1. 12 Sepetmber 2008 Paolo Walter Cattaneo 1 Perspectives beyond MEG Paolo Walter Cattaneo INFN Pavia Neutrino Oscillation Workshop Conca Specchiulla, Otranto, Lecce (ITALY) 6 – 13 September 2008

2. 12 Sepetmber 2008 Paolo Walter Cattaneo 2 Outline Theoretical motivations for searching for LFV.Theoretical motivations for searching for LFV. The muonic channel:The muonic channel:    e  (MEG);    e conversion (MECO, PRIME);     conversion (a brief mention);  Future perspectives. The tauonic channel:The tauonic channel:    , e  (BABAR, BELLE);    lll (BABAR, BELLE);  Other decays (   lh,   lhh …) (BABAR, BELLE);  Future perspectives. Conclusions.Conclusions.

3. 12 Sepetmber 2008 Paolo Walter Cattaneo 3 Theoretical motivations In the Standard Model with massive Dirac neutrinos LFV processes (as   ,   ,   eee,  A  eA..) are predicted at unmeasurably small levels (BR ~ 10 -50 ). In the Standard Model with massive Dirac neutrinos LFV processes (as   e ,   ,   eee,  A  eA..) are predicted at unmeasurably small levels (BR ~ 10 -50 ). However, Most of the beyond SM models predict such processes at much larger rates. Since the SM background is negligible, LFV processes are clear evidences for Physisca beyond SM.

4. 12 Sepetmber 2008 Paolo Walter Cattaneo 4 The muonic channel

5. 12 Sepetmber 2008 Paolo Walter Cattaneo 5 5 1 10 -2 10 -4 10 -16 10 -6 10 -8 10 -10 10 -14 10 -12 1940 1950 1960 1970 1980 1990 2000 2010 History of Lepton Flavor Violation with   - N  e - N  +  e +   +  e + e + e - MEGA SINDRUM2 Branching Fraction Upper Limit MEG goal -  - N→e - N goal

6. 12 Sepetmber 2008 Paolo Walter Cattaneo 6 SUSY predictions for   e  LFV induced by finite slepton mixing through radiative corrections. MEG goal J. Hisano et al., Phys. Lett. B391 (1997) 341 SUSY SU(5) model Experimental Bound (MEGA Coll., PRD 65 (2002) 112002) In SO(10) BR SO(10)  10 BR SU(5) (R. Barbieri et al., Phys. Lett. B338 (1994) 212, Nucl. Phys. B445 (1995) 215) In general beyond the SM predicts BR(  e  )  BR  eee  BR  eee   BR  eA 

7. 12 Sepetmber 2008 Paolo Walter Cattaneo 7  e  : Signal and Background e+ +  e+ + e+ +  e+ +   e  = 180° E e = E  = 52.8 MeV T e = T  signal   e  background prompt   e  e+ +  e+ + e+ +  e+ +  accidental   e    e  ee   eZ  eZ  e+ + e+ +e+ + e+ + Vanishing E energy

8. 12 Sepetmber 2008 Paolo Walter Cattaneo 8 Summary of MEG sensitivity BR (   e  )  1 10 -13 Upper Limit @ 90 % C.L. BR acc  R   E e (  E   2 (    2  t   3 10 -15 Accidental Background BR corr  1 10 -15 Correlated Background N sig = BR T R   /4   e  sel   Signal SES = 1/(T R   /4   e  sel      4 10 -14 Single Event Sensitivity 4 events (P = 2 10 -3 ) correspond to BR = 2 10 -13 Discovery  e /E e = 1.0%   /E  = 4.0%  e 0.6    0.6  sel  (0.9) 3 = 0.7  e  0.6    0.6  sel  (0.9) 3 = 0.7  /4  = 0.09 Detector parameters R  = 3.0 10 7  + /s Duty cycle 100% T = 2.5 10 7 s  t e   ps  e   mrad

9. 12 Sepetmber 2008 Paolo Walter Cattaneo 9 What next for   e  ? 1) Which gain in sensitivity can be expected using more intense muon beams (  10 10  /s) ? For a 0 background experiment with R  tunable R  opt  1/sqrt(T  /4   e  sel    E e  t    1/(  E      R  opt  1/sqrt(T  /4   e  sel    E e  t    1/(  E      SES opt  (  E      sqrt  E e  t    sqrt(T  /4   e  sel    Linear improvements are obtained only with  E  and   At PSI R  max    as far as R  max > R  opt rate is not a limitation A factor 10 to be gained to reach BR(   e  )  1 10 -14 Either a detector technology breakthrough or several small (factors 1.5-2.0) improvements

