1. Deep Inelastic Parity Robert Michaels, JLab Electroweak Physics
Thanks to Paul Souder, Paul Reimer, Peter Bosted, Xiaochao Zheng, Kent Paschke, Krishna Kumar
Robert Michaels, JLab
Electroweak Physics
Hadronic Physics
Possibilities with MAD / HMS / SHMS
New Toroidal Spectrometer
June 20, 2005
DIS Parity at 11 GeV

2. Parity Violating Asymmetry2 +
Applications :
Nucleon Structure (e.g. strangeness)
Nuclear Structure (neutron density)
Standard Model tests ( )
June 20, 2005
DIS Parity at 11 GeV

3. Standard Model Tests Q DIS Moller weak
The standard model of electroweak interaction :
Experimentally very successful
But seems it must break down !!
(issues: many parameters, origin of mass,
unification with gravity, etc)
Frontiers:
1. Higher energy
2. Higher precision  JLab parity p Q
DIS
Moller
weak
(this talk)
June 20, 2005
DIS Parity at 11 GeV

4. 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
June 20, 2005
DIS Parity at 11 GeV

5. Electron-Quark PhenomenologyV V A
C1u and C1d will be determined to high precision by other experiments
C2u and C2d are small and poorly known: can be accessed in PV DIS
New physics such as compositeness, new gauge bosons:
Deviations to C2u and C2d might be fractionally large
Proposed JLab upgrade experiment will improve knowledge of 2C2u-C2d by more than a factor of 20
June 20, 2005
DIS Parity at 11 GeV

6. 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
June 20, 2005
DIS Parity at 11 GeV

7. 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
June 20, 2005
DIS Parity at 11 GeV

8. 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
June 20, 2005
DIS Parity at 11 GeV

9. Search for CSV in PV DIS For APV in electron-2H DIS: Strategy:
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:
June 20, 2005
DIS Parity at 11 GeV

10. Higher Twist Effects 
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.
Novel interference terms might contribute
On the other hand, higher twist effects may cancel, so APV may have little dependence on Q2.
June 20, 2005
DIS Parity at 11 GeV

11. 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
xBj ~ 0.235, Q2 ~ 2.6 GeV2, W2 ~ 9.5 GeV2
1000 hours
(APV)=0.65 ppm
(2C2u-C2d)=±0.0086±0.0080
PDG (2004): ± 0.24
Theory:
Advantages over 6 GeV:
Higher Q2, W2, f(y)
Lower rate, better π/e
Better systematics: 0.7%
June 20, 2005
DIS Parity at 11 GeV

12. 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
June 20, 2005
DIS Parity at 11 GeV

13. 50% azimuthal coverage assumed
6 GeV
50% azimuthal coverage assumed
June 20, 2005
DIS Parity at 11 GeV

14. 2 to 3.5 GeV scattered electrons 20 to 40 degrees
Factor of 2 in Q2 range at moderate x
High statistics at x=0.7, with W>2
June 20, 2005
DIS Parity at 11 GeV

15. Large range in Q2 for HT study
Cut on 0.6<y<0.8
Large range in Q2 for HT study
High x (>0.7) accessible with W2>4
Large acceptance allows feasible runtime requests
p/e ratio is not extreme
June 20, 2005
DIS Parity at 11 GeV

16. Deuteron analysis has nuclear
d/u at High x
Deuteron analysis has nuclear
corrections
APV for the
proton has no such
corrections
Must simultaneously constrain higher twist effects
The challenge is to get statistical and systematic errors ~ 2%
June 20, 2005
DIS Parity at 11 GeV

17. d/u Measurements for Proton
(Kent Paschke simulation)
A couple weeks of beam time with toroid spectrometer
June 20, 2005
DIS Parity at 11 GeV

18. d/u of Proton Compare MAD Spectr. to Toroid Spectr. d/u June 20, 2005
DIS Parity at 11 GeV

19. EMC effect in Parity Violation ?
50 days each plot.
Solid targets are 1% radiation length.
Cross section data from J. Gomez et.al. PRD 49 (1994) 4348
June 20, 2005
DIS Parity at 11 GeV

20. PV DIS Program Hydrogen and Deuterium targets
Perhaps heavier nuclei (EMC effect)
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…
June 20, 2005
DIS Parity at 11 GeV