Transcript PVES Strange Quark Contribution to the Charge and Magnetization of the Nucleon What can we measure? • • • • Nucleon structure Nuclear structure Electron weak charge Proton weak charge – Weak.

PVES
Strange Quark Contribution to the
Charge and Magnetization of the
Nucleon
What can we measure?
•
•
•
•
Nucleon structure
Nuclear structure
Electron weak charge
Proton weak charge
– Weak coupling constants
• SM Tests
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June 1-19, 2015
2
Program
Expt/Lab
Target/
Angle
Q2
(GeV2)
Aphys
(ppm)
Sensitivity
Status
LH2/145
LD2/145
LD2/145
0.1
0.1
0.04
-6
-8
-4
ms + 0.4GA
ms + 2GA
ms + 3GA
2000
2004
2004
LH2/12.5
LH2/6
4He/6
LH2/14
0.47
0.11
0.11
0.63
-15
-1.6
+6
-24
GE + 0.39GM
GE + 0.1GM
GE
GE + 0.5GM
2001
2006, 2007
2006, 2007
2009
LH2/35
0.23
-5
GE + 0.2GM
2004
LH2/35
0.11
-1.4
GE + 0.1GM
2005
LH2/145
0.23
-17
GE + ηGM + η’GA
2009
LH2/35
0.63
-28
GE + 0.64GM
2009
LH2/35
LH2/LD2/110
0.1 to 1
0.23, 0.63
-1 to -40
-12 to -45
GE + ηGM
GE + ηGM + η’GA
2005
2009
SAMPLE/Bates
SAMPLE I
SAMPLE II
SAMPLE III
HAPPEx/JLab
HAPPEx
HAPPEx II
HAPPEx He
HAPPEx
A4/Mainz
G0/JLab
Forward
Backward
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Nucleon Structure
• Proton is both ordinary and extraordinary object
•
•
50% of mass of visible universe
masses of constituents ~ 1% of its total mass
• What is it made of?
q
q
– valence quarks carry
baryon number
– sea of gluons
– and associated quarkantiquark pairs
• analog of Lamb shift
– very complicated because
• strong coupling ●
• gluons interact with each
other
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→ many-body physics with
virtual particles
4
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Structure Functions
Deep Inelastic Scattering
x - fraction of momentum carried
by the struck quark
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EM Structure of the Nucleon
Elastic Scattering
Electric and magnetic form factors
J EM ,e
EM , N
GE  F1  F2
N
GM  F1  F2
J
Way of parameterizing this blob
J EM ,e  eie  e
N J EM,N N  N [] N
[



i

q

2
2
]   F1 ( q )  
F2 ( q )
2M N 
 

Dirac
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June 1-19, 2015
Pauli
7
EM Structure of the Nucleon
Related to the charge and
magnetization distributions
within the nucleon
GE  F1  F2
GM  F1  F2
GMp (0)   p
G ((0)
0) 
 qq
G

ee

pp
E
E
 2.79  N
GEn (0)  q
0
GMn (0)  n
 1.91 N
__
Neutron Electric
Charge Distribution
 (u d)
p (u u d)
“pion cloud”
n (u d d)
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EM Structure of the Nucleon
G (0)  q
p
E
J EM ,e
 e
J
GEn (0)  q

GE  F1FF
22


GM  F1  F22
0
GMn (0)  n
 1.91 N
(Electric and magnetic
form factors)
J EM ,e  eie  e
N J EM,N N  N [] N
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 2.79  N
EM , N
N
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GMp (0)   p
[
iiqq   2 2 
  22
]   F11 ((qq ))
FF2 2( q( q))
22MMNN 
 