10. 12 Sepetmber 2008 Paolo Walter Cattaneo 10 Most limiting factors : performances of e.m. calorimeter MEG Lxe is state of the art technology Most limiting factors : performances of e.m. calorimeter MEG Lxe is state of the art technology Some possible improvements: Some possible improvements: - high resolution beta spectrometers (  E e /E e = 0.1 %), geometrical acceptance ?? ; - high resolution beta spectrometers (  E e /E e = 0.1 %), geometrical acceptance ?? ; - thinner target to improve   ( exploiting higher intensity muon beams ), off target decay increase pileup background?? ; - thinner target to improve   ( exploiting higher intensity muon beams ), off target decay increase pileup background?? ; - finely segmented active target (to improve e  match), concept to be developed ; - finely segmented active target (to improve e  match), concept to be developed ; Substantial RD needed !!! What next for   e  ? 2)

11. 12 Sepetmber 2008 Paolo Walter Cattaneo 11  3e status BR(  3e) ~  BR(  e  ) ~ 10 -2 BR(  e  ) 20 year old limit BR(  3e) < 10 -12 (SINDRUM Coll., Nucl. Phys. B299 (1988) 1) BR acc  10 -13  R   R  max = 5 10 6  /s Exploit  E e = M   time coincidence and coplanarity  Also limited by accidental background. ( Michel positron and an e + e - pair produced by Bhabha scattering in the target ) Experimental advantage: no photons  no e.m. calorimeter. However: very high rate in tracking system  dead time, trigger & pattern recognition problems ; need of large modularity.  large angular and momentum acceptance of spectrometer

12. 12 Sepetmber 2008 Paolo Walter Cattaneo 12  3e the future  3e the future To be competitive with MEG predicted limit BR(  e  )<10 -13 BR(  3e) <  10 -15 !! Total efficiency in SINDRUM  Cannot be improved much!! To match the BR goal R  must increase by 10 3 to R  = 5 10 9  /s Br acc increase of a factor 10 6 !! MEG timing system improve resolution of factor of 10 Recover 10 5 from tracking and material reduction appears extremely difficult. No experimet proposal in the last 20 years

13. 12 Sepetmber 2008 Paolo Walter Cattaneo 13  - A  e - A: Conversion Mechanism  - are stopped in material foils ( Al for MECO, Ti for PRIME) forming muonic atoms.  - are stopped in material foils ( Al for MECO, Ti for PRIME) forming muonic atoms. Three possible fates for the muon: Three possible fates for the muon:  Nuclear capture;  Three body decay in orbit;  Coherent LFV decay (extra factor of Z in the rates). Signal is a single monochromatic electron:  Signal is a single monochromatic electron:  E e = m m – E recoil – E binding  105.0 MeV (Al), 104.3 MeV (Ti) E e = m m – E recoil – E binding  105.0 MeV (Al), 104.3 MeV (Ti)   in Al ~ 0.9  s, in Ti ~ 0.35  s ( in vacuum: 2.2  s).   in Al ~ 0.9  s, in Ti ~ 0.35  s ( in vacuum: 2.2  s).

14. 12 Sepetmber 2008 Paolo Walter Cattaneo 14  - A  e - A: Signal and Background E e sig = m   – E B - E R signal  (A,Z)  e (A,Z) main backgrounds MIO (muon decay in orbit)  (A,Z)  e  (A,Z) E e max = m   – E B – E R dN/dE e  (E max – E e ) 5 e- -  e- - e- -  e- -  (A,Z) RMC ( radiative  capture ) (A,Z)  (A,Z-1)  e + e - Beam related background! No coincidence  no accidental background RPC ( radiative  capture ) (A,Z)  (A,Z-1)  e + E e max > E e sig !!

15. 12 Sepetmber 2008 Paolo Walter Cattaneo 15 Reduction of beam background 1) Beam pulsing: Muonic atoms have some hundreds of nslifetime use a pulsed Muonic atoms have some hundreds of nslifetime use a pulsed beam with buckets short compared to this lifetime, leave beam with buckets short compared to this lifetime, leave  decay and measure in a delayed time window.  decay and measure in a delayed time window. 2) Beam quality: - insert a moderator to reduce the  contamination (pion range  0.5 muon range); a 10 6 reduction factor obtained by SINDRUM II. No more than 10 5  may stop in the range  0.5 muon range); a 10 6 reduction factor obtained by SINDRUM II. No more than 10 5  may stop in the target during the full measurement (  1 background event); target during the full measurement (  1 background event); - select a beam momentum  70 MeV/c (  decaying in flight produce low energy electrons). flight produce low energy electrons).

