ SLACg e 2H X
,Z0 e’
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
David Lhuillier , CEA Saclay

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)
David Lhuillier , CEA Saclay

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
David Lhuillier , CEA Saclay

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

7. Elastic Scattering + 2 g(Q2) e- N e- N = GFQ2Z0 + e’
e- N e- N = 2
Electromagnetic FF
Weak FF
ALR= f(F1g,F2g,F1Z,F2Z,GA)
GFQ2
2pa 2
few ppm
at Q2<1 (GeV/c)2
David Lhuillier , CEA Saclay

8. Strange content of the Nucleon
Sum over 3 quarks flavours (u,d,s)
weighted by elec. and weak charges
Charge symmetry
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>
Extraction of the strange quarks contribution
3x3 equations
Same relations
stand for GE/GM…
David Lhuillier , CEA Saclay

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

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

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
Jlab
Q2= (Gev/c)2
MAMI
Q2=0.1 and 0.25 (Gev/c)2
but not enough lever arm to extract the 3 contributions
David Lhuillier , CEA Saclay

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
David Lhuillier , CEA Saclay

13. Experimental Program Q2 dependence First moments
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 ~ fm2 ~ <rn2>Sachs/6
David Lhuillier , CEA Saclay

14. Weak Charged Current in e-p scatteringZ0
The NEPTUNE experiment n e- W-
Letter Of Intent at JLab (A. Deur)
High luminosity
Direct measurement + p n -
Only detected particle = n
GE,M V GA GP
David Lhuillier , CEA Saclay

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

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

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

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
David Lhuillier , CEA Saclay

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
David Lhuillier , CEA Saclay

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
David Lhuillier , CEA Saclay