electroweak physicsd. hertzog / illinois z the gyromagnetic ratio, g, relates spin angular momentum...
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June 6, 2005 Electroweak Physics: Lecture V
Electroweak Physics
Lecture V: Survey of Low Energy Electroweak
Physics(other than neutral current interactions)
Acknowledgements:Slides from D. DeMille, G. Gratta, D. Hertzog, B.
Kayser, D. Kawall, M.J. Ramsey-Musolf
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June 6, 2005 Electroweak Physics: Lecture V
Review1. Introduction to Electroweak Physics
• Electroweak force properties; electron-positron collisions
2. Status of Electroweak Physics• Precision electroweak data from colliders
3. Electroweak Physics at low Q2
• Weak Neutral Current interactions• E158 experiment
4. Weak Neutral Current Interactions (cont’d)• Future Weak Neutral Current experiments• Strange Quarks in the Nucleon• Neutron Skin of a Lead Nucleus
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D. Hertzog / Illinois
The gyromagnetic ratio, g, relates spin angular momentum to the particle’s magnetic moment
Dirac theory: point-like, spin-1/2 particles have g = 2, but ...» proton» hyperons
» electron» muon
The muon anomalous magnetic moment is
Muon g-2
( )Sg me
Srr
2=µ
γe
γ
coupling to virtual fields
g >> 2
g almost equal to 2
( )800
122
2≈≈
−=
παµ
µg
a
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D. Hertzog / Illinois
g ≠ 2 because of virtual loops, many of which can be calculated very precisely
B
µ µγ
QED
Z
Weak
π
Had VP
π
Had LbL
11 658 470.57(29) 15.4(3) 696.3(7)
or 711.0(6)+13.0(25)
New: +50% shift !
Not agreed on yet(2003: +1.8 shift)
Others cannot …Units: x10-10
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D. Hertzog / Illinois
Precession proportional to (g-2)
INDEPENDENT of γ !
µin flight
Bat rest
Ls mceBg
ωω ==2 γ⎥⎦
⎤⎢⎣⎡
⎟⎠⎞
⎜⎝⎛ −
γ+=ωmceBg
s 221
mceBg
a ⎟⎠⎞
⎜⎝⎛ −
==2
2ωω∆
µ
θ
γ=ω
mceB
c
MOVIE
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D. Hertzog / Illinois
4 key miracles make it happenPolarized muons
Precession proportional to (g-2)
Pµ The magic momentumE field doesn’t affect muon spin when γ = 29.3
Parity violation in the decay
ν π+ µ+
µ
⎥⎦
⎤⎢⎣
⎡×⎟⎟
⎠
⎞⎜⎜⎝
⎛
−−−= EaBa
mce
avvvv β
γω µµ 1
12
cyclotronspina ωωω −=
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D. Hertzog / Illinois
aµ is proportional to the difference between the spin precession and the rotation rate
Momentum
Spin
e
mceBg
a ⎟⎠⎞
⎜⎝⎛ −
==2
2ωω∆
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D. Hertzog / Illinois
Fit to Simple 5-Par Function
0 20 40 60 80 100
Co
un
ts p
er 1
50 n
s
102
103
104
105
106
s)µtime (32 34 36 38 40
Co
un
ts p
er 1
50 n
s
0500
10001500200025003000
3x10
s)µtime (692 694 696 698
Co
un
ts p
er 1
50 n
s
020406080
100120
Few billion events
Getting a good χ2
is a challenge
N(t) = N0 e-t/τ [1+Acos(ωat + φ)]
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D. Hertzog / Illinois
Results and ImplicationsNon-zero ∆aµ appeals to a catalog of SM Extensions
New physics …SUSYLeptoquarksMuon substructureAnomalous W couplings
µ µ
W
νµ
W
B•Theory is being improved•New design to reduce error by factor of 2
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CC Weak Interaction within the SM
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June 6, 2005 Electroweak Physics: Lecture V
PV in Charged Current Processes
MCC ≈g2
8MW2 (V− A)⊗(V − A)
Fermi Constants
µ decay
β decay
GFµ
2=
g2
8MW2
GFβ
2=
g2
8MW2 Vud
GFβ GF
µ =Vud
g2 8MW2 is universal
Universality obscured by
1+∆rµ( )1+∆rβ( )
1 + ∆rβ − ∆ rµ( )
New physics
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June 6, 2005 Electroweak Physics: Lecture V
Weak decays
d → u e− ν es → u e− ν eb → u e− ν e
u c t( )Vud Vus Vub
Vcd Vcs Vcb
Vtd Vts Vtb
⎛
⎝
⎜ ⎜ ⎜
⎞
⎠
⎟ ⎟ ⎟
dsb
⎛
⎝
⎜ ⎜ ⎜
⎞
⎠
⎟ ⎟ ⎟
Vud2
+ Vus2
+ Vub2
= 1
0.9968±0.001SM
Expt
