Lepton Flavor Violation: Goals and Status of the MEG Experiment at PSI Stefan Ritt Paul Scherrer...

Lepton Flavor Violation:Goals and Status of the MEG

Experiment at PSI

Stefan RittPaul Scherrer Institute, Switzerland

26 June '07 Particle Colloquium Heidelberg 2

Agenda

Search for e down to 10-13

• Motivation

• Experimental Method

• Status and Outlook

Motivation

Why should we search for e ?


The Standard Model

Fermions (Matter)

Quarks

uup

ccharm

ttop

ddown

sstrange

bbottom

Lepto

ns

eelectronneutrino

muon

neutrino

tau

neutrino

eelectron

muon

tau

Bosons

photon

Force

carrie

rs

ggluon

WW boson

ZZ boson

Higgs*

boson

*) Yet to be confirmedGeneration I II III


The success of the SM

• The SM has been proven to be extremely successful since 1970’s

• Simplicity (6 quarks explain >40 mesons and baryons)

• Explains all interactions in current accelerator particle physics

• Predicted many particles (most prominent W, Z )

• Limitations of the SM

• Currently contains 19 (+10) free parameters such as particle (neutrino) masses

• Does not explain cosmological observation such as Dark Matter and Matter/Antimatter Asymmetry

CDF

Today’s goal is to look for physics beyond the standard

model

Today’s goal is to look for physics beyond the standard

model


Beyond the SM

Find New PhysicsBeyond the SM

High Energy Frontier

• Produce heavy new particles directly• Heavy particles need large colliders• Complex detectors

High Precision Frontier

• Look for small deviations from SM (g-2) , CKM unitarity

• Look for forbidden decays• Requires high precision at low energy


Neutron beta decay

Neutron decay via intermediate heavy W- boson

ddu

udu

pn

W -e-

e

n p+ + e - + e

~80 MeV

~5 MeV

Neutron mean life

time:

886 s

Neutron mean life

time:

886 s

decay discovery:

~1934

W- discovery:

1983

decay discovery:

~1934

W- discovery:

1983


New physics in decay

Can’t we do the same in decay?

e-??

Probe physics at TeV scale with high precision decay measurement Probe physics at TeV scale with high precision decay measurement


•Discovery: 1936 in cosmic radiation

•Mass: 105 MeV/c2

•Mean lifetime: 2.2 s

The MuonSeth Neddermeyer

Carl Anderson

e

-

W-e-

e

e

e

e

e ≈ 100%

0.014

< 10-11

led to Lepton Flavor Conservationas “accidental” symmetry


Lepton Flavor Conservation

• Absence of processes such as e led to concept of lepton flavor conservation

• Similar to baryon number (proton decay) and lepton number conservation

• These symmetries are “accidental” because there is no general principle that imposes them – they just “happen” to be in the SM (unlike charge and energy conservation)

• The discovery of the failure of such a symmetry could shed new light on particle physics


LFV and Neutrino Oscillations

Neutrino Oscillations Neutrino mass e possible even in the SM

W-

ee-

SM

604

4B 10R( )

W

em

m

LFV in the charged sector is forbidden in the Standard Model

LFV in the charged sector is forbidden in the Standard Model

mixing


LFV in SUSY

• While LFV is forbidden in SM, it is possible in SUSY

W-

ee-

e-0~

~e~

SM

604

4B 10R( )

W

em

m

SUSYBR( )e

4

5 2

SUS2

Y

2100 GeV

10 tanem

mm

≈ 10-12

Current experimental limit: BR( e ) < 10-11Current experimental limit: BR( e ) < 10-11

2~~em


• LFV is forbidden in the SM, but possible in SUSY (and many other extensions to the SM) though loop diagrams ( heavy virtual SUSY particles)

• If e is found, new physics beyond the SM is found

• Current exp. limit is 10-11, predictions are around 10-12 … 10-14

• First goal of MEG: 10-13

• Later maybe push to 10-14 ($$$)

• Big experimental challenge

• Solid angle * efficiency (e,) ~ 3-4 %

• 107 – 108 /s DC beam needed

• ~ 2 years measurement time

• excellent background suppression

LFV Summary


History of LFV searches

• Long history dating back to 1947!

