Lepton Flavor Violation Goals and Status of the

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

Agenda Search for m e down to 10 -13 • Motivation • Experimental Method • Status and Outlook 26 June '07 Particle Colloquium Heidelberg 2

Motivation Why should we search for m e g ?

The Standard Model Fermions (Matter) u Leptons 26 June '07 t g up charm top photon d s b g down strange bottom ne nm nt electron neutrino muon neutrino tau neutrino e m t electron I muon II gluon W W boson Z Z boson tau III Particle Colloquium Heidelberg Force carriers Quarks Generation c Bosons Higgs* boson *) Yet to be confirmed 4

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 Today’s goal is to look for physics beyond the standard model 26 June '07 Particle Colloquium Heidelberg CDF 5

Beyond the SM Find New Physics Beyond the SM High Energy Frontier High Precision Frontier • Produce heavy new particles directly • Heavy particles need large colliders • Complex detectors • Look for small deviations from SM (g-2)m , CKM unitarity • Look forbidden decays • Requires high precision at low energy 26 June '07 Particle Colloquium Heidelberg 6

Neutron beta decay Neutron b decay via intermediate heavy W- boson ~80 Me. V ne W- e- Neutron mean life time: 886 s ~5 Me. V n u d d u p n p+ + e - + ne 26 June '07 Particle Colloquium Heidelberg b decay discovery: ~1934 W- discovery: 1983 7

New physics in m decay Can’t we do the same in m decay? m- ? e- Probe physics at Te. V scale with high precision m decay measurement 26 June '07 Particle Colloquium Heidelberg 8

The Muon Seth Neddermeyer • Discovery: 1936 in cosmic radiation ne • Mass: 105 Me. V/c 2 • Mean lifetime: 2. 2 ms W- e. Carl Anderson ≈ 100% m- nm 0. 014 < 10 -11 led to Lepton Flavor Conservation as “accidental” symmetry 26 June '07 Particle Colloquium Heidelberg 9

Lepton Flavor Conservation • Absence of processes such as m 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 26 June '07 Particle Colloquium Heidelberg 10

LFV and Neutrino Oscillations Neutrino mass m e g possible even in the SM W- m- nm ne e- LFV in the charged sector is forbidden in the Standard Model n mixing 26 June '07 Particle Colloquium Heidelberg 11

LFV in SUSY • While LFV is forbidden in SM, it is possible in SUSY W- m- nm e- ne ≈ 10 -12 m- e- Current experimental limit: BR(m e ) < 10 -11 26 June '07 Particle Colloquium Heidelberg 12

LFV Summary • 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 m 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 m/s DC beam needed • ~ 2 years measurement time • excellent background suppression 26 June '07 Particle Colloquium Heidelberg 13

History of LFV searches cosmic m • Long history dating back to 1947! 10 -1 • Best present limits: • 1. 2 x 10 -11 (MEGA) 10 -3 • m. Ti → e. Ti < 7 x 10 -4 • m → eee < 1 x 10 -13 m→eg m. A → e. A m → eee 10 -2 (SINDRUM II) 10 -12 (SINDRUM II) • MEG Experiment aims at 10 -13 10 -5 stopped p 10 -6 10 -7 m beams 10 -6 • Improvements linked to advance in technology stopped m 10 -9 10 -10 10 -11 SUSY SU(5) BR(m e g) = 10 -13 m. Ti e. Ti = 4 x 10 -16 BR(m eee) = 6 x 10 -16 26 June '07 10 -12 10 -13 MEG 10 -14 10 -15 1940 1950 1960 Particle Colloquium Heidelberg 1970 1980 1990 2000 2010 14

Current SUSY predictions ft(M)=2. 4 m>0 Ml=50 Ge. V 1) current limit MEG goal tan b “Supersymmetric parameterspace accessible by LHC” 1) 2) J. Hisano et al. , Phys. Lett. B 391 (1997) 341 MEGA collaboration, hep-ex/9905013 26 June '07 W. Buchmueller, DESY, priv. comm. Particle Colloquium Heidelberg 15

LFV link to other SUSY proc. me-LFV m(g-2)m e- mm. EDM slepton mixing matrix: m- In SO(10), e. EDM is related to m e : R. Barbieri et al. , hep-ph/9501334 m 26 June '07 m. Particle Colloquium Heidelberg 16

Experimental Method How to detect m e g ?

Decay topology m e g m eg 52. 8 Me. V N m 52. 8 Me. V 180º 10 e 20 30 40 50 60 E [Me. V] N 52. 8 Me. V m • • • → e signal very clean Eg = Ee = 52. 8 Me. V q e = 180º e and in time 52. 8 Me. V 10 26 June '07 20 Particle Colloquium Heidelberg 30 40 50 60 Ee[Me. V] 18

Michel Decay (~100%) N Three body decay: wide energy spectrum 52. 8 Me. V Theoretical n m e nn m n Ee[Me. V] e N 52. 8 Me. V Convoluted with detector resolution Ee[Me. V] 26 June '07 Particle Colloquium Heidelberg 19

Radiative Muon Decay (1. 4%) N n 52. 8 Me. V m e nn m n e E [Me. V] “Prompt” Background 26 June '07 Particle Colloquium Heidelberg 20

“Accidental” Background m eg Background n m e nn m m n e Annihilation in flight 180º e e n m m e nn n m • • • → e signal very clean Eg = Ee = 52. 8 Me. V q e = 180º e and in time 26 June '07 Good energy resolution Good spatial resolution Excellent timing resolution Good pile-up rejection Particle Colloquium Heidelberg 21

Previous Experiments DEe/Ee %FWH M DE /E %FWH M Dte (ns ) Dqe (mra d) Inst. Stop rate (s-1) Duty cycle (%) 197 7 8. 7 9. 3 1. 4 - (4. . 6) x 105 100 < 1. 0 10 - 197 7 10 8. 7 6. 7 - 2 x 105 100 < 3. 6 10 - Exp. / Lab Author Yea r SIN (PSI) A. Van der Schaaf P. TRIUM Depommie F r Result 9 9 LANL W. W. Kinnison 197 9 8. 8 8 1. 9 37 2. 4 x 105 6. 4 < 1. 7 10 - Crystal Box R. D. Bolton 198 6 8 8 1. 3 87 4 x 105 (6. . 9) < 4. 9 10 - MEGA M. L. Brooks 199 9 1. 2 4. 5 1. 6 17 2. 5 x 108 (6. . 7) < 1. 2 10 - ? ? ? ~ 10 -13 MEG 10 11 11 How can we achieve a quantum step in detector technology? 26 June '07 Particle Colloquium Heidelberg 22

How to build a good experiment? 26 June '07 Particle Colloquium Heidelberg 23

Collaboration ~70 People (40 FTEs) from five countries 26 June '07 Particle Colloquium Heidelberg 24

Paul Scherrer Institute Proton Accelerator Swiss Light Source 26 June '07 Particle Colloquium Heidelberg 25

PSI Proton Accelerator 26 June '07 Particle Colloquium Heidelberg 26

Generating muons Carbon Target p+ m+ Me. V/c 2 590 Protons 1. 8 m. A = 1016 p+/s 108 m+/s m+ p+ 26 June '07 Particle Colloquium Heidelberg 27

Muon Beam Structure Muon beam structure differs for different accelerators Pulsed muon beam, LANL DC muon beam, PSI Instantaneous rate much higher in pulsed beam Duty cycle: Ratio of pulse width over period Duty cycle: 6 % Duty cycle: 100 % 26 June '07 Particle Colloquium Heidelberg 28

Muon Beam Line Transport 108 m+/s to stopping target inside detector with minimal background - Lorentz Force vanishes for given v: x x x m+ e+ + Wien Filter m+ from production target 26 June '07 Particle Colloquium Heidelberg 29

Results of beam line optimization Rm ~ 1. 1 x 108 m+/s at experiment e+ m+ s ~ 10. 9 mm m+ 26 June '07 Particle Colloquium Heidelberg 30

Previous Experiments DEe/Ee %FWH M DE /E %FWH M Dte (ns ) Dqe (mra d) Inst. Stop rate (s-1) Duty cycle (%) 197 7 8. 7 9. 3 1. 4 - (4. . 6) x 105 100 < 1. 0 10 - 197 7 10 8. 7 6. 7 - 2 x 105 100 < 3. 6 10 - Exp. / Lab Author Yea r SIN (PSI) A. Van der Schaaf P. TRIUM Depommie F r Result 9 9 LANL W. W. Kinnison 197 9 8. 8 8 1. 9 37 2. 4 x 105 6. 4 < 1. 7 10 - Crystal Box R. D. Bolton 198 6 8 8 1. 3 87 4 x 105 (6. . 9) < 4. 9 10 - MEGA M. L. Brooks 199 9 1. 2 4. 5 1. 6 17 2. 5 x 108 (6. . 7) < 1. 2 10 - ? ? 3 x 107 100 ~ 10 -13 MEG 26 June '07 Particle Colloquium Heidelberg 10 11 11 31

