1. Nucleon Strangeness: What we know and what we are still missing
Jacques Arvieux
IPN-Orsay
Hadron Structure at J-PARC, Tsukuba, 1 December 2005

2. DIFFERENT TYPES OF POSSIBLE STRANGE CONTRIBUTIONS
SCALAR
and magnetic moment
AXIAL
VECTOR
(current and magnetization)

3. WHAT ROLE DO STRANGE QUARKS PLAY?
proton u u
valence quarks d u
gluon
“non-strange” sea (u, u ,d, d ) u s
“strange” sea (s, s) quarks s
Mass:
(scalar)
Momentum:
Spin:
(axial)
Charge and current:
(vector)

4. NUCLEON FORM-FACTORS IN ELASTIC SCATTERING (vector term)
well defined experimental observables
provide an important benchmark for testing non-perturbative QCD structure of the nucleon
electromagnetic form factors
Precision of EM form factors in GeV2 Q2 range ~ 2 - 4%
neutral weak form factors
Weak amplitude = 10-5 x Electromagnetic Amplitude

5. PARITY VIOLATING ELECTRON SCATTERING
polarized electrons, unpolarized target
At tree level:
Strange electric and magnetic form factors
+ axial form factor
At a given Q2 decomposition of GsE, GsM, GeA
Requires 3 measurements:
Forward angle e + p (elastic)
Backward angle e + p (elastic)
Backward angle e + d (quasi-elastic)
e+ He4 elastic scattering (only GsE)

6. PARITY VIOLATING ASYMMETRY
forward angles
HAPPEX, Mainz, G0: sensitive to
backward angles
SAMPLE, G0: sensitive to
and
and
Overall goal of parity-violating electron scattering programs:
axial
form factor!
Determine and separately over a wide range
(0.1 – 1.0) (GeV/c)2 of Q2

7. ELECTROWEAK CORRECTIONS
ASYMMETRY INCLUDING
ELECTROWEAK CORRECTIONS
with
and

8. CORRECTIONS TO TREE LEVEL
CALCULATIONS
To determine the strange form factors we must measure the PV
asymmetry and compare it to the non-strange asymmetry A0 where
strange form factors GES and GMS are set to zero.
BUT WHAT IS REALLY A0?
To the tree level calculations one should apply the following
corrections:
1) One-quark electroweak corrections (Standard Model)
2) Multiquark radiative corrections (Anapole Moment)
and make the best choice for the following parameters:
3) Choice of electromagnetic form-factors
5) Axial form-factor, including Ds (next talk)

9. ELECTROWEAK RADIATIVE CORRECTIONS.
1) One quark corrections:
electroweak radiative
corrections to e-N scattering . . .
2) Multi-quark corrections:
nucleon anapole moment
(parity-violating coupling between quarks) . . . .
Z,W
Anapole moment

10. PROTON FORM-FACTORS Rosenbluth separation Recoil polarization
Comparison of Friedrich-
Walcher (blue) and Kelly
(green) fits for GEp and GMp
Rosenbluth separation
Recoil polarization

11. NEUTRON FORM FACTORS
The uncertainties are much larger than for protons and GEn data do not extend to high Q2 data so that this effect is not visible:
GEn
GMn

12. REVIEW OF EXISTING EXPERIMENTAL RESULTS
1) SAMPLE (MIT-Bates): 3 experiments
1 exp on hydrogen in 1998 at Q2 = 0.1 (GeV/c)2
1 exp on deuterium in 1999 at Q2 = 0.1 (GeV/c)2
1 exp in 2001 at Q2 = 0.03 (GeV/c)
2) HAPPEX (Jefferson-Lab): 4experiments
1 exp in 1998 at Q2 = 0.45 (GeV/c)2
2 experiments on He and H at Q2 = 0.1 (GeV/c)2
3) PV-A4 (MAMI-Mainz): 2 experiments
1 exp at on H Q2 = 0.23 (GeV/c)2 published in Jan 2004
1 exp on H at Q2 = 0.1 (GeV/c)2 published in Dec 2004
G0 (Jefferson Lab): Q2 = (GeV/c)2
forward angles on H target in 2004
backward angles on H and D target in 2006

13. GENERAL EXPERIMENTAL REQUIREMENTS
Want to measure APV ~ -3/-40 ppm with precision dAPV /APV ~ 5%
Statistics (need events):
Reliable high polarization, high current polarized source
High power H/D target
Large acceptance detector
High count rate capability detectors/electronics
Systematics (needed to reduce false asymmetries, accurately measure dilution factors):
Small helicity-correlated beam properties
Capability to isolate elastic scattering from other processes

14. SUMMARY OF SAMPLE 200 MeV DATA
Q2=0.1 (GeV/c)2 D2 H2
Zhu, et al.
Using Zhu et al. for GAe(T=1)
Combined D2/H2 at 200 MeV

15. HAPPEX I RESULTS

16. 2004 HAPPEX-II Results HAPPEX-4He:
Q2 = (GeV/c)2
APV =  0.84 (stat)  0.21 (syst) ppm
A(Gs=0) = ppm  ppm
GsE =  0.041(stat)  0.010(syst)  0.004(FF)
Q2 = (GeV/c)2
APV =  0.24 (stat)  0.06 (syst) ppm
HAPPEX-H:
A(Gs=0) = ppm  ppm
GsE GsM =  0.026(stat)  0.007(syst)  0.011(FF)

17. RESULTS FROM PV-A4 (MAMI-MAINZ)
Note the
Negative sign

18. PRESENT RESULTS BEFORE G0
GES ~ 0
GMS ~ +0.5 mP
GEs + a(Q2) GMs
GMs
GEs
Q2 [GeV2]

19. THE G0 EXPERIMENT AT JLAB
Caltech, Carnegie-Mellon, W&M, Hampton, IPN-Orsay, ISN-Grenoble, Kentucky, La.Tech, NMSU, Jlab, TRIUMF, Uconn, UIUC, UMan, UMd, UMass, UNBC, VPI, Yerevan
Goal: Determine contributions of strange quarks to charge and
magnetization distributions of the nucleon within a few
percent of Gdipole for Q2 = (GeV/c)2
Forward and backward angle parity-violating e-p elastic and e-d quasielastic in Jefferson Lab Hall C
Kinematics
Forward mode: detect recoil protons
Backward mode: detect electrons
Note that G0= (Gu + Gd + Gs) / 3 is the singlet form-factor

20. G0 in Hall C at JLAB superconducting magnet (SMS) cryogenic supply
beam
monitoring
girder
scintillation detectors
cryogenic target ‘service module’
electron beamline

21. Parity Quality Beam
Total of 744 hours (103 Coulombs) of parity quality beam with a 4 cut on parity quality.
Beam Parameter
Achieved
“Specs”
Charge asymmetry
-0.14 ± 0.32
ppm
1 ppm
x position differences
3 ± 4 nm
20 nm
y position differences
4 ± 4 nm
x angle differences
1 ± 1 nrad
2 nrad
y angle differences
1.5 ± 1 nrad
Energy differences
29 ± 4 eV
75 eV
All parity quality specs have been achieved!!

22. G0 DATA: GEs + h GMs
F&W
Arr
HAPPEX
lines show Friedrich & Walcher, Arrington/Kelly form factors (Kelly = 0)
HAPPEX points adjusted to G0 incident energy (DA = 0.03 ppb, 0.13 ppm)
DHB 15 May 05

23. World Data @ Q2 = 0.1 GeV2 GE s GM s = -0.013  0.028 = +0.62  0.31
Contours
1s, 2s
68.3, 95.5% CL
Theories
Leinweber, et al. PRL 94 (05)
Lyubovitskij, et al. PRC 66 (02)
Lewis, et al. PRD 67 (03)
Silva, et al. PRD 65 (01)
Fix figure

24. WORLD DATA: Q2 = 0.23 GeV2 Good agreement between G0 and PV-A4
Need backward angle data for separating GEs and GMs
DHB 15 May 05

25. World data: Q2 = 0.477 GeV2 Good agreement between G0 and HAPPEX
HAPPEX H G0
Good agreement between G0 and HAPPEX
Need backward angle data for separating GES and GMS
DHB 15 May 05

26. CONCLUSIONS
Fist measurement of strange form factors at high momentum transfer by G0
Contribution of strange quarks to nucleon form factors is small but definitely non-zero
Backward angle data from PVA4 and G0 , combined with new forward HAPPEX point will allow a clean GES / GMS separation
Final precision hampered by uncertainties in some parameters:
- neutron electric form factor
- Ds
- Axial form factor (next talk…….)

27. END