Transcript Strangeness in the Nucleon Newest Results from HAPPEx and G0

Strangeness in the Nucleon
Newest Results
from HAPPEx and G0
• Physics case
• Electroweak Standard Model
• Experimental Aspects
• Results and Perspectives
Erice, Sept. 2007
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Physics Case
•Nucleon Structure:
Valence quarks dressed by gluon
exchange and qq fluctuations.
Quark sea, key component on the
nucleon.
•Strangeness in the nucleon:
s quark flavor decouples from valence
quarks but may still be light enough
to contribute.
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“Low Q” physics
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Strange Quarks in the Nucleon
Strange sea measured in N scattering
Strange sea is well-known, but
contributions to nucleon matrix
elements are somewhat unsettled:
•Spin
polarized DIS
Inclusive: Ds = -0.08 ± 0.05
Semi-inclusive: Ds = 0.03 ± 0.03
•Strange mass
pN scattering: 0-30%
N ss N
•Strange vector Form Factor
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N s   5 s N
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
N s s N
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Form Factors
Elastic scattering off a static potential (no spin):
d d
2

 F(q)
d d pt
(q)
Z(r)ddr
F(q) 
iq.r
3
e

(r)d
r


 Direct image of the charge distribution inside
limit of no recoil (Q2<M2).
the target, in the
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Electromagnetic Form Factors
Nucleon target: 2S+1 form factors
e-
1 2 2
GE (Q )  QN  Q r  (Q4 )
6
GM (Q2 )  N  (Q2 )

(q)
p,n

2
Charge
Magnetization
FT
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
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u-d Flavour Separation
 ,,pp 22 u,u p 11 dd, p

GEE,M
 G
GE,M
 G
GEE,M
,M 
E,M 
,M
G

3
3
3
3


22 u,n
11 du,n
,n
d
G

GEE,n,M

G

GEE,M
GE,M
G
,M 
E,M 
,M


33
33
e-
(q)
Charge
symmetry


QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
s quarks distributions? GEs(0) = 0, no other symmetry constraints…
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
Weak Form Factors
Z ,p
GE,M
(Q2 )
e-
Vector
Z0 (q)

 GAe (Q2 ),GP (Q2 )
Axial
3 flavors separation:

  , p 2 u
1 d
1 s
G

G

G

GE,M
 E,M
E,M
E ,M
3
3
3

s
2
p
n
Z

(1
4
sin

)G

G

G
 G
2 d
1 u
1 Ws
E,M
E,M
E,M
,n E,M
G

G

G

G
 E,M
E,M
E ,M
E,M
3
3
3

0 new probe of the nucleon, only assumes charge sym.
 8 2  u
 4 2  d
 4 2  s
 •Z Z
,p
 1 sin
W-G
Sensitive
to (s
s E,M
).  1 sin W GE,M  1 sin W GE,M
G•E,M
 3

 3

 3


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Parity Symmetry
•Electromagnetism
•Gravitation
•Strong interaction
O
•Weak interaction
Sym. miroir
ggg
r,p,E
g g g
-r,-p,-E
Pseudo-vector:
g g gg
=rLp,B
g g
+,+B
Scalar
m
+m
g g
h=.p
-h
Vector
:
:
Pseudo-scalar :
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1957 !
T.D.Lee/C.N.Yang
Propose to test PV
in weak interactions
Measure a
Pseudoscalar…
C.S. Wu
 decay of
polarized 60Co
JP

M. Gell-Mann/R. Feynman e
Lee & Yang
(V-A) theory
M. Goldhaber
Left handed neutrino
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
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Electroweak Standard Model
f
Z0
(CERN, 1973)
f
Partial P in neutral weak current
 electroweak unification.
•Weak isospin group SU(2)L:
e  u
   
 L d L
JZ0 = J3 – sin2W Jem
e±
J+, J-, …. J3
SU(2)LxU(1)Y
W+, W-, …. Z0
W±


(V-A)
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GF
g2
g  e,

2 8MW2
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cfV = T3 – 2sin2WQf
cfA = T3
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-Z0 Interference
2
e-
e-
 = |MMZ
|2
(Q)
=
Z0 (Q)
+
Scale  ~ 1 fm
Q2
<<
GF
MZ ~
2
MZ2
<< M ~
4 p
Q2
Z0 contribution in the cross section is negligible…

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
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Parity Violating Asymmetry
Lee & Yang: measure a pseudoscalar quantity
APV, generated by helivcity flip of the e- beam
NL
NR
APV
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M M Z*
NR  NL
GF Q2
6




