Transcript Slide 1

Muon Physics at the Front-end of a
Neutrino Factory
First published muon
observation: Paul Kunze,
Z. Phys. 83, 1 (1933)
“a particle of uncertain nature”
Lee Roberts
Department of Physics
Boston University
roberts @bu.edu
http://g2pc1.bu.edu/~roberts
B.
Lee Roberts, NuFact2008 – 4 July 2008
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m
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Outline
• Introduction to the muon
• The Muon Trio:
– The Magnetic
dipole moment: am ,
– The Electric Dipole Moment dm
– Lepton Flavor Violation
• Other Muon Experiments
• Summary and conclusions.
Some slides/figures have been borrowed from:
Klaus Jungmann, Dave Hertzog, Klaus Kirch
Jim Miller, Yasuhiro Okada and Andries van der Schaaf
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Muon properties:
• Born Polarized
• Decay is self-analyzing
High-energy e± carry
muon spin information!
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What has the muon done for us (besides being
associated with the production of
or
) ?
• The strength of the weak interaction
– i.e. the Fermi constant GF (more properly Gm)
• The V - A nature of the weak interaction
• Lepton flavor conservation in m-decay
(thus far)
• VEV of the Higgs field:
• Induced form-factors in nuclear m-capture
– complementary to b-decay
• Constraints on new physics from am,
– constrains many models of new physics
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Theory of Magnetic and
Electric Dipole Moments
Proc. R. Soc. (London) A117, 610 (1928)
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Magnetic and Electric Dipole Moments
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The magnetic dipole moment directed along spin.
Dirac Theory: gs = 2
Dirac + Pauli moment
For leptons, radiative
corrections dominate the
value of
a
≃ 0.00116…
Bottom line: Anomalous moment
represents a sum rule over all physics, not
just the known physics.
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B. Lee Roberts, NuFact2008 – 4 July 2008
Modern Notation:
• Muon Magnetic Dipole Momoment am chiral changing
• Muon EDM
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The SM Value for the muon anomaly (10-10)
10 (2)
New BaBar e+e- → p p results expected in September
Eduardo de Rafael:
Theory of the muon anomalous
magnetic moment
P and T violation at low energies,
Heidelberg, Jun - 2008
11 659 178.3 (4.8)
# from Miller, de Rafael, Roberts, Rep. Prog. Phys. 70 (2007) 795–881
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aμ is sensitive to a wide range of new physics
• e.g. SUSY (with large tanβ )
• many other things (extra dimensions, etc.)
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Spin Motion in a
Magnetic Field
wC - cyclotron frequency
wS - spin frequency
wa - spin turns relative to the momentum
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0
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As
spin precesses,
the number of high E electrons
Figure
of merit:
oscillates with frequency wa.
(MDM or EDM)
Count number of e- with
Ethresh ≥ 1.8 GeV
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We count high-energy electrons as a
function of time.
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E821 achieved 0.5 ppm and the e+e- based theory is
also at the 0.6 ppm level. Difference is 3.7
3.4ss
MdRR=Miller, de Rafael,
Roberts, Rep. Prog.
Phys. 70 (2007) 795
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The Snowmass Points and Slopes give benchmarks to test
observables with model predictions
Muon g-2 is a powerful discriminator ...
no matter where the final value lands!
Expt
Present
Future?
Model Version
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Complementary to LHC data: e.g.
am provides the best measure of m and tan b
MSSM reference point SPS1a
With these SUSY parameters, LHC
gets tan b of 10.22 ± 9.1.
See:
arXiv:0705.4617v1 [hep-ph]
with improvements in theory and
experiment things can improve to:
m > 0 by > 6 s
tan b to < 20%
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The search for a Muon
Electric Dipole Moment
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Purcell and Ramsey: EDM would violate Parity
Proposed to search for an EDM of the neutron
“raises directly the question of parity.”
Phys. Rev. 78 (1950)
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Electric Dipole Moment:
P T
Transformation
Properties
If CPT is valid, an EDM would imply non-standard
model CP.
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The present EDM limits are orders of magnitude
from the standard-model value
Particle
Present EDM limit
SM value
(e-cm)
(e-cm)
n
199Hg
The discovery of a permanent EDM would change
our picture of nature at least as profoundly as the
discovery of neutrino mass has!
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e EDM (e.cm)
Excluded region
(Tl atomic beam)
Commins (2002)
10-22
10-24
10-26
n
-28 Hg
10199
Multi
Higgs
MSSM
f~1
Left MSSM
Right
f ~ a/p
10-30
10-32
10-34
10-36
de < 1.6 x 10-27 e.cm
The SUSY CP
E. Hinds’ e-EDM
experiment
at Imperial College
with YbF molecules
problem! is starting
to explore this region
The strong CP problem!