16. 12 Sepetmber 2008 Paolo Walter Cattaneo 16 Present limit: SINDRUM II (PSI) SINDRUM II parameters – beam intensity3 x 10 7   /s –   momentum53 MeV/c – magnetic field0.33T – acceptance 7% – momentum res.2% FWHM – S.E.S3.3 x 10 -13 – B(  - Au  e - Au )  8 x 10 -13

17. 12 Sepetmber 2008 Paolo Walter Cattaneo 17 The MECO/MU2E Experiment Expected 10 11 stopping  /s (1000–fold increase in  beam intensity) forExpected 10 11 stopping  /s (1000–fold increase in  beam intensity) for a proton current of 4 x 10 13 protons/s (8 GeV) and high Z target. a proton current of 4 x 10 13 protons/s (8 GeV) and high Z target. Curved transport selects low momentum   (n,  removed)Curved transport selects low momentum   (n,  removed) High rate capability electron detectors in a 1 T fieldHigh rate capability electron detectors in a 1 T field Crystal Calorimeter Straw Tracker Stopping Target Foils Pion Production Target Superconducting Solenoids Proton Beam Muon Beam 5 T5 T 2. 5 T 2 T2 T 1 T1 T 1 T1 T

18. 12 Sepetmber 2008 Paolo Walter Cattaneo 18 MECO/MU2E proton beam Pulsed beam from AGS (BNL)/FERMILAB to reduce prompt backgrounds. Measurement window

19. 12 Sepetmber 2008 Paolo Walter Cattaneo 19 MECO/MU2E expected sensitivity Expected  5 signal events for 10 7 s (2800 hours) running if R  e = 10 -16 0.60  capture probability 5.0 Detected events for R  e = 10 -16 0.19 Fitting and selection criteria efficiency 0.90 Electron trigger efficiency 0.49 0.49 Fraction of  capture in detection time window 0.58  stopping probability 0.0043  entering transport solenoid / incident proton 4  10 13 Proton flux (Hz) (50% duty factor, 740 kHz micropulse) 10 7 Running time (s) Factor Contributions to the Signal Rate Expected ~ 0.45 bck events (0.25 MIO, 0.07 RPC) for 10 7 s running time.

20. 12 Sepetmber 2008 Paolo Walter Cattaneo 20 PRISM/PRIME PRIsm Muon Electron conversion experiment Phase Rotation Intense Slow Muon source (FFAG) At JPARC (Japan) Fixed Field Alternating Gradient (FFAG) synchrotron ready in 2007 High intensity pulsed proton beam (~ 10 14 p/s); High intensity pulsed proton beam (~ 10 14 p/s);  Muon energy spread reduction (phase rotation)   E 2  3% FWHM spread (phase rotation)   E 2  3% FWHM spread  Intensity  10 12  /s (no pions);  Muon momentum 68 MeV/c. Small  E essential to stop enough muons in very thin targets, improving momentum resolution. If  p  350 keV (FWHM), the experiment can be sensitive to BR(  e)< 10 -(18  19).

21. 12 Sepetmber 2008 Paolo Walter Cattaneo 21 PRIME Detector Layout PRIME= PRISM mu-e conversion –High field solenoid magnet –Target –Positron tracking chambers –Positron energy calorimeter

22. 12 Sepetmber 2008 Paolo Walter Cattaneo 22 A look at the future High intensity machines under study (like NUFACT at CERN or Proton Driver at Fermilab) should provide proton beams at the level of 10 15 protons/s of some GeV. Secondary beams with intensity ~ 10 14  /s could be obtained from these machines. The   A -> e - A conversion experiments are not limited by accidental background. In principle they can benefit of the increased muon beam intensity much better than  -> e  experiments. We can hope to gain a couple of order of magnitudes in the experimental sensitivity for LFV muon decays in respect with present experiments ?