Dirac
Dirac
Pauli
Pauli
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Weak Structure of the Nucleon
Z
NC ,e
J
NC , N
J
N
GEZ  F1Z  F2Z
GMZ  F1Z  F2Z
NC ,e
J
 ei[ g   g   ] e
NC, N
N J
[
 Z 2

i  q Z 2
]   F1 ( q )  
F2 ( q )  
2M N




e
V 
e
A 5 
Dirac
Pauli
    5GAZ ,N
N   N [] N
parity violation b/c of this
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Strangeness in the Nucleon
Nucleon in QCD
How much do virtual ss¯ pairs
contribute to the structure of
the nucleon?
1
Momentum:
 x(s  s)dx
~ 4% (DIS)
0
Spin:
Mass:
Charge and current:
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 N | s    s | N  ~ 0 to10% (polarizedDIS)
 N | ss | N  ~ 0 to30% (N - term)
 N | s  s | N   ??  GEs GMs
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Quarks in the Nucleon
T henucleon wavefunction is :
|N  
| uud   | uudg   | uudss   | uuduu  ...
q
q
J EM ,N  Qi qi  qi
i
J NC ,N  QiZ qi  qi
i
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StRanGe quark contribution
Define thenucleonformfactorsassociatedwith a given quark current
q as :
 q
i  q 
q
 N
N | q   q | N   N  F1    F2
2M N  and we have
Assume
isospin symmetry

G  F FF
q
E
q
1
q
222
q
q
q
G

F

F
1 M 1 F11  2F2

  u

3
3   GE , M 
 GE , M   3
  ,n 
 d 
and this
1
2
1
   GE , M 
 GE , M    
3  s 
are well known
 G Z , p   Z3 3Z
Z
 E ,M   Qu Qd Qs  GE ,M 




what about this?
Q
this
 ,p
(Assume neutral weak charges are known)
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QZ
1  8/3 sin2W
u
+2/3
d
s
1/3 1 + 4/3 sin2W
1/3 1 + 4/3 sin2W
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Isolating form factors
For a proton:
  GF Q 2  AE  AM  AA
A

p
 4 2 
AE   GE , p GEZ , p ,

AM   GM , p GMZ , p ,
Forward angle
~ few parts per million

AA   1  4 sin 2 W  'GM , p G Ae
Backward angle
Q2

4M p
 

  1  2(1   ) tan2 e 
2

For
4He: G s
E
APV
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    (1   )(1   2 )
alone
GF Q 2

 2
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 2

GEs
sin W 
p
n 
2
(
G

G
E
E )

For deuteron:
enhanced GAe sensitivity
Ad 
 p Ap  n An
d
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1
The Axial Current Contribution
AE   GE , p GEZ , p ,


AM   GM , pGMZ , p ,
Z
AA   1  4 sin 2 W  'GM , pGAe

e
– “unknown form factor” GeA (Q2)
– related to form factor measured in neutrino
scattering
– also contains “anapole” form factor
– determine isovector (T=1) piece by combining
proton and neutron (deuteron) measurements

a
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Classical analog: torque on a toroidal
magnetic field in an external current
field
June 1-19, 2015
p
“box”

Z
e
p
“mixing”
e

p
“quark pair”
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•
What is the Anapole Moment?
As first noted by Zel’dovich (Sov. Phys. JETP 6 (58) 1184), a parity-violating
coupling of the photon can occur
p'
J  (Q 2 )

F2 (Q 2 )
2

p  u ( p' ) F1 (Q )   i

q 


2M

FA (Q 2 )
M
2


FE (Q 2 )
 
q    q q  5  i
  q  5 u ( p)
2M

2
where FA and FE are the anapole (parity-violating, time-reversal conserving) and
electric dipole (parity- and time-reversal- violating) moments, respectively
• At low Q2 the corresponding interaction energy is
(Musolf and Holstein,
Phys. Rev. D 43 (91) 2956)

FA
2 FA 



j
~

e


j
 5

2
2
M
M
The classical analog of the anapole moment is that property of a
toroidal magnetic field that leads to a torque in an external current
field
Lanapole  e 2
•
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
a

j
 
U   a  j
  
 a x j
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G0 Experiment
Super-conducting
magnet (SMS)
Target service
module
G0 Beam
monitors
LUMIs
Ferris wheel
FPD
Mini-ferris wheel
CED+ Cerenkov
View from downstream
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View from ~upstream
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Turn-around of G0 Detector – Aug. 11, 2005
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Turn-around of G0 Magnet – Aug. 23, 2005
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G0 Experiment
CED + Cerenkov
FPD
e- beam
target
LUMIs
(not shown)
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Rate Corrections
•
Correct the yields for random coincidences
and electronic deadtime prior to asymmetry
calculation
randoms small except for D-687 (due to
higher pion rate)
Direct (out-of-time) randoms measured
- Validated with simulation of the
complete electronics chain
•
•
Data
set
Correction
to Yield (%)
Asymmetry
Correction
(ppm)
systematic
error (ppm)
H 362
6
0.3
0.06
H 687
7
1.4
0.17
D 362
13
0.7
0.2
D 687
9
6
1.8
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Deadtimes (%)
H 687 MeV
H 362 MeV
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Background Corrections
A
Ameas  f bkgd Abkgd
1  f bkgd
Data set
ΔA
(ppm)
ΔσA
(ppm)
H 362
0.5
0.4
H 687
0.1
1.1
D 362
0.07
0.08
D 687
2.0
0.5
f Al ~ 10 15%
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f bkgd 
f other ~ 1%
Ybkgd
Ytotal
f  ~ 5%
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Asymmetry (ppm)
•PassHydrogen,
687
MeV,
BLINDED
1-Raw asymmetries
2-Scaler counting correction
• Including rate, helicity-correlated corrections
Asymmetry (ppm)
Asymmetry (ppm)
Asymmetry (ppm)
Elastic Asymmetries
3-Rate correction
Octant
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4-Linear regression correction
Octant
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Asymmetries --> FFs
Unblinded, corrected asymmetries and Q2
Data
Set
Q2
(GeV2)
H362
0.221
-11.416
± 0.872
± 0.268
± 0.385
D362
0.221
-17.018
± 0.813
± 0.411
± 0.197
H687
0.628
-46.14
± 2.43
± 0.84
± 0.75
D687
0.628
-55.87
± 3.34
± 1.98
± 0.64
Aphys
(Value in ppm ± σstat ± σpt-pt ± σglobal)
Preliminary results, not for quotation
Combine with forward angle data
and nucleon EM form factors
D.S. Armstrong et al., PRL 95 (2005) 092001
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Summary of other experimental results
Q2 variation from G0 and HAPPEx at JLAB
Measurements at Q2 = 0.1 GeV2
• Mainz (A4)
• MIT-Bates (SAMPLE)
•G0 (forward)
• JLAB (HAPPEx)
GM , p 
2 u, p 1 d , p 1 s, p
GM  GM  GM
3
3
3
Combinedworld data give (at 1 ) :
GEs (Q 2  0.1 GeV 2 )   0.013  0.028
p
2
GMs (Q 2  0.1 GeV 2 )   0.62  0.31  10  5% contribution to G M(Q )
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Results
What we see:
GsE has a small positive component Q2=0.63 GeV2
GsM is consistent with zero
Comparison with theory predictions:
Lattice QCD – close to zero
some models predict small GsE and “large” GsM
First Q2 dependence of GeA(T=1)
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Comparison to Nucleon Form Factors
Recall:




2
1
GE ,, Mp  GEu ,, Mp  GEd ,,Mp  GEs ,,pM
3
3
2
1
GE ,,nM  GEd ,,Mp  GEu ,, Mp  GEs ,,pM
3
3
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June 1-19, 2015
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The G0 Collaboration
G0 Spokesperson: Doug Beck (UIUC)
California Institute of Technology, Carnegie-Mellon University, College of William and Mary,
Hendrix College, IPN Orsay, JLab, LPSC Grenoble, Louisiana Tech, New Mexico State University,
Ohio University, TRIUMF, University of Illinois, University of Kentucky, University of Manitoba,
University of Maryland, University of Winnipeg, Virginia Tech, Yerevan Physics Institute,
University of Zagreb
Analysis Coordinator: Fatiha Benmokhtar (Carnegie-Mellon,Maryland)
Thesis Students:
Stephanie Bailey (Ph.D. W&M, Jan ’07, not shown)
From left to right: Colleen Ellis (Maryland) , Alexandre Coppens (Manitoba),
Juliette Mammei (VA Tech), Carissa Capuano (W&M),
Mathew Muether (Illinois), Maud Versteegen (LPSC) , John Schaub (NMSU)
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parity violating asymmetries
elastic electron-proton scattering
strange quark
nucleon
momentum transfer
form factors
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G0 Results featured in Physical Review Focus
http://focus.aps.org
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0
G Results “published” in the Economist magazine
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