0.9487±0.001 0.0482±0.000 0.00001±0.0000
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June 6, 2005 Electroweak Physics: Lecture V
Weak decays
u c t( )Vud Vus Vub
Vcd Vcs Vcb
Vtd Vts Vtb
⎛
⎝
⎜ ⎜ ⎜
⎞
⎠
⎟ ⎟ ⎟
dsb
⎛
⎝
⎜ ⎜ ⎜
⎞
⎠
⎟ ⎟ ⎟
n→pe− ν eA(Z,N)→A(Z−1,N+1)e+ νe
π+ →π0 e+ νe
β-decay
d → u e− ν es → u e− ν eb → u e− ν e
GFβ
GFµ = Vud 1+ ∆rβ −∆rµ( )
New physics
µ−
ν µ
˜ χ 0
˜ µ −
˜ ν µ
ν e
W −
e−
ν µ
µ−
ν e
e−
˜ χ 0
˜ χ −
˜ ν µ ˜ ν e
+L
+L
SUSY
δOSUSY
OSM ~0.00
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June 6, 2005 Electroweak Physics: Lecture V
n→pe− ν eA(Z,N)→A(Z−1,N+1)e+ νe
π+ →π0 e+ νe
β-decayWeak decays
GFβ
GFµ = Vud 1+ ∆rβ −∆rµ( )
Ultra cold neutronsLANSCE: “UCN A”
Liquid N2
Be reflector
Solid D2
77 K poly
Tungsten Target
58Ni coated stainless guide
UCN Detector
Flapper valve
LHe dW ∝1+ a
r p e ⋅
r p ν
EeEν
+ Ar σ n ⋅
r p eEe
+L
Future SNS: Pulsed Cold Neutrons: “abBA”
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June 6, 2005 Electroweak Physics: Lecture V
Weak decaysn→pe− ν eA(Z,N)→A(Z−1,N+1)e+ νe
π+ →π0 e+ νe
β-decay
GFβ
GFµ = Vud 1+ ∆rβ −∆rµ( )
Ft= ft1+ ′ δ R +δNS( )1−δC( )=K 2(GF
β)2
0+ ! 0+ “Superallowed”
Nuclear structure-dependent corrections
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June 6, 2005 Electroweak Physics: Lecture V
Weak decaysn→pe− ν eA(Z,N)→A(Z−1,N+1)e+ νe
π+ →π0 e+ νe
β-decay
GFβ
GFµ = Vud 1+ ∆rβ −∆rµ( )
Ft= ft1+ ′ δ R +δNS( )1−δC( )=K 2(GF
β)2
0+ ! 0+ “Superallowed”
Nuclear structure-dependent corrections
New tests
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June 6, 2005 Electroweak Physics: Lecture V
n→pe− ν eA(Z,N)→A(Z−1,N+1)e+ νe
π+ →π0 e+ νe
β-decayWeak decays
GFβ
GFµ = Vud 1+ ∆rβ −∆rµ( )
PSI: “Pi-Beta”
Γπ+→π0e+νe( )Γπ+→µ+νµ( )~1×10−8
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June 6, 2005 Electroweak Physics: Lecture V
Weak Decays (Ongoing)
• Muon lifetime (MuLan at PSI)• Neutron lifetime (UCNA at LANSCE, NIST)• Pion Decays (PiBeta at PSI)• Kaon Decays (KLOE at INFN Frascati)• Muon Michel Parameters (TWIST at TRIUMF)
– Search for right-handed charged currents
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June 6, 2005 Electroweak Physics: Lecture V
TWIST physics motivation --test the Standard Model for µ-decay
… Most general interaction does not presuppose the W
ν
νµ±
e±
rate ~ gijγ ψ ei
Γγ ψν eψ ν µ
Γγ ψµ jγ =S,V ,Ti, j=R,L
∑
2
• S,V,T = scalar, vector or tensor interactions
• R, L = right and left handed leptons (e, µ, or τ )
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June 6, 2005 Electroweak Physics: Lecture V
rate ~ gijγ ψ ei
Γγ ψν eψ ν µ
Γγ ψµ jγ =S,V ,Ti, j=R,L
∑
2Couplings in the present Standard Model
gRRS = 0
gLRS = 0
gRLS = 0
gLLS = 0
gRRV = 0
gLRV = 0
gRLV = 0
gLLV =1
gRRT ≡ 0
gLRT = 0
gRLT = 0
gLLT ≡ 0
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June 6, 2005 Electroweak Physics: Lecture V
e+ spectrum in x, cosθe
rate ~ x2 3 − 3x +23
ρ 4 x − 3( )+ 3ηxo1− x
x⎛ ⎝ ⎜
⎞ ⎠ ⎟ + Pµξ cosθe 1− x +
23
δ 4x − 3( )⎛ ⎝ ⎜
⎞ ⎠ ⎟
⎡
⎣ ⎢ ⎤
⎦ ⎥
x ≡Ee
Eemax
Spectral shape in x, cosθe is characterized in terms of four parameters -- ρ, η , ξ, δ
θe r p e
r s µ
Pµ is the muon polarization
xo ≡me
Eemax
Eemax ≡
mµ2 + me
2
2mµ(L. Michel, A. Sirlin)
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June 6, 2005 Electroweak Physics: Lecture V
ρδξη
Pµξδρ
TWIST at TRIUMFTWIST at TRIUMF
SM3/4 3 /4 1.0 0.0 1.0
TWIST will measure ρ, ξ, δ in two steps --10-3 in 2004; ~3x10-4 in 2005/6
TWIST will measure ρ, ξ, δ in two steps --10-3 in 2004; ~3x10-4 in 2005/6
Highly polarized µ+
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June 6, 2005 Electroweak Physics: Lecture V
Discrete Symmetries
• P, C and CP violated• CPT likely conserved (being tested)• Therefore, T violation expected• Baryon number violation
– Proton decay?• Lepton Number Violation
– Neutrino mass and mixing– Charge lepton number violation?