23. 12 Sepetmber 2008 Paolo Walter Cattaneo 23  - A   - A,X The possibility of exploring  A,X conversion channel is under investigation It could complement the LFV  decays, as ,  e  etc.  Need of an intense high energy muon beam: a) E   20 GeV b) 10 20 muons/year (  /neutrino factory ) a) E   20 GeV b) 10 20 muons/year (  /neutrino factory )   production compatible with existing bounds: up to several thousands of  ’s (depending on  energy)  Signal selection based on angular distribution of  decay products (hard hadrons or  ) and missing momentum decay products (hard hadrons or  ) and missing momentum Backgrounds: mis-identified hard  from  A   A’, hard hadrons from target Backgrounds: mis-identified hard  from  A   A’, hard hadrons from target  Need of realistic MC simulations and detector design !

24. 12 Sepetmber 2008 Paolo Walter Cattaneo 24 The tauonic channel

25. 12 Sepetmber 2008 Paolo Walter Cattaneo 25 Generalities The  channel is in principle very interesting for studying LFV because of the  large mass (m   17 m  )  Many decay channels;  BR’s enhanced in respect with   e  by (m  /m  )  with  ~ 3 Experimental problem: production & detection of  large samples. To be competitive with dedicated experiments one must reach BR(  ) < 10 -(8  ) Significant improvements obtained by B-factories (BELLE,BABAR).

26. 12 Sepetmber 2008 Paolo Walter Cattaneo 26 Predicted by many new physics models –Normal NP models enhance    and    l + l - –Some NP models may enhance other modes –    e  and    el + l are similar Several measurable BR O(10 -8 ) in parameter space. Reference      SM+ mixing EPJ C8(1999)51310 -40 10 -14 SM + heavy Maj R PRD 66(2002)03400810 -9 10 -10 Non-universal Z’PLB 547(2002)25210 -9 10 -8 SUSY SO(10)PRD 68(2003)03301210 -8 10 -10 mSUGRA+seesawPRD 66(2002)11501310 -7 10 -9 SUSY HiggsPLB 566(2003)21710 -10 10 -7 LFV  decays: prediction

27. 12 Sepetmber 2008 Paolo Walter Cattaneo 27 SUSY predictions for  LFV decays Green: Belle (2008) Yellow: BaBar (2008) Br(    ee) / Br(    )  1/94 Br(    )/ Br(    )  1/440 Br(   eee) / Br(   e  )  1/94 Br(   e  )/ Br(   e  )  1/440 B-factories are  -factories too B-factories are  -factories too:   e 

28. 12 Sepetmber 2008 Paolo Walter Cattaneo 28    qq _ 2photon process  f=leptons,quarks signal Only tag side has neutrino(s). Both sides have neutrino(s). radiative Bhabha process e+e+ ee ee ee ee ee  many tracks e + e -      –1 prong tau decay (BR~85%) LFV  decays; Signal and Background

29. 12 Sepetmber 2008 Paolo Walter Cattaneo 29 Current status of LFV search

30. 12 Sepetmber 2008 Paolo Walter Cattaneo 30 Int. Luminosity at B-factories >1.3 ab - 1 –~1.2x10 9  -pairs Super B-factory 10 ab - 1 /year (50 ab - 1 ) BR sensitivity –It depends on background. –   l  ; scale as ~1/  L e  e        is irreducible BG. ~10 -8 level at super B-factory –   lll, lX 0 ; scale as ~1/L O(10 -9 ) level at super B-factory The future: Super B factories Super-B factories are under design: luminosity 5 x 10 35 cm -2 s -1

31. 12 Sepetmber 2008 Paolo Walter Cattaneo 31 The future: LHC LHC In one year of data taking at low luminosity, ~ 10 12  are produced and several hundred millions could be used to search for LFV  decays. Main  sources:W -> , Z ->    , B ->  D The predicted sensitivities in the  ->  and  -> 3  channels are Brs ~ 10 -7- 10 -8, at the level of the present B-factories results (the  -> 3  channel has the best signal/noise ratio).

32. 12 Sepetmber 2008 Paolo Walter Cattaneo 32 Existing LFV limits starts challenging New Physics model. The strongest constraint from: –Br(  ->e  ) < 1.2 10 -11 –Br (  ee ) < 2.0 10 -8 MEG plans to reach in the next few years –Br(  ->e  ) < 1.0 10 -13 Similar constraints from SuperB factory –Br (  lll ) < 1.0 10 -9 Strongest limit from  ->eA (Mu2e-PRISME) –Br(  ->e  ) < 1.0 10 -17-18 In future  -factory could bring farther improvement down to Br(  ->e  ) < 1.0 10 -19-20 Summary

33. 12 Sepetmber 2008 Paolo Walter Cattaneo 33 On Demand

34. 12 Sepