B. Lee Roberts ISS Plenary Meeting: RAL 26 April 2006 - p. 1/39 Muon Physics at the Front End of a Factory An introduction B. Lee Roberts Boston University

B. Lee Roberts ISS Plenary Meeting: RAL 26 April 2006 - p. 1/39

Muon Physics at the Front End of a FactoryAn introduction

B. Lee RobertsBoston University

with some theory projections taken fromYasuhiro Okada

KEK

roberts @ bu.edu http://physics.bu.edu/roberts/html


Outline

• Introduction to the muon

• GF

• Lepton Flavor Violation

• Magnetic and electric dipole moments

• Summary and conclusions.


The Muon (“Who ordered that?”)

• Lifetime ~2.2 s, practically forever• 2nd generation lepton

• mme = 206.768 277(24)

• produced polarized– in-flight decay: both “forward” and “backward” muons qre highly

polarized

• Paul Scherrer Institut has 108 /s in a beam


What can we learn from the ’s death?

• The strength of the weak interaction– i.e. the Fermi constant GF

• The fundamental nature of the low-energy weak interaction– i.e. is it scalar, vector, tensor, pseudo-scalar,

pseudo-vector or pseudo-tensor?


helped predict the mass of the top quark

Predictive power in weak sector of SM. Difference between the charged current and neutral current propagators The radiative correction shown above depends on mt

2. Comparisons of charged, vrs. neutral currents gives information on mt.


The Electro-Weak Working Group Fits:

Predicted

Input: GF (17 ppm), (4 ppb at q2=0), MZ (23 ppm),

Measured:

from

GF

The Lan experiment at PSI will accumulate 1012 -decays and measure GF to ~1 ppm. If LHC provides a Higgs Mass, then the precision of the confrontation with the SM will greatly improve


The Muon Trio: LFV, MDM, EDM• Lepton Flavor Violation

• The standard-model gauge bosons do not permit leptons to mix, but new physics at the TeV scale such as SUSY does.


SUSY GUT and SUSY Seesaw model

The flavor off-diagonal terms in the slepton mass matrix are induced by renormalization effects due to GUT and/or neutrino interactions.

LFV

@ Mplanck

GUT Yukawa interaction Neutrino Yukawa

interaction

CKM matrix Neutrino oscillation

L.J.Hall,V.Kostelecky,S.Raby,1986;A.Masiero, F.Borzumati, 1986


Many models beyond the S-M contain sources of LFV• Although the simple seesaw or Dirac neutrino

model predicts too small generate branching ratios for the charged lepton LFV, other models of neutrino mass generation can induce observable effects.

• For example:– Generalized Zee model (K.Hasagawa, C.S.Lim, K.Ogure,

2003)– Neutrino mass from the warped extra dimension

(R.Kitano,2000)– R-parity violating SUSY model (A.de

Gouvea,S.Lola,K.Tobe,2001)– Triplet Higgs model (E.J.Chun, K.Y.Lee,S.C.Park;

N.Kakizaki,Y.Ogura, F.Shima, 2003) – Left-right symmetric model (V.Cirigliano, A.Kurylov,

M.J.Ramsey-Musolf, P.Vogel, 2004) – SUSY seesaw model (F.Borzumati and A.Masiero 1986)


Experimental bounds

Process Current Future

(Ti)

→ e conversion search at the level of 10-18 is proposedin the future muon facility at J-PARC (PRIME).


Past and Future of LFV Limits

+e-→-e+

Bra

nchi

ng R

atio

Lim

it


→ e branching ratio (typical example)

SU(5) and SO(10) SUSY GUT

SUSY seesaw model

The branching ratio can be largein particular for SO(10) SUSY GUT model.

J.Hisano and D.Nomura,2000

K.Okumura

SO(10)

SU(5)

Right-handed neutrino mass

Right-handed selectron mass

MEGA


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.


Comparison of three muon processes in various new physics models

SUSY GUT/Seesaw

B(→e ) >> B(→3e) ~ B(A→eA)

Various asymmetries in polarized decays.SUSY with large tan

→e conv. can be enhanced. Z-dependence in →e conv. branching ratio.

Triplet Higgs for neutrino

B(→3e) > or ~ B(→eg) ~B(A→eA)

RL model B(→3e) >> B(→eg) ~B(A→eA)

Asymmetry in →3e

RPV SUSY Various patterns of branching ratios and asymmetries

want to measure all three LFV processes to disentangle the models


The First -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 any flavor conservation, the expected branching fraction for +e+ is about 10-5.

