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provide an important benchmark for testing non-perturbative QCD ... 1 exp on deuterium in 1999 at Q2 = 0.1 (GeV/c)2. 1 exp in 2001 at Q2 = 0.03 (GeV/c) ... – PowerPoint PPT presentation

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Title: Pr


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 (scalar) Spin (axial) Ch
arge and current (vector)
4
NUCLEON FORM-FACTORS IN ELASTIC SCATTERING
(vector term)
  • Nucleon form factors
  • 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 0.1 - 1 GeV2 Q2
range 2 - 4

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)

4. 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
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
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 0.1-1 (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 1013 - 1014 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
Q20.1 (GeV/c)2
Using Zhu et al. for GAe(T1)
Combined D2/H2 at 200 MeV
15
HAPPEX I RESULTS
16
2004 HAPPEX-II Results
HAPPEX-4He
Q2 0.091 (GeV/c)2 APV 6.72 ? 0.84 (stat) ?
0.21 (syst) ppm
A(Gs0) 7.507 ppm ? 0.075 ppm GsE -0.039
? 0.041(stat) ? 0.010(syst) ? 0.004(FF)
Q2 0.099 (GeV/c)2 APV -1.14 ? 0.24 (stat) ?
0.06 (syst) ppm
HAPPEX-H
A(Gs0) -1.440 ppm ? 0.105 ppm GsE 0.08
GsM 0.032 ? 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, WM, 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
0.12-1.0 (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 20 nm
x angle differences 1 1 nrad 2 nrad
y angle differences 1.5 1 nrad 2 nrad
Energy differences 29 4 eV 75 eV
All parity quality specs have been achieved!!
22
G0 DATA GEs h GMs
  • 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 _at_ Q2 0.1 GeV2
-0.013 ? 0.028
0.62 ? 0.31
? 0.62 2s
  • Contours
  • 1s, 2s
  • 68.3, 95.5 CL
  • Theories
  • Leinweber, et al. PRL 94 (05) 212001
  • Lyubovitskij, et al.PRC 66 (02) 055204
  • Lewis, et al.PRD 67 (03) 013003
  • Silva, et al.PRD 65 (01) 014016

http//www.npl.uiuc.edu/exp/G0/Forward
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 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
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