1. Parity Violation in eP Scattering at JLab
Elastic and Deep Inelastic Scattering
Thanks to everyone who helped
developed the ideas presented here
P. A. Souder
Syracuse University
April 29, 2005
PV in Electron Scattering at JLab P. A. Souder

2. PV in Electron Scattering at JLab P. A. Souder
APV Measurements
APV ~ to
0.1 to 100 ppm
Steady progress in technology
part per billion systematic control
1% normalization control
JLab now takes the lead
New results from HAPPEX
Photocathodes
Polarimetry
Targets
Diagnostics
Counting Electronics E
April 29, 2005
PV in Electron Scattering at JLab P. A. Souder

3. Weak-Electromagnetic Interference
Electron Scattering off Nucleons & Nuclei
April 29, 2005
PV in Electron Scattering at JLab P. A. Souder

4. Introduction to Elastic Sacttering
Neglecting recoil and spin:
Obtain Fourier transform of charge distribution
Nucleon charge and magnetization distributions:
GE(Q2), GM(Q2)
GEp(0) = 1
GMp(0) =  p
electric and magnetic form factors
GEn(0) = 0
GMn(0) =  n
Q2 (GeV/c)2
GEn
r2 rs(r)
r [fm]
GE for the neutron
charge distribution: +ρ core, -ρ fringe, charge radius
April 29, 2005
PV in Electron Scattering at JLab P. A. Souder

5. Strangeness in Nucleons
The charge density of the neutron depends on the radius.
Does the strangeness density of the nucleon
also depend on the radius??
Various theoretical approaches:
Quark models
Dispersion Relations
Lattice Gauge theory
Skyrme models
Chiral Solitons
Data: HAPPEX I;
Effects are surprisingly
small. Due to
cancellations?
April 29, 2005
PV in Electron Scattering at JLab P. A. Souder

6. PV in Electron Scattering at JLab P. A. Souder
The Strangeness Densities can be Measured by Elastic Electroweak Scattering
Measurements must access 0.1 < Q2 < 1
forward and backward angles, three targets
Sensitivity: GEn(Q2=0.2) ~ 0.05,  ~ -0.6
MIT-Bates: SAMPLE
Mainz (Germany): A4
Jefferson Lab: HAPPEX, G0
April 29, 2005
PV in Electron Scattering at JLab P. A. Souder

7. Example at JLab: HAPPEX Experiment
: Q2=0.5 GeV2, 1H
: Q2=0.1 GeV2, 1H, 4He
The HAPPEX Collaboration
California State University, Los Angeles -
Syracuse University -
DSM/DAPNIA/SPhN CEA Saclay -
Thomas Jefferson National Accelerator Facility-
INFN, Rome - INFN, Bari -
Massachusetts Institute of Technology -
Harvard University – Temple University –
Smith College - University of Virginia -
University of Massachusetts –
College of William and Mary
April 29, 2005
PV in Electron Scattering at JLab P. A. Souder

8. New 1H and 4He Data at Q2~0.1 (GeV/c)2
A(Gs=0) = ppm  0.11 ppm
APV = -1.140.24(stat)0.06(stat)ppm
A(Gs=0) =  0.08 ppm
APV = 6.720.84(stat)0.21(syst) ppm
April 29, 2005
PV in Electron Scattering at JLab P. A. Souder

9. Summary of Published 1H and 4He Results
GsE =  0.041(stat)  0.010(syst)  0.004(FF)
GsE GsM =  0.026(stat)  0.007(syst)  0.011(FF)
April 29, 2005
PV in Electron Scattering at JLab P. A. Souder

10. PV in Electron Scattering at JLab P. A. Souder
Add New HAPPEX Results
Dc2 = 1
95% c.l.
Optimistic predictions: GEs~0.07, GMs~0.7
April 29, 2005
PV in Electron Scattering at JLab P. A. Souder

11. World Data vs Q2: Past, Present, and Future
Severe limit on strangeness
If GEs~Q2ρsGEp/4M2
GEs+xGMs
GMs
GEs
Separate form
factors
April 29, 2005
PV in Electron Scattering at JLab P. A. Souder

12. Parity Violating Electron DISZ* * X N
fi(x) are quark distribution functions
For an isoscalar target like 2H, structure functions largely cancel in the ratio:
Provided Q2 >> 1 GeV2 and W2 >> 4 GeV2 and x ~
Must measure APV to fractional accuracy better than 1%
11 GeV at high luminosity makes very high precision feasible
JLab is uniquely capable of providing beam of extraordinary stability
Systematic control of normalization errors being developed at 6 GeV
April 29, 2005
PV in Electron Scattering at JLab P. A. Souder

13. PV in Electron Scattering at JLab P. A. Souder
2H Experiment at 11 GeV
E’: 5.0 GeV ± 10%
lab = 12.5o
Ibeam = 90 µA
60 cm LD2 target
Use both HMS and SHMS to increase solid angle
~2 MHz DIS rate, π/e ~ 2-3
APV = 217 ppm
1000 hours
(APV)=0.65 ppm
(2C2u-C2d)=±0.0086±0.0080
PDG (2004): ± 0.24
Theory:
xBj ~ 0.235, Q2 ~ 2.6 GeV2, W2 ~ 9.5 GeV2
April 29, 2005
PV in Electron Scattering at JLab P. A. Souder

14. PV in Electron Scattering at JLab P. A. Souder
Physics Implications
(2C2u-C2d)=0.012
(sin2W)=0.0009
Examples:
1 TeV extra gauge bosons (model dependent)
TeV scale leptoquarks with specific chiral couplings
Unique, unmatched constraints on axial-vector quark couplings:
Complementary to LHC direct searches
April 29, 2005
PV in Electron Scattering at JLab P. A. Souder

15. PV DIS and Nucleon Structure
Analysis assumed control of QCD uncertainties
Higher twist effects
Charge Symmetry Violation (CSV)
d/u at high x
NuTeV provides perspective
Result is 3 from theory prediction
Generated a lively theoretical debate
Raised very interesting nucleon structure issues: cannot be addressed by NuTeV
JLab at 11 GeV offers new opportunities
PV DIS can address issues directly
Luminosity and kinematic coverage
Outstanding opportunities for new discoveries
Provide confidence in electroweak measurement
April 29, 2005
PV in Electron Scattering at JLab P. A. Souder

16. PV in Electron Scattering at JLab P. A. Souder
Search for CSV in PV DIS
For APV in electron-2H DIS:
u-d mass difference
electromagnetic effects
Direct observation of parton-level CSV would be very exciting!
Important implications for high energy collider pdfs
Could explain significant portion of the NuTeV anomaly
Sensitivity will be further enhanced if u+d falls off more rapidly than u-d as x  1
measure or constrain higher twist effects at x ~
precision measurement of APV at x ~ 0.7 to search for CSV
Strategy:
April 29, 2005
PV in Electron Scattering at JLab P. A. Souder

17. PV in Electron Scattering at JLab P. A. Souder
Higher Twist Effects
Key: APV is known,
so no extrapolations
are necessary 
APV sensitive to diquarks: ratio of weak to electromagnetic charge depends on amount of coherence
If Spin 0 diquarks dominate, likely only 1/Q4 effects
On the other hand, higher twist effects may cancel, so APV may have little dependence on Q2.
April 29, 2005
PV in Electron Scattering at JLab P. A. Souder

18. PV in Electron Scattering at JLab P. A. Souder
APV in DIS on 1H
+ small corrections
Allows d/u measurement on a single proton!
Vector quark current! (electron is axial-vector)
Determine that higher twist is under control
Determine standard model agreement at low x
Obtain high precision at high x
April 29, 2005
PV in Electron Scattering at JLab P. A. Souder

19. Deuteron analysis has nuclear
d/u at High x
Deuteron analysis has nuclear
corrections
APV for the
proton has no such
corrections
The challenge is to get statistical and systematic errors ~ 2%
April 29, 2005
PV in Electron Scattering at JLab P. A. Souder

20. Summary of PV DIS Program
Hydrogen and Deuterium targets
Better than 2% errors
It is unlikely that any effects are larger than 10%
x-range
W2 well over 4 GeV2
Q2 range a factor of 2 for each x point
(Except x~0.7)
Moderate running times
With HMS/SHMS: search for TeV physics
With larger solid angle apparatus: higher twist, CSV, d/u…
April 29, 2005
PV in Electron Scattering at JLab P. A. Souder

21. Large Acceptance: Concept
CW 90 µA at 11 GeV
40-60 cm liquid H2 and D2 targets
Luminosity > 1038/cm2/s
JLab Upgrade
Need high rates at high x
For the first time: sufficient rates to make precision PV DIS measurements
solid angle > 200 msr
Count at 100 kHz
online pion rejection of 102 to 103
April 29, 2005
PV in Electron Scattering at JLab P. A. Souder

22. PV in Electron Scattering at JLab P. A. Souder
Summary
Strange Quarks and Elastic Scattering
Hint of positive effect
More data soon (G0, HAPPEX II)
Parity Violation in DIS (JLab at 11 GeV)
Electroweak test
Hadron structure
d/u at large x
δu-δd (Charge symmetry violation)
Clean higher twist study
April 29, 2005
PV in Electron Scattering at JLab P. A. Souder