10
!
2
NR  NL
M
4p 2
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E122@SLAC
b
ee-
PVDIS
2H
APV 
X
a
2
GF Q
a(x)  f (y)b(x)
2p
x  x Bjorken y  1 E / E
Isoscalar target: a and b ~ cst (@ large x)


a(x) 
C.Y. Prescott et al., 1978
3 
(2C1u  C1d )
10
3 
uv (x)  dv (x)
b(x)  (2C2u  C2d )

10 
u(x)  d(x) 
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APV~10-4 ± 10-5
sin2W = 0.224 ± 0.020
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Weak Form Factors
Proton target:
1
APVH
AE   GEpGEZ ,
GF Q2 AE  AM  AA
~ few parts per million
 

p
4p 2 
AM   GMp GMZ ,


AA   1  4 sin 2 W  'GMp GAe

Forward angle
4He
4
APVHe
target: GEs alone
Backward angle
2H

GF Q  2
GEs

sin W 
p
n 
2(G

G
p 2 
E
E ) 
2
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target:
enhanced GAe sensitivity
2
H
PV
A
 p Ap   n An

 p  n
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Experimental Strategies
SAMPLE
(MIT-Bates)
1998-02
HAPPEX
(JLab)
1998-99
HAPPEX II
(JLab)
2004-05
PVA4
(MAMI)
2002-08
G0
(JLab)
2003-06
Q2(GeV/c2)
0.04, 0.1
0.48
0.1
0.1, 0.23
0.12 - 1.0
Angle
B
F
F
F/B
F/B
Target
H, D
H
H, 4He
H,D
H, D
Separation
GMs,GA
Ges+0.4GMs
Ges, GMs
Ges, GMs
Ges, GMs,GA
G0 : Large , Particle id, large Q2 range
HAPPEx : small , integrating, single accurate Q2
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Experimental Challenges
APV
1
1 Araw  Abeam  Pe Abkg f bkg
  Aexp  
Pe
Pe
1 f bkg
Aexp
Aexp


stat
1
Pe  APV  N
Goal: down to ~50 ppb absolute error and 2% relative

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• High rate
• High beam polarization
• Control of beam asymmetries
• Background rejection
• Normalization
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« Table Top » Experiments
DAQ
No “external” instrumentation:
•Control of the polarized source
•Redundant beam monitoring
from injector to experimental
hall
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The Polarized e- Source
•Optical pumping of strained GaAs
cathode produces highly-polarized
e- beam.
•“Strain” boosts polarization but
introduces anisotropy in response.
•Rapide and pseudorandom helicity flip.
•Pair asymmetry measured several
million times to reach stat. error.
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Beam Asymmetries
Beam Axis
N R,L  dR,L
Intensity:
APV
N  I   N  I
  
A exp AI


N I N I
Position:

Typical sensitivity: 10ppm/m
• Azimuthally symmetric detector
DX=XR-XL
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• Most h.c. beam asymmetries
trace back to differences in
preparation of circularly polarized
laser light at the source.
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PITA Effet
Polarization Induced Transport Asymmetry
Perfect ±/4 retardation
leads to perfect D.o.C.P.
•Now L/R states have opposite
sign linear components.
A common retardation offset
over-rotates one state,
under-rotates the other
Right helicity
Left helicity
•This couples to “asymmetric
transport” in the optics
system to produce an
intensity asymmetry.
This is the D phase
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Intensity Asymmetry using RHWP
maximum
analyzing
power
Electron beam intensity
asymmetry (ppm)
minimum
analyzing
power
A rotatable /2 plate
downstream of the
P.C. allows arbitrary
orientation of DoLP
Rotating waveplate angle
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4 term measures
Ana Power*DoLP
(from Pockels cell)
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Optics
Table
High Pe
High Q.E.
Low Apower
Strategy
• Rapid, pseudorandom helicity flip.
controls
effective
analyzing
power
Intensity
Attenuator
Slow helicity
reversal
Tune
residual
linear pol.
(charge
Feedback)
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•Careful config. to
reduce beam asym.
•Feedback systems
to zero residual
asym. measured in
exp. hall.
•Further cancellation
by slow helicity
reversals.
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Feedback
Reduce remaining effects
Position (G0)
charge
Performances:
AI < 1 ppm
Dx ~ 1 nm
10 ppb final correction
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Figures from K.Nakahara
Cates et al., NIM A vol. 278, p. 293 (1989)
T.B. Humensky et. al., NIM A 521, 261 (2004)
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Slow Reversals
Asymmetry (ppm)
Pure statistical distribution of
the pair asymmetries
Helicity Window Pair Asymmetry
Slug
Sign flip of APV under insertion /
removal of the half-wave plate at
the source
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E~3GeV,
=6° Q2~0.1
GeV/c2
JLab Hall A
Polarimeters
Compton
1% syst
Continuous
Target
Møller
2% syst
400 W transverse flow
20 cm, LH2
20 cm, 200 psi 4He
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High Resolution Spectrometer
S+QQDQ
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5 mstr over 4o-8o
25
Happex Detectors
Overlap the elastic line above the
Very clean separation of
elastic events by HRS optics  focal plane and integrate the flux
Elastic Rate:
1H:
PMT
100 x 600 mm
120 MHz
4He:
Cherenkov
cones
12 m dispersion
sweeps away
inelastic events
PMT
12 MHz
A
D
C

Large dispersion and heavy
shielding reduce backgrounds at

the focal plane
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JLab Hall C
Detector
wheel
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
G0 beam
monitoring
girder
Superconducting
magnet
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G0 Detectors
Forward angle configuration
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
protons
 GEs  GMs
Magnet
Q2=0.1-1.0 GeV/c2
Detectors

Inelastic
protons
Beam
elastic
protons
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
p+
Target
Erice, Sept. 2007
ToF histogram
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G0 Detectors
Backward angle configuration
 GMs ,GAe
CED + Cherenkov
FPD
electrons
e- beam
target
e~110°
Magnet

Beam
362
Q2
(GeV2)
0.23
686
0.62
Ee (MeV)
Target
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Polarimetry
Main normalization error, Aexp = Pe.APV
- Moller polarimetry in hall C:
solid target saturated in high B field
1.3% relative accuracy
Interleaved runs at low current
- Compton polarimetry in hall A:
continuous monitoring
FOM strongly depends on Ebeam
1.0% relative accuracy @ 3GeV
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Results @ Q2=0.1 GeV/c2
HAPPEX only :
APVh=-1.58± 0.12 ± 0.04 ppm
APVHe=6.40 ± 0.23 ± 0.12 ppm
GMs = 0.18 ± 0.27
GEs = -0.005 ± 0.019
Global fit:
GMs = 0.22 ± 0.20
GEs = -0.011 ±
0.016
<6% de p, <5% rs
(95% CL)
R.D.Young, et al, hep-ph/0704.2618
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Results @ Q2=0.1 GeV/c2
16. Skyrme Model - N.W. Park and H.
Weigel, Nucl. Phys. A 451, 453
(1992).
17. Dispersion Relation - H.W. Hammer,
U.G. Meissner, D. Drechsel, Phys.
Lett. B 367, 323 (1996).
18. Dispersion Relation - H.-W. Hammer
and Ramsey-Musolf, Phys. Rev. C 60,
045204 (1999).
19. Chiral Quark Soliton Model - A.
Sliva et al., Phys. Rev. D 65, 014015
(2001).
20. Perturbative Chiral Quark Model V. Lyubovitskij et al., Phys. Rev. C 66,
055204 (2002).
21. Lattice - R. Lewis et al., Phys. Rev. D
67, 013003 (2003).
22. Lattice + charge symmetry Leinweber et al, Phys. Rev. Lett. 94,
212001 (2005) & hep-lat/0601025
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Q2 Dependence
Proton
Data
• Small strange quarks contribution at low Q2
• G0 and PVA4 backward results to be released soon
• Happex-III likely to run in 2009
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Projected G0 Results
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Perspectives
PRex: APV in elastic e--208Pb scattering
(JLab Hall A)
Goal: Rn/Rn~1%
•Z0 couples mainly to neutrons:
--> new accurate measurement independent
of nuclear models, pins down sym. energy
--> Constraint on neutron stars structure
Lead
APV
 50015ppb
C.J. Horowitz, Phys. Rev. C 64, 062802 (2001)

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
Perspectives
Test of the Standard Model at Low Energy
Combining global fit and extrapolation to
Q2=0 sets new limits on C1q and
constrains new physics at the TeV scale:
p
ApPV  A0 Qweak
Q2  BQ4 
Qweak @ JLab
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
ApPV (Q2  0.03GeV /c 2 )  230 5(stat ) ppb
--> Further improvement by a factor 5
PV-DIS @ JLab
•Constraint the C2q axial couplings
using isoscalar target
•New generation E122 exp. @ JLab
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R.D.Young, et al,
hep-ph/0704.2618
36
Running of sin2w
sin  (Q) 
2
eff
W
 (0) sin 2 W (mZ ) MS
MollerJlab
Qweak
E158
LEP-SLC
(0)=1.03
sin2eff (E158) =
0.2397 ± 0.0013
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Summary
•Tremendous progress in experimental techniques over
last 10 years
• Study of the strange nucleon form factors almost
completed. Stringent upper limits already set at low Q2.
•Weak neutral current at low energy established as a
new probe of the nucleon … and the weak interaction
itself.
•Perspectives at the crossing of nuclear, particle and
astro physics with PRex and test of SM at low energy.
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