• Best present limits:

• 1.2 x 10-11 (MEGA)

• Ti → eTi < 7 x 10-13 (SINDRUM II)

• → eee < 1 x 10-12 (SINDRUM II)

• MEG Experiment aims at 10-13

• Improvements linked to advancein technology

1940 1950 1960 1970 1980 1990 2000 2010

10-1

10-2

10-3

10-4

10-5

10-6

10-7

10-6

10-9

10-10

10-11

10-12

10-13

10-14

10-15

→ e → eA → eee

MEG

SUSY SU(5)

BR( e ) = 10-13

Ti eTi = 4x10-16

BR( eee) = 6x10-16

SUSY SU(5)

BR( e ) = 10-13

Ti eTi = 4x10-16

BR( eee) = 6x10-16

cosmic

stopped

beams

stopped


Current SUSY predictions

“Supersymmetric parameterspace accessible by

LHC”

“Supersymmetric parameterspace accessible by

LHC”

W. Buchmueller, DESY, priv. comm.

current limit

MEG goal

1) J. Hisano et al., Phys. Lett. B391 (1997) 3412) MEGA collaboration, hep-ex/9905013

ft(M)=2.4 >0 Ml=50GeV 1)

tan


LFV link to other SUSY proc.

e-0~

~e~

2~~em

0~

~

2~~m

e-LFVe-LFV

gg

~

0~

~

2~~m

~

EDMEDM

2~~

2~~

2~~

2~~

2~~

2~~

2~~

2~~

2~~

mmm

mmm

mmm

te

e

eeee

slepton mixing matrix:

1227 10

)(sin3.1

10

eBR

cme

de

In SO(10), eEDM is related to e

In SO(10), eEDM is related to e

R. Barbieri et al., hep-ph/9501334

Experimental Method

How to detect e ?


Decay topology e

e

e

180º

→ e signal very clean• Eg = Ee = 52.8 MeV• e = 180º• e and in time

52.8 MeV

52.8 MeV

10 20 30 40 50 60 E[MeV]

N

52.8 MeV

10 20 30 40 50 60 Ee[MeV]

N

52.8 MeV


Michel Decay (~100%)

Three body decay: wide energy spectrum

e

e

Ee[MeV]

N 52.8 MeV

Ee[MeV]

N 52.8 MeV

TheoreticalTheoretical

Convoluted withdetector resolution

Convoluted withdetector resolution


Radiative Muon Decay (1.4%)

e

e

E[MeV]

N 52.8 MeV

“Prompt” Background“Prompt” Background


“Accidental” Background

e

e

180º

→ e signal very clean• Eg = Ee = 52.8 MeV• e = 180º• e and in time

e

e

e

e

Annihilationin flight

Background

Good energy resolutionGood spatial resolution

Excellent timing resolutionGood pile-up rejection


Previous Experiments

Exp./Lab

Author Year Ee/Ee

%FWHM

E/E

%FWHM

te

(ns)

e

(mrad)

Inst. Stop rate (s-1)

Duty cycle (%)

Result

SIN (PSI)

A. Van der Schaaf

1977 8.7 9.3 1.4 - (4..6) x 105 100 < 1.0 10-9

TRIUMFP.

Depommier1977 10 8.7 6.7 - 2 x 105 100 < 3.6 10-9

LANLW.W.

Kinnison1979 8.8 8 1.9 37 2.4 x 105 6.4 < 1.7 10-10

Crystal Box

R.D. Bolton 1986 8 8 1.3 87 4 x 105 (6..9) < 4.9 10-11

MEGA M.L. Brooks 1999 1.2 4.5 1.6 17 2.5 x 108 (6..7) < 1.2 10-11

MEG ? ? ? ? ? ? ~ 10-13

How can we achieve a quantum step in detector technology?How can we achieve a quantum step in detector technology?


How to build a good experiment?


Collaboration

~70 People (40 FTEs) from five countries


Paul Scherrer Institute

Swiss Light Source

Proton Accelerator


PSI Proton Accelerator


Generating muonsCarbon Target

590 MeV/c2 Protons1.8 mA = 1016 p+/s

+

+

+

+

108 +/s


Muon Beam Structure

Muon beam structure differs for different accelerators

Pulsed muon beam, LANL

Duty cycle: Ratio of pulse width over period

DC muon beam, PSI

Duty cycle: Ratio of pulse width over period

Duty cycle: 6 % Duty cycle: 100 %

Instantaneous rate much higher in pulsed beamInstantaneous rate much higher in pulsed beam


Muon Beam Line

Transport 108 +/s to stopping target inside detector with minimal background

+ from production target

x

x

x x

x x+

e+

-

+

0)(!

BvEqF

Lorentz Force vanishes for given v:Lorentz Force vanishes for given v:

Wien FilterWien Filter


Results of beam line optimization

+

R ~ 1.1x108 +/s at experiment

~ 10.9 mm ~ 10.9 mm

e+

+


Previous Experiments

Exp./Lab

Author Year Ee/Ee

%FWHM

E/E

%FWHM

te

(ns)

e

(mrad)


Duty cycle (%)

Result

SIN (PSI)

A. Van der Schaaf

1977 8.7 9.3 1.4 - (4..6) x 105 100 < 1.0 10-9

TRIUMFP.

Depommier1977 10 8.7 6.7 - 2 x 105 100 < 3.6 10-9

LANLW.W.

Kinnison1979 8.8 8 1.9 37 2.4 x 105 6.4 < 1.7 10-10

Crystal Box

R.D. Bolton 1986 8 8 1.3 87 4 x 105 (6..9) < 4.9 10-11

MEGA M.L. Brooks 1999 1.2 4.5 1.6 17 2.5 x 108 (6..7) < 1.2 10-11

MEG ? ? ? ? 3 x 107 100 ~ 10-13


The MEGA Experiment

• Detection of in pair spectrometer• Pair production in thin lead foil

• Good resolution, but low efficiency (few %)

• Goal was 10-13, achieved was 1.2 x 10-11

• Reason for problems:• Instantaneous rate 2.5 x 108 m/s

• Design compromises

• 10-20 MHz rate/wire

• Electronics noise & crosstalk

• Lessons learned:• Minimize inst. rate

• Avoid pair spectrometer

• Carefully design electronics

• Invite MEGA people!


Photon Detectors (@ 50 MeV)

• Alternatives to Pair Spectrometer:

• Anorganic crystals:– Good efficiency, good energy resolution,

poor position resolution, poor homogeneity– NaI (much light), CsI (Ti,pure) (faster)

• Liquid Noble Gases:– No crystal boundaries– Good efficiency, resolutions

25 cm CsI

induced shower

Density 3 g/cm3

Melting/boiling point 161 K / 165 k

Radiation length 2.77 cm

Decay time 45 ns

Absorption length > 100 cm

Refractive index 1.57

Light yield 75% of NaI (Tl)

Liquid Xenon:CsI CsI

PMTPMTPMT


Liquid Xenon Calorimeter

• Calorimeter: Measure Energy, Positionand Time through scintillation light only

• Liquid Xenon has high Z and homogeneity

• ~900 l (3t) Xenon with 848 PMTs(quartz window, immersed)

• Cryogenics required: -120°C … -108°

• Extremely high purity necessary:1 ppm H20 absorbs 90% of light

• Currently largest LXe detector in theworld: Lots of pioneering work necessary

Liq. Xe

H.V.

Vacuum

for thermal insulation

Al Honeycombwindow

PMT

Refrigerator

Cooling pipe

Signals

fillerPlastic

1.5m


• Light is distributed over many PMTs

• Weighted mean of PMTs on front face x

• Broadness of distribution Dz

• Position corrected timing Dt

• Energy resolution depends on light attenuation in LXe

LXe response

3 cm

Liq. Xe

Liq. Xe

14 cm

(a)

(b)

05 10 15

2025

3035

0

10

20

30

40

50

0

2000

4000

6000

8000

10000

05

1015 20 25

3035

0

10

20

30

40

50

0

200

400

600

800

1000

1200

1400

1600

1800

52.8 MeV

52.8 MeV

x

z


• Light is distributed over many PMTs

• Weighted mean of PMTs on front face x

• Broadness of distribution z

• Position corrected timing t

• Energy resolution depends on light attenuation in LXe

LXe response

3 cm

Liq. Xe

Liq. Xe

14 cm

(a)

(b)

05 10 15

2025

3035

0

10

20

30

40

50

0

2000

4000

6000

8000

10000

05

1015 20 25

3035

0

10

20

30

40

50

0

200

400

600

800

1000

1200

1400

1600

1800

52.8 MeV

52.8 MeV

x

z


• Use GEANT to carefully study detector

• Optimize placement of PMTs according to MC results


LXe Calorimeter Prototype

¼ of the final calorimeter was build to study performance, purity, etc.

240 PMTs240 PMTs


How to get 50 MeV ’s?

• - p 0 n (Panofsky) 0

• LH2 target• Tag one with NaI & LYSO

• - p 0 n (Panofsky) 0

• LH2 target• Tag one with NaI & LYSO


Resolutions

• NaI tag: 65 MeV < E(NaI) < 95 MeV

• Energy resolution at 55 MeV:(4.8 ± 0.4) % FWHM

• LYSO tag for timing calib.:260 150 (LYSO) 140 (beam)= 150 ps (FWHM)

• Position resolution:9 mm (FWHM)

FWHM = 4.8%FWHM = 4.8%

FWHM = 260 ps

FWHM = 260 psTo be improved with refined

analysis methods

To be improved with refinedanalysis methods


Lessons learned with Prototype

• Two beam tests, many -source and cosmic runs in Tsukuba, Japan

• Light attenuation much too high (~10x)

• Cause: ~3 ppm of Water in LXe

• Cleaning with “hot” Xe-gas before filling did not help

• Water from surfaces is only absorbed in LXe

• Constant purification necessary

• Gas filter system (“getter filter”) works, attenuation length can be improved, but very slowly ( ~350 hours)

• Liquid purification is much faster

First studies in 1998, final detector ready in 2007First studies in 1998, final detector ready in 2007


Xenon storage

~900L in liquid, largest amount of LXe ever liquefied in the world

LXe CalorimeterLiquid circulating purifier

Liquid pump (100L/h)

Purifier1000L storage dewar

Cryocooler (100W)

LN2

LN2

Getter+Oxysorb

GXe pump (10-50L/min)

GXe storage tank

Cryocooler (>150W)

Heat exchanger


Final Calorimeter

Currently being assembled, will go into operation summer ‘07


Positron Spectrometer

Ultra-thin (~3g/cm2) superconducting solenoid with 1.2 T magnetic field

Homogeneous Field

e+ from +e+e+ from +e+

Gradient Field(COnstant-Bending-RAdius)

high pt track constant |p| tracks


Drift Chamber

• Measures position, time and curvature of positron tracks

• Cathode foil has three segments in a vernier pattern Signal ratio on vernier strips to determine coordinate along wire


Positron Detection System

• 16 radial DCs with extremely low mass

• He:C2H6 gas mixture

• Test beam measurementsand MC simulation:

• p/p = 0.8%

• = 10 mrad

• xvertex = 2.3 mm

FWH

M


Timing Counter

• Staves along beam axis for timing measurement

• Resolution 91 ps FWHM measured at Frascati e- - beam

• Curved fibers with APD readout for z-position

• Staves along beam axis for timing measurement

• Resolution 91 ps FWHM measured at Frascati e- - beam

• Curved fibers with APD readout for z-position

Timing resolution of BC 404

70

75

80

85

90

95

100

105

-40 -30 -20 -10 0 10 20 30 40

distance from center (cm)

90 deg

65 deg

53 deg

40 deg

Goal

Experiment Size [cm] Scintillator

PMT att [cm] FWHM[ps]

G.D. Agostini 3 x 15 x 100 NE114 XP2020 200 280

T. Tanimori 3 x 20 x 150 SCSN38 R1332 180 330

T. Sugitate 4 x 3.5 x 100 SCSN23 R1828 200 120

R.T. Gile 5 x 10 x 280 BC408 XP2020 270 260

TOPAZ 4.2 x 13 x 400

BC412 R1828 300 490

R. Stroynowski

2 x 3 x 300 SCSN38 XP2020 180 420

BELLE 4 x 6 x 255 BC408 R6680 250 210

MEG 4 x 4 x 90 BC404 R5924 270 90


The complete MEG detector

1m

e+

Liq. Xe Scin tilla tionDetector

Drift Cham ber

Liq. Xe Scin tilla tionDetector

e+

Tim ing Counter

Stopping TargetThin S uperconducting Coil

M uon Beam

Drift Cham ber


MC Simulation of full detector

e+

TC hit

“Soft” s


Beam induced background

108 /s produce 108 e+/s produce 108 /s

Cable ductsfor Drift Chamber


Detector Performance

•Prototypes of all detectors have been built and tested

• Large Prototype Liquid Xenon Detector (1/4)

• 4 (!) Drift Chambers

• Single Timing Counter Bar

•Performance has been carefully optimized

• Light yield in Xenon has been improved 10x

• Timing counter 1 ns 100 ps

• Noise in Drift Chamber reduced 10x

•Detail Monte Carlo studies were used to optimize material

•Continuous monitoring necessary to ensure stability!


Sensitivity and Background Rate

Aimed experiment parameters:

N 3 107 /s

T 2 107 s (~50 weeks)

/4 0.09

e 0.90

0.60

sel 0.70

FWHM

Ee 0.8%

E 5%

e 18 mrad

te 180 ps

Single event sensitivity (N • T • /4 • e • • sel )-1 = 3.6 10-14

Prompt Background Bpr 10-17

Accidental Background Bacc Ee • te • (E)2 • (e)2 4 10-14

90% C.L. Sensitivity 1.3 10-13

Aimed resolutions:


Current resolution estimates

Exp./Lab

Author Year Ee/Ee

%FWHM

E/E

%FWHM

te

(ns)

e

(mrad)


Duty cycle (%)

Result

SIN (PSI)

A. Van der Schaaf

1977 8.7 9.3 1.4 - (4..6) x 105 100 < 1.0 10-9

TRIUMFP.

Depommier1977 10 8.7 6.7 - 2 x 105 100 < 3.6 10-9

LANLW.W.

Kinnison1979 8.8 8 1.9 37 2.4 x 105 6.4 < 1.7 10-10

Crystal Box

R.D. Bolton 1986 8 8 1.3 87 4 x 105 (6..9) < 4.9 10-11

MEGA M.L. Brooks 1999 1.2 4.5 1.6 17 2.5 x 108 (6..7) < 1.2 10-11

MEG 2008 0.8 4.3 0.18 18 3 x 107 100 ~ 10-13


Current sensitivity estimation

• Resolutions have beenupdated constantly to seewhere we stand

• Two international reviewsper year

• People are convinced thatthe final experiment canreach 10-13 sensitivity

http://meg.web.psi.ch/docs/calculator/


How to address pile-up

• Pile-up can severely degrade the experiment performance!

• Traditional electronics cannot detect pile-up

TDC

Amplifier Discriminator Measure Time

Need fullwaveform digitization

to reject pile-up

Need fullwaveform digitization

to reject pile-up


• Need 500 MHz 12 bit digitization for Drift Chamber system

• Need 2 GHz 12 bit digitization for Xenon Calorimeter + Timing Counters

• Need 3000 Channels

• At affordable price

Waveform Digitizing

Solution: Develop own“Switched Capacitor Array” Chip

Solution: Develop own“Switched Capacitor Array” Chip


The Domino Principle

Shift RegisterClock

IN

Out

“Time stretcher” GHz MHz“Time stretcher” GHz MHz

Waveform stored

Inverter “Domino” ring chain0.2-2 ns

FADC 33 MHz

Keep Domino wave running in a circular fashion and stop by trigger Domino Ring Sampler (DRS)

Keep Domino wave running in a circular fashion and stop by trigger Domino Ring Sampler (DRS)


The DRS chip3

2 c

han

nels

in

pu

t

• DRS chip developed at PSI

• 5 GHz sampling speed, 12 bits resolution

• 12 channels @ 1024 bins on one chip

• Typical costs ~60 € / channel

• 3000 Channels installed in MEG

• Licensing to Industry (CAEN) in progress

• DRS chip developed at PSI

• 5 GHz sampling speed, 12 bits resolution

• 12 channels @ 1024 bins on one chip

• Typical costs ~60 € / channel

• 3000 Channels installed in MEG

• Licensing to Industry (CAEN) in progress


Waveform examples

“virtual oscilloscope”“virtual oscilloscope” pulse shape discriminationpulse shape discrimination

original:

firstderivation:

t = 15ns

Crosstalk removal by subtracting empty channelCrosstalk removal by subtracting empty channel

Quantum Step in Technology!

Quantum Step in Technology!


DAQ System Principle

Active Splitter

Drift Chamber Liquid Xenon Calorimeter Timing Counter

WaveformDigitizing

Trigger

TriggerEvent number

Event type

Busy

Rack PC

Rack PC

Rack PC

Rack PC

Rack PC

opticallink

(SIS3100)

Rack PC

Rack PC

Rack PC

Rack PC

Event Builder

Switch

GBit Ethernet

LVDS parallel bus

VME VME


DAQ System

• Use waveform digitization (500 MHz/2 GHz) on all channels

• Waveform pre-analysis directly in online cluster (zero suppression, calibration) using multi-threading

• MIDAS DAQ Software

• Data reduction: 900 MB/s 5 MB/s

• Data amount: 100 TB/year

• Use waveform digitization (500 MHz/2 GHz) on all channels

• Waveform pre-analysis directly in online cluster (zero suppression, calibration) using multi-threading

• MIDAS DAQ Software

• Data reduction: 900 MB/s 5 MB/s

• Data amount: 100 TB/year

2000 channelswaveform digitizing

DAQ cluster

Monitoring

How to keep the experiment stable?


Long time stability

• Especially the calorimeter needs to run stably over years

• Primary problem: Gain drift of PMT might shift background event into signal region

• If we find e , are we sure it’s not an artifact?

• Need sophisticated continuous calibration!

• Unfortunately, there is no 52.8 MeV source available

E[MeV]

N 52.8 MeV

e

e


Planned Calorimeter Calibrations

Combine calibration methods different in complexity and energy:

Method Energy Frequency

LED pulser ~few MeV Continuously241Am source on wire

5.6 MeV Continuously

n capture on Ni 9 MeV daily

p+ 7Li 17.6 MeV daily

0 production on LH2

54 – 82 MeV

monthly ?

LED100 m gold-plated tungsten wire

n 58Ni9 MeV


7Li(p,)8Be Spectrum

7Li (p,)8Be resonant at Ep= 440 keV =14 keV peak = 5 mbE0 = 17.6 MeVE1 = 14.6 MeV 6.1 MeVBpeak 0/(0+ 1)= 0.72

7Li (p,)8Be resonant at Ep= 440 keV =14 keV peak = 5 mbE0 = 17.6 MeVE1 = 14.6 MeV 6.1 MeVBpeak 0/(0+ 1)= 0.72

NaI 12”x12” spectrumNaI 12”x12” spectrum

1

Crystal Ball DataCrystal Ball Data

0


CW Accelerator

• 1 MeV protons• 100 A• HV

Engineering, Amersfoort, NL

• 1 MeV protons• 100 A• HV

Engineering, Amersfoort, NL

beam spot

+ -

p+


0 Calibration

NaI

target

00

• Tune beam line to -

• Use liquid H2 target

• -p n

• Tag one with movable NaI counter

• Beamline & target change take ~1 day

• Tune beam line to -

• Use liquid H2 target

• -p n

• Tag one with movable NaI counter

• Beamline & target change take ~1 day


Midas Slow Control Bus System

BTS Magnet LXe purifier LXe storage LXe cryostat NaI mover

COBRADC gas system A/C hut Cooling water VME Crates HV

Beamline

PC• All subsystems controlled by same MSCB system• All data on tape• Central alarm and history system• Also used now at: SR, SLS, nEDM, TRIUMF

• All subsystems controlled by same MSCB system• All data on tape• Central alarm and history system• Also used now at: SR, SLS, nEDM, TRIUMF

MSCB

HVR SCS-2000

Status and Outlook

Where are we, where do we go?


Current Status

• Goal: Produce “significant” result before LHC

• R & D phase took longer than anticipated

• We are currently in the set-up and engineering phase, detector is expectedto be completed end of 2007

• Data taking will go 2008-2010

R&D

199920002001200220032004200520062007200820092010

Engineering

DataTaking

Set-up

http://meg.psi.chhttp://meg.psi.ch


What next?

Will we find e ?

No

• Improve experiment from 10-13 to 10-14:

• Denser PMTs

• Second Calorimeter

• Improve experiment from 10-13 to 10-14:

• Denser PMTs

• Second Calorimeter

Yes

• Carefully check results

• Be happy

• Most extensions of the SM (SUSY, Little Higgs, Extra Dimensions)predict e

More experiments needed

• Carefully check results

• Be happy

• Most extensions of the SM (SUSY, Little Higgs, Extra Dimensions)predict e

More experiments needed


“Polarized” MEG

• are produced already polarized

• Different target to keep polarization

• Angular distribution of decays predicteddifferently by different theories(compare Wu experiment for Parity Violation)

SU(5) SUSY-GUT A = +1SO(10) SUSY-GUT A 0MSSM with R A = -1

SU(5) SUSY-GUT A = +1SO(10) SUSY-GUT A 0MSSM with R A = -1

Detector acceptance

Y.Kuno et al.,Phys.Rev.Lett. 77 (1996) 434

2

cos1)(

cos

)( e

e

APeBR

d

edN


Expected Distribution

• A = +1• B (+ e+ ) = 1 x 10-12

• 1 x 108 +/s• 5 x 107 s beam time (2 years)• P = 0.97

• A = +1• B (+ e+ ) = 1 x 10-12

• 1 x 108 +/s• 5 x 107 s beam time (2 years)• P = 0.97

S. Yamada @ SUSY 2004, Tsukuba

Signal +Background

Background


Conclusions

• The MEG Experiment has good prospectives to improve the current limit for e by two orders of magnitude

• Pushing the detector technologies takes time

• The experiment is now starting up, so expect exciting results in 2008/2009

http://meg.psi.ch

Lepton Flavor Violation: Goals and Status of the MEG Experiment at PSI Stefan Ritt Paul Scherrer...

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Transcript of Lepton Flavor Violation: Goals and Status of the MEG Experiment at PSI Stefan Ritt Paul Scherrer...