• Steinberger and Wolf first looked for -N e-N, publishing a null result in 1955, Re < 2 10-4

Absorbs e- from -

decay

Conversion e- reach this

counter

9”


Z dependence of mu-e conversion branching ratio

have calculated the coherent mu-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

R.Kitano, M.Koike and Y.Okada. 2002


The branching ratio is largestfor the atomic number of Z=30 – 60.

For light nuclei, Z dependencesare similar for different operator forms.

Sizable difference of Z dependences for dipole, scalar and vector interactions. This is due to a relativistic effect of the muon wave function.

-e conversion rate normalized to Al

dipole scalar vectorproviding another way to discriminate different models

Kitano, Koike, Okada


The Muon Trio: MDM, EDM

• Muon MDM (g-2) chiral changing

• Muon EDM


Electric and Magnetic Dipole Moments

Transformation properties:

An EDM implies both P and T are violated. An EDM at a measureable level would imply non-standard model CP. The baryon/antibaryon asymmetry in the universe, needs new sources of CP.


SUSY connection between a , Dμ , μ → e

→ e MDM, EDM

~ ~


Magnetic Dipole moments

• Field invented by Otto Stern in 1921


(in modern language)


Dirac + Pauli moment


Non-Standard Model Value for Muon (g-2) ?

e vrs. : relative contribution of heavier things

?S


aμ is sensitive to a wide range of new physics

• substructure

• SUSY (with large tanβ )

• many other things (extra dimensions, etc.)


The hadronic contribution to ahas to come from data


E821 achieved 0.5 ppm and the e+e- based theory is also at the 0.6 ppm level. Both can be improved.

All E821 results were obtained with a “blind” analysis.

world average


Based on the latest report on e+e- → hadrons there is an apparent discrepancy at the level of 2.9 . . .

• A new experiment at BNL (E969) could improve the confrontation with theory by a factor of 2

• What implications might the possible (g-2) discrepancy have for muon physics at a neutrino factory?– New physics at the TeV scale?

• Could one do 10 times better?• A few words about the technique which is

important to understand for the EDM experiment


We measure the difference frequency between the spin and momentum precession

0With an electric quadrupole field for vertical focusing


The 700 ton (g-2) precision storage ring

Muon lifetime t = 64.4 s

(g-2) period ta = 4.37 s

Cyclotron period tC = 149 ns

Scraping time (E821) 7 to 15 s

Total counting time ~700 s

Total number of turns ~4000


The magnetic field is measured and controlled using pulsed NMR, and the muon spin precession is measured using →e decay


(g-2) ten times better (0.05 ppm) ?

• Need to know to 0.01 ppm (10 ppb)

• Need ~1014 polarized muons at ≥ 3 GeV/c momentum

• Need substantial improvements in theory for the result to be interpreted


Present EDM Limits

Particle Present EDM limit

(e-cm)

SM value

(e-cm)

n

future exp 10-24 to 10-25

*projected


Naïve scaling would imply that

but in some models the dependence is greater, e.g.


μ EDM may be enhancedabove mμ/me × e EDM

Magnitude increases withmagnitude of ν Yukawa couplings

and tan β

μ EDM greatly enhanced when heavy neutrinos non-degenerate

Model Calculations of EDM


aμ implications for the muon EDM


Spin Frequencies: in B field with MDM & EDM

The EDM causes the spin to precess out of plane.

The motional E - field, β X B, is much stronger than laboratory electric fields.

spin difference frequency = s - c

0


Dedicated EDM Experiment

With a = 0, the EDM causes the spin to steadily precess out of the plane.

0

Use a radial E-field to turn off the a precession


In the next talk, Klaus Jungmann will give a few more details on a dedicated muon EDM experiment.


Summary and Conclusions

• There are a number of interesting topics which can be pursued at a high intensity muon source– Lepton Flavor Violation– Search for a permanent EDM of the muon

are the most compelling

• The next talk will cover these topics in more detail


Extra Projections


The error budget for E969 represents a continuation of improvements already made during E821

• Field improvements: better trolley calibrations, better tracking of the field with time, temperature stability of room, improvements in the hardware

• Precession improvements will involve new scraping scheme, lower thresholds, more complete digitization periods, better energy calibration

Systematic uncertainty (ppm) 1998 1999 2000 2001 E969

Goal

Magnetic field – p 0.5 0.4 0.24 0.17 0.1

Anomalous precession – a 0.8 0.3 0.31 0.21 0.1

Statistical uncertainty (ppm) 4.9 1.3 0.62 0.66 0.14

Total Uncertainty (ppm) 5.0 1.3 0.73 0.72 0.20



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B. Lee Roberts ISS Plenary Meeting: RAL 26 April 2006 - p. 1/39 Muon Physics at the Front End of a Factory An introduction B. Lee Roberts Boston University