Standard Model
with thanks to Ed Hinds
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aμ (new physics) implications for dm
Either dµ is of order 10–22 e cm, or the CP phase is strongly suppressed!
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Model Calculations of m EDM
μ EDM may be enhanced
above mμ/me × e EDM
Magnitude increases with
magnitude of n Yukawa couplings
and tan β
μ EDM greatly enhanced
when heavy neutrinos non-degenerate
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Spin Frequencies: m in B field with MDM & EDM
0
The motional E - field,
β X B, is (~GV/m).
The EDM causes the
spin to precess out
of plane.
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Total frequency
w
wa
wh
Plane of the spin precession
tipped by the angle d
Number above (+) and below (-) the midplane will vary as:
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E821 looked for this vertical oscillation in 3 ways
• No significant oscillation was found
• The observed Dam is not from an EDM at the
2.2 s level
• One can improve significantly at a neutrino
factory, since an EDM limit of 10-23 e·cm
needs NP 2 = 1016
Bottom line: Muon EDM measurement
needs the high intensity that could be
available at a neutrino factory.
Also *need
modified
technique!
Coming
soon to a preprint
server near you
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Dedicated EDM Experiment
0
Use a radial E-field to turn off the wa precession
“Frozen spin”
With wa = 0, the EDM causes the spin to steadily
precess out of the plane.
wh
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“Frozen spin” technique to measure EDM
•
•
•
•
Turn off the (g-2) precession with radial E
Up-Down detectors measure EDM asymmetry
Look for an up-down asymmetry building up with time
Side detectors measure (g-2) precession
– To prove the spin is frozen
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PSI suggestion: Adelmann and Kirch
hep-ex/0606034
A. Adelmann1, K. Kirch1, C.J.G. Onderwater2, T. Schietinger1, A. Streun1
1PSI, 2KVI
(by A. Streun)
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Muon EDM Limits: Present and Future
E821: G. Bennett, et al.,
(Muon g-2 collaboration)
to be submitted to PRD
2008
E821
? new (g-2)
Need:
NA 2 = 1016 for
dm ≃ 10-23 e·cm
NuFact
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SUSY connection between MDM, EDM and the
lepton flavor violating transition moment m → e
SUSY
slepton mixing
m→e
MDM, EDM
~
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~
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10-3
Branching Ratio Limit
Lepton
Flavor
Violation
10-1
10-5
m+ e-→m -e+
10-7
10-9
10-11
¹ + ! e+ ° 2-body
10 final state
1940 1950 1960 1970 1980 1990 2000
¹ + ! e+ e¡ e+
¹ ¡ + N ! e¡ + N mono-energetic electron
( ¹ + e¡ ) ! ( ¹ ¡ e+ )
-13
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Experimental bounds
Process
Current
(Ti)
Future
10-16 m2e
10-16 Comet
Under some assumptions the DLf = 1 rates are related
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Presently active: m + → e+ g (MEG @ PSI)
• First running is going on now
– goal < 10-13
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Muonic Atom: m- bound in hydrogen-like atomic orbit
1s
2p
2s
r
Balmer
series
Lyman
series
coherent process
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me
-
conversion operators
R.Kitano, M.Koike and Y.Okada. 2002
have calculated the coherent m-e conversion branching ratios in
various nuclei for general LFV interactions to see:
(1) which nucleus is the most sensitive to mu-e conversion searches,
(2) whether one can distinguish various theoretical models by the Z
dependence.
Relevant quark level interactions
Dipole
Scalar
Vector
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m-e conversion rate normalized to Al
The branching ratio is largest
for the atomic number of
Z = 30 – 60.
For light nuclei, Z
dependences
similar for different operators
Sizable difference of Z
dependences for dipole,
scalar and vector
interactions (relativistic
effect of Ym).
Kitano, Koike, Okada
Bottom line: If you can observe muonelectron conversion, a study of the Z
scalar
vector
dependence mightdipole
help sort
out which
providing another way to discriminate different models
operators contribute.
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B. Lee Roberts, NuFact2008 – 4 July 2008
The First m-N  e-N Experiment Steinberger and Wolf
• After the discovery of the muon it was realized it could decay into an
electron and a photon, or convert to an electron in the field of a nucleus.
• Without lepton flavor conservation, the expected branching fraction for
m+  e+g is about 10-5
•
Steinberger and Wolf
m-N  e-N, (1955)
R < 2  10-4
me
m  + ( A, Z )  e + ( A, Z )
R
m  + ( A, Z ) n m + X
Absorbs efrom mdecay
9”
Conversion
e- reach this
counter
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Two New Proposals for m to e Conversion Experiments
•
m2e at Fermilab
– based on MECO / MELC proposals
• COMET at J-PARC
-to be upgraded to
SINDRUM II @PSI
Data and
simulation
PRISM/PRIME
prompts suppressed
decay in orbit
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(simulated)
signal
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The
m2e Apparatus proposed for Fermilab
Phase 1: 90% C.L. limit of Rme< 6 x 10-17
Phase 2:Pions
90% C.L.Proton
limit of RmeTarget
≲ 10-18
Target Shielding
Superconducting
(Copper)
Protons
Transport Solenoid
p beam
(2.5 T – 2.1
T)
enter
here
Crystal
Calorimeter
Straw Tracker
B=5T
Target
Superconducting
Shielding
Production Solenoid
(5.0 T – 2.5 T)
(Tungsten)
B=2.5T
Muons
Collimators
Muon Stopping
Target
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Superconducting
Detector Solenoid
(2.0 T – 1.0 T)
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COMET Proposal @ J-PARC
me conversion
90% CL Rme < 10-16
curved detector to reduce low E
DIO background
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Rme < 10-18
Bottom line: FFAG reduces Dp of the muon
beam by phase rotation:
narrow Dt → narrow Dp ⇒ thinner stopping
target
better e- resolution and eliminates the pions
which can cause ZN (p ,g) background!
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Muonium to Anti-muonium Conversion
Predicted
M-M
Conversion
1957Named
System
“Muonium” ?
Flavor oscillations well established in quark
sector
L. Willmann,
et al., PRL 82, 49 (1999)
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L. Willmann, et al., PRL 82,
49 (1999) (done @PSI)
90% CL:
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Future Efforts at Existing Facilities
• (g-2)m
– FNAL ?
– J-PARC ?
• MEG
– running now!
• m2e
– proposal being prepared for Fermilab
• COMET/ PRISM/PRIME
– proposed
to The
J-PARC,
future under
discussionfor me
Bottom
line:
ultimate
sensitivity
conversion could be reached at the front
end of a neutrino factory. The discovery of
LFV would also significantly change our
view of the world.
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B. Lee Roberts, NuFact2008 – 4 July 2008
Summary
• Muon physics has provided much information
in the development of the standard model,
including a hint of new physics in am.
• The electric dipole moment could be measured
to a competitive level (to e-) at a neutrino
factory.
• Muon flavor violation can be pursued to the
ultimate sensitivity, or studied systematically
at a neutrino factory.
• The observation of either of these SM
“forbidden” effects would be incredibly
important in reshaping our view of nature.
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Extra Projections
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Comparison of three processes
If the photon penguin process dominates, there are simple relations among
these branching ratios.
This is true in many, but not all SUSY modes.
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PSI suggestion:
A. Adelmann1, K. Kirch1, C.J.G. Onderwater2, T. Schietinger1, A. Streun1
hep-ex/0606034
B=1T
pm = 125 MeV/c
bm = 0.77, gm = 1.57
In 1 year of running @ PSI
P ≈ 0.9
E = 0.64 MV/m
R = 0.35 m
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Comparison of three muon processes in various new physics
models
SUSY
GUT/Seesaw
B( m→e g ) >> B(m→3e) ~
SUSY with
large tan b
m→e conversion can be enhanced. Z-dependence in
m→e conversion BR.
Triplet Higgs
for neutrino
B(m→3e) > or ~ B(m→eg) ~B(mN→eN)
RL model
B(m→3e) >> B(m→eg) ~B(mN→eN)
Asymmetry in m→3e
RPV SUSY
Various patterns of branching ratios and
asymmetries
B(mN→eN)
Various asymmetries in polarized m decays.
want to measure all three LFV processes to disentangle the models
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me Conversion is sensitive to a wide range
of new physics
Supersymmetry
Compositeness
Predictions at 10-15
ΛC = 3000 TeV
Second Higgs
doublet
Heavy Neutrinos
2
*
UμN
UeN = 8×10-13
gHμe =10-4 ×gHμμ
Heavy Z’,
Anomalous Z
coupling
Leptoquarks
ML =
MZ = 3000 TeV/c 2
3000 λμd λed TeV/c 2
After W. Marciano
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B(Z  μe) < 10-17
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m+ → e+ g branching ratio (typical example)
SUSY seesaw model
J.Hisano and D.Nomura,2000
SU(5) and SO(10) SUSY GUT
K.Okumura
MEGA
SO(10)
MEG
SU(5)
Right-handed selectron mass
The branching ratio can be large
in particular for SO(10) SUSY GUT model.
Right-handed neutrino mass
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