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! 26 June '07 Particle Colloquium Heidelberg 32

Photon Detectors (@ 50 Me. V) • Alternatives to Pair Spectrometer: induced shower • Anorganic crystals: – Good efficiency, good energy resolution, poor position resolution, poor homogeneity – Na. I (much light), Cs. I (Ti, pure) (faster) • Liquid Noble Gases: – No crystal boundaries – Good efficiency, resolutions Liquid Xenon: 26 June '07 25 cm Cs. I Density 3 g/cm 3 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 Na. I Particle Colloquium (Tl) Heidelberg Cs. I PMT PMT 33

Liquid Xenon Calorimeter • Calorimeter: Measure Energy, Position and Time through scintillation light only • Liquid Xenon has high Z and homogeneity Refrigerator • Extremely high purity necessary: 1 ppm H 20 absorbs 90% of light • Currently largest LXe detector in the world: Lots of pioneering work necessary 26 June '07 Particle Colloquium Heidelberg Signals Cooling pipe • ~900 l (3 t) Xenon with 848 PMTs (quartz window, immersed) • Cryogenics required: -120°C … -108° H. V. Vacuum Liq. Xe for thermal insulation Al Honeycomb window m PMT Plasticfiller 1. 5 m 34

LXe response • 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 26 June '07 x z Particle Colloquium Heidelberg 35

LXe response • Light is distributed over many PMTs • Weighted mean of PMTs on front face Dx • Broadness of distribution Dz • Position corrected timing Dt • Energy resolution depends on light attenuation in LXe 26 June '07 x z Particle Colloquium Heidelberg 36

• Use GEANT to carefully study detector • Optimize placement of PMTs according to MC results 26 June '07 Particle Colloquium Heidelberg 37

LXe Calorimeter Prototype ¼ of the final calorimeter was build to study performance, purity, etc. 240 PMTs 26 June '07 Particle Colloquium Heidelberg 38

How to get 50 Me. V ’s? • p- p p 0 n (Panofsky) p 0 • LH 2 target • Tag one with Na. I & LYSO 26 June '07 Particle Colloquium Heidelberg 39

Resolutions • Na. I tag: 65 Me. V < E(Na. I) < 95 Me. V • Energy resolution at 55 Me. V: (4. 8 ± 0. 4) % FWHM • LYSO tag for timing calib. : 260 150 (LYSO) 140 (beam) = 150 ps (FWHM) FWHM = 4. 8% • Position resolution: 9 mm (FWHM) To be improved with refined analysis methods 26 June '07 Particle Colloquium Heidelberg FWHM = 260 ps 40

Lessons learned with Prototype • Two beam tests, many a-source and cosmic runs in Tsukuba, Japan • Light attenuation much too high (~10 x) • 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 (t ~350 hours) • Liquid purification is much faster First studies in 1998, final detector ready in 2007 26 June '07 Particle Colloquium Heidelberg 41

Xenon storage ~900 L in liquid, largest amount of LXe ever liquefied in the world GXe pump (10 -50 L/min) Heat exchanger GXe storage tank Getter+Oxysorb Cryocooler (100 W) LN 2 Cryocooler (>150 W) Liquid pump (100 L/h) Purifier LXe Calorimeter 26 June '07 Liquid circulating purifier 1000 L storage dewar Particle Colloquium Heidelberg 42

Final Calorimeter Currently being assembled, will go into operation summer ‘ 07 26 June '07 Particle Colloquium Heidelberg 43

Positron Spectrometer Ultra-thin (~3 g/cm 2) superconducting solenoid with 1. 2 T magnetic field Homogeneous Field high pt track constant |p| tracks Gradient Field (COnstant-Bending-RAdius) 26 June '07 Particle Colloquium Heidelberg e+ from m+ e+ 44

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 26 June '07 Particle Colloquium Heidelberg 45

Positron Detection System • 16 radial DCs with extremely low mass • He: C 2 H 6 gas mixture • Test beam measurements and MC simulation: • Dq = 10 mrad • Dxvertex = 2. 3 mm 26 June '07 FWHM • Dp/p = 0. 8% Particle Colloquium Heidelberg 46

Timing Counter Experiment Size [cm] Scintillator PMT latt [cm] FWHM[ps] G. D. Agostini 3 x 15 x 100 NE 114 XP 2020 200 280 T. Tanimori 3 x 20 x 150 SCSN 38 R 1332 180 330 T. Sugitate 4 x 3. 5 x 100 SCSN 23 R 1828 200 120 R. T. Gile 5 x 10 x 280 BC 408 XP 2020 270 260 TOPAZ 4. 2 x 13 x 400 BC 412 R 1828 300 490 R. Stroynowski 2 x 300 SCSN 38 XP 2020 180 420 BELLE 4 x 6 x 255 BC 408 R 6680 250 210 MEG 4 x 90 BC 404 R 5924 270 90 26 June '07 Particle Colloquium Heidelberg • Staves along beam axis for timing measurement • Resolution 91 ps FWHM measured at Frascati e- - beam • Curved fibers with APD readout for z-position 47

The complete MEG detector 26 June '07 Particle Colloquium Heidelberg 48

MC Simulation of full detector e+ “Soft” s TC hit 26 June '07 Particle Colloquium Heidelberg 49

Beam induced background 108 m/s produce 108 e+/s produce 108 /s Cable ducts for Drift Chamber 26 June '07 Particle Colloquium Heidelberg 50

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 10 x • Timing counter 1 ns 100 ps • Noise in Drift Chamber reduced 10 x • Detail Monte Carlo studies were used to optimize material • Continuous monitoring necessary to ensure stability! 26 June '07 Particle Colloquium Heidelberg 51

Sensitivity and Background Rate Aimed experiment parameters: Aimed resolutions: Nm 3 107 /s T 2 107 s (~50 weeks) W/4 p 0. 09 DEe 0. 8% ee 0. 90 DE 5% e 0. 60 Dqe 18 mrad esel 0. 70 Dte 180 ps FWHM Single event sensitivity (Nm • T • W/4 p • ee • esel )-1 = 3. 6 10 -14 Prompt Background Bpr 10 -17 Accidental Background Bacc DEe • Dte • (DE )2 • (Dqe )2 4 10 -14 90% C. L. Sensitivity 1. 3 10 -13 26 June '07 Particle Colloquium Heidelberg 52

Current resolution estimates Exp. / Lab Author Yea DEe/Ee r %FW HM DE /E %FWH M Dte (ns) Dqe (mra d) Inst. Stop rate (s-1) Duty cycl e (%) Result SIN (PSI) A. Van der Schaaf 197 7 8. 7 9. 3 1. 4 - (4. . 6) x 105 100 < 1. 0 10 -9 TRIUM F P. Depommi er 197 7 10 8. 7 6. 7 - 2 x 105 100 < 3. 6 10 -9 LANL W. W. Kinnison 197 9 8. 8 8 1. 9 37 2. 4 x 105 6. 4 < 1. 7 10 - Crystal Box R. D. Bolton 198 6 8 8 1. 3 87 4 x 105 (6. . 9) < 4. 9 10 - MEGA M. L. Brooks 199 9 1. 2 4. 5 1. 6 17 2. 5 x 108 (6. . 7) < 1. 2 10 - 200 8 0. 8 4. 3 0. 18 18 MEG 26 June '07 Particle Colloquium Heidelberg 3 x 107 100 10 11 11 ~ 10 -13 53

Current sensitivity estimation • Resolutions have been updated constantly to see where we stand • Two international reviews per year • People are convinced that the final experiment can reach 10 -13 sensitivity http: //meg. web. psi. ch/docs/calculator/ 26 June '07 Particle Colloquium Heidelberg 54

How to address pile-up • Pile-up can severely degrade the experiment performance! • Traditional electronics cannot detect pile-up TDC Amplifier 26 June '07 Discriminator Need full waveform digitization to reject pile-up Measure Time Particle Colloquium Heidelberg 55

Waveform Digitizing • 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 Solution: Develop own “Switched Capacitor Array” Chip 26 June '07 Particle Colloquium Heidelberg 56

The Domino Principle 0. 2 -2 ns Inverter “Domino” ring chain IN Waveform stored Clock Shift Register Out FADC 33 MHz “Time stretcher” GHz MHz Keep Domino wave running in a circular fashion and stop by trigger Domino Ring Sampler (DRS) 26 June '07 Particle Colloquium Heidelberg 57

The DRS chip • DRS chip developed at PSI • 5 GHz sampling speed, 12 bits resolution • 12 channels @ 1024 bins on one chip 32 channels input • Typical costs ~60 € / channel 26 June '07 • 3000 Channels installed in MEG • Licensing to Industry (CAEN) in progress Particle Colloquium Heidelberg 58

