weak probe of the nucleon in electron scattering
DESCRIPTION
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 ). - PowerPoint PPT PresentationTRANSCRIPT
David Lhuillier , CEA Saclay
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
David Lhuillier , CEA Saclay
Principle
(Q2)
e
N X
Z0
e
N X
+
e’ e’
e- N e- X =
2
Nice perturbative probeQ2 << MZ
2 at typical “hadronic scale”
But weak interaction violates P
Build a pseudo-scalar observable, prop. to MZ:
ALR~GFQ2/4
ALR~10-4 at Q2=1 (GeV/c)2
David Lhuillier , CEA Saclay
A Bit of History: E122 @ SLAC
e
2HX
,Z0
e’
DIS off deuteron target:x=Q2/2M
y=/E
•Isoscalar target: fu(x)=fd(x)•Neglect sea distributions: x > 0.2
x dependence factorizes out
David Lhuillier , CEA Saclay
A bit of History: E122 @ SLAC
First constraint establishing the Weinberg-Salam Model:
Extensions:•Low x: probe sea contribution with sin2W as input•Larger x: precise test of sin2W (Jlab LOI, complementary to E158 and Qweak)
sin2W=0.224+/-0.020
C.Y.Prescot et al,Phys. Lett. 84B, 524 (1979)
Wein
berg
-Sala
m
Hyb
rid
David Lhuillier , CEA Saclay
Mutual enrichment between test of SM and hadronic structure
Parity Violation in e- Scattering
Test SM Elastice--N
Impressive performances of polarized beam
Fact
or
10
00
!
David Lhuillier , CEA Saclay
Half-wave plate reversals
IN
OUT
/2
Charge asymmetry at 1 GeV
Final: AI=-8.4+/-7.8 ppb (10-9) !
Experimental Techniques
•High Pe and I•Rapid helicity flip•Feedbacks
Key elements:
“Table-Top” Experiments
SourceHallInjector Beam line
David Lhuillier , CEA Saclay
Elastic Scattering
Electromagnetic FF
Weak FF
(Q2)
e
N N
Z0
e
N N
+
e’ e’
e- N e- N =
2
ALR= f(F1,F2
,F1Z,F2
Z,GA)GFQ2
2 2few ppm
at Q2<1 (GeV/c)2
David Lhuillier , CEA Saclay
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 s but the measured matrix elements are independent: vector <N|ss|N> instead of pseudo-vector <N|ss|N>
Extraction of the strange quarks contribution
3x3 equations
Same relations stand for GE/GM…
David Lhuillier , CEA Saclay
Leading Non Zero Moments
Strange Charge Radius:
Strange Magnetic Moment:
Scale: <r2n>Sachs=0.12 fm2
Scale: N
<r s
2>
Sach
s (f
m2)
Measurements at low Q2
David Lhuillier , CEA Saclay
Elastic e-p Asymmetry
rs2>Sachs= 0.33 fm2
s= -0.3
Forward angle: Gs
E,GsM
Backward angle:Gs
M,GA
David Lhuillier , CEA Saclay
Experimental Strategy
Complete Separation GE/GM/GA over Q2=0.11 (GeV/c)2
Rosenbluth Method
Forward and backward measurements with the same detector setup
but not enough lever arm to extract the 3 contributions
G0 @ JlabQ2=0.3-0.8 (Gev/c)2
PVA4 @ MAMIQ2=0.1 and 0.25 (Gev/c)2
David Lhuillier , CEA Saclay
Experimental Strategy
Complete Separation GE/GM/GA over Q2=0.11 (GeV/c)2
Different targets
Isoscalaire Transition pure GE Quasi-elastic e-Deuteron Elastic e-4He:
SAMPLEMIT-Bates
Q2=0.1 GeV/c2
HAPPEx2JLab
David Lhuillier , CEA Saclay
Experimental Program
s=0.37+/-0.20stat+/-0.26syst+/-0.15theo
s ~ 0.16 N <rs2>Sachs ~ 0.020 fm2 ~ <rn
2>Sachs/6
•First Constraint on s:
•Expected combined accuracy:
Q2 dependence
First moments
SAMPLE, HAPPEx2, PVA4
G0, PVA4, HAPPEx1
0.2 < Q2 < 0.8 (GeV/c)2
Q2 = 0.1 (GeV/c)2
David Lhuillier , CEA Saclay
W-W+
Z0
Weak Charged Current in e-p scattering
W-
e-
p n
GE,MV GA
GP
•Only detected particle = n
Letter Of Intent at JLab (A. Deur)
•High luminosity•Direct measurement+
-
The NEPTUNE experiment
David Lhuillier , CEA Saclay
•Background reduction:
S/B~0.1
•APV=10%
Backward kinematicSweepnig magnetRecoil detectorPulsed beam
Accurate normalization despite bad S/B.
e-
NEPTUNE Experimental Setup
Symmetric w.r.t. beam axis(not represented)
David Lhuillier , CEA Saclay
NEPTUNE Projected Results
Accurate data in an unexplored kinematical domain of a fundamental observable of the nucleon
GA
Q2
electroproduction e-pn
E=1-2 GeVe=120deg Q2=0.8-2.7
(GeV/c)2
David Lhuillier , CEA Saclay
Parity Violating Asymmetry in e-p DIS
e+,e-
pX
,Z0
e’
Extract G3 separate valence and sea contributions …
David Lhuillier , CEA Saclay
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:
[e+-e-] xG3•First data from HERA, Stat. Limited •Intense neutrino beams
David Lhuillier , CEA Saclay
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|ss|N>.
•Perspectives in charged current (GA) and DIS neutral current (d/u).•Precise test of the interaction itself
Development of experimental techniques
David Lhuillier , CEA Saclay
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