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June 6, 2005 Electroweak Physics: Lecture V
P T
D S
3
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June 6, 2005 Electroweak Physics: Lecture V
ee
γx
P and CP-violating processes
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June 6, 2005 Electroweak Physics: Lecture V
Electric dipole moment (EDM) searches may test new CP-violation
f dSM dexp dfuture
e−
n199Hg
µ
< 10−40
< 10−30
< 10−33
< 10−38
< 1.6 ×10−27
< 6.3 ×10−26
< 2.1×10−28
< 1.1×10−18
→ 10−31
→ 10−29
→ 10−32
→ 10−24
If new CP violation is responsible for abundance of matter, will these experiments see an EDM?
CKM
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June 6, 2005 Electroweak Physics: Lecture V
Proton Decay & Neutrino Mass
• Small amount of baryon number violation expected
• Does the proton decay?• Is the solar neutrino flux as expected?• Birth of Underground Science!• We now know neutrinos have mass• We now understand the dynamics of
hydrogen burning in the sun to ~1%…
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June 6, 2005 Electroweak Physics: Lecture V
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June 6, 2005 Electroweak Physics: Lecture V
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June 6, 2005 Electroweak Physics: Lecture V
Dirac or Majorana neutrinos?
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June 6, 2005 Electroweak Physics: Lecture V
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June 6, 2005 Electroweak Physics: Lecture V
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June 6, 2005 Electroweak Physics: Lecture V
Double Beta Decay
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June 6, 2005 Electroweak Physics: Lecture V
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June 6, 2005 Electroweak Physics: Lecture V
Future Underground Science
• Precision solar neutrino spectra• Neutrino MNS matrix parameters
– CP Violation?• Proton Decay• Double Beta Decay• …
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• Capture on Nucleus: µ-N(Z,A) νµN(Z-1,A)• Decay in Orbit: µ- νµe-νe (DIO)
When a muon stops in matter, the principal interactions are:Lepton Flavor Violation
Coherent conversion is µ-N(Z,A) e-N(Z,A), and the signalis a monoenergetic electron beyond the DIO endpoint.
The MECO experiment at BNL will measure: Rµe= Γ[µ-N(Z,A) e-N(Z,A)]/ Γ[µ-N(Z,A) νµN(Z-1,A)]
A single event implies Rµe > 2 X 10-17.
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New Physics at High Energy Scales
µ- e-
q q
χi0~
lj lj~~
q
µ-
q
e-
Supersymmetry CompositenessPredictions at 10-15 =CΛ 3000 TeV
µ- e-
q q
N
WHeavy Neutrinos µ- e-
q q
He-
t
t tHiggs
µ- e-
q q
γ,Z,Z’
µ′
−
=
→ <
2Z
17
M 3000 TeV/cB(Z ) 10e
Heavy Z’, Anomalous Z coupling
µ- d
d e-
L
After W. Marciano
Leptoquarks
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Features of the MECO Experiment• 1000–fold increase in µ beam intensity over existing facilities
– High Z target for improved pion production– Axially-graded 5 T solenoidal field to maximize pion capture
• Curved transport selects low momentum µ−
• Muon stopping target in a 2 T axially-graded field to improve conversion e- acceptance
• High rate capability electron detectors in a constant 1 T field
CalorimeterStraw Tracker
Stopping Target Foils
Pion Production Target
Superconducting Solenoids
Proton Beam
MuonBeam
5 T2.5 T
2 T
1 T
1 T
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MECO Detector Elements
Magnetic spectrometer measures electron momentum with precision of 0.3% (rms)—essentialto eliminate decay in orbit background. Consists of ~2800 axial straw tube detectors 2.6 m x5 mm. 25 µm wall thickness.
~1200 element PbWO4 (3.5 x 3.5 x 12 cm) calorimeter measures electron energy to ~5%,providing trigger and confirming trajectory.
Electron starts here.
Position resolution: 0.2 mm transversely,1.5 mm axially
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June 6, 2005 Electroweak Physics: Lecture V
Summary
• An extraordinary amount has been learnt about electroweak physics in the past fifty years
• Further progress requires a coherent effort across High Energy Physics, Nuclear Physics and Particle Astrophysics
• Accelerator- and non-accelerator experiments will play equally important roles
• Together, we will finally address some of the outstanding questions unanswered by the current version of the electroweak theory
• Your generation can help towards generating the required unity and coherence