Waveform examples “virtual oscilloscope” original: Q m u t n ua first derivation: 26 June '07 pulse shape discrimination p e St ! y g o l o n h c e T in Crosstalk removal by subtracting empty channel Dt = 15 ns Particle Colloquium Heidelberg 59

DAQ System Principle Liquid Xenon Calorimeter Drift Chamber Timing Counter Active Splitter LV DS VME pa ra lle lb Trigger Event number Event type us optical link (SIS 3100) Waveform Digitizing Rack PC Trigger Busy GBi t Et Rack PC hern et Switch Rack PC Rack PC Event Builder 26 June '07 Particle Colloquium Heidelberg 60

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 2000 channels waveform digitizing 26 June '07 DAQ cluster Particle Colloquium Heidelberg 61

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 m e g , are we sure it’s not an artifact? • Need sophisticated continuous calibration! • Unfortunately, there is no 52. 8 Me. V source available N 52. 8 Me. V m e m e nn E [Me. V] 26 June '07 Particle Colloquium Heidelberg 63

Planned Calorimeter Calibrations Combine calibration methods different in complexity and energy: Method Energy Frequency LED pulser ~few Me. V Continuously 241 Am 5. 6 Me. V a Continuously n capture on Ni 9 Me. V daily p+ 7 Li 17. 6 Me. V daily p 0 production on LH 2 54 – 82 Me. V monthly ? source on wire 100 mm gold-plated tungsten wire 26 June '07 n 58 Ni 9 Me. V LED Particle Colloquium Heidelberg 64

7 Li(p, )8 Be Spectrum 7 Li (p, )8 Be resonant at Ep= 440 ke. V =14 ke. V peak = 5 mb E 0 = 17. 6 Me. V E 1 = 14. 6 Me. V 6. 1 Me. V Bpeak 0/( 0+ 1)= 0. 72 Crystal Ball Data 1 Na. I 12”x 12” 26 June '07 0 spectrum Particle Colloquium Heidelberg 65

CW Accelerator • 1 Me. V protons • 100 m. A • HV Engineering, Amersfoort, NL beam spot p+ m+ p - 26 June '07 Particle Colloquium Heidelberg 66

p 0 Calibration • Tune beam line to p • Use liquid H 2 target • p- p p 0 n Na. I p 0 q • Tag one with movable Na. I counter • Beamline & target change take ~1 day target 26 June '07 Particle Colloquium Heidelberg 67

Midas Slow Control Bus System BTS Magnet Beamline LXe purifier LXe storage LXe cryostat Na. I mover MSCB DC gas system • • A/C hut VME Crates HV All subsystems controlled by same MSCB system All data on tape Central alarm and history system Also used now at: m. SR, SLS, n. EDM, TRIUMF HVR 26 June '07 Cooling water COBRA PC SCS-2000 Particle Colloquium Heidelberg 68

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 http: //meg. psi. ch • We are currently in the set-up and engineering phase, detector is expected to be completed end of 2007 • Data taking will go 2008 -2010 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 26 June '07 R&D Set-up Engineering Data Taking Particle Colloquium Heidelberg 70

What next? Will we find m e ? Yes No • Improve experiment from 10 -13 to 10 -14: • Denser PMTs • Second Calorimeter • Carefully check results • Be happy • Most extensions of the SM (SUSY, Little Higgs, Extra Dimensions) predict m e More experiments needed 26 June '07 Particle Colloquium Heidelberg 71

“Polarized” MEG • m are produced already polarized • Different target to keep m polarization • Angular distribution of decays predicted differently by different theories (compare Wu experiment for Parity Violation) Detector acceptance SU(5) SUSY-GUT A = +1 SO(10) SUSY-GUT A 0 MSSM with n. R A = -1 Y. Kuno et al. , Phys. Rev. Lett. 77 (1996) 434 26 June '07 Particle Colloquium Heidelberg 72

Expected Distribution • • • A = +1 B (m+ e+ ) = 1 x 10 -12 1 x 108 m+/s 5 x 107 s beam time (2 years) Pm = 0. 97 Signal + Background S. Yamada @ SUSY 2004, Tsukuba 26 June '07 Background Particle Colloquium Heidelberg 73

Conclusions • The MEG Experiment has good prospectives to improve the current limit for m e g 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 26 June '07 Particle Colloquium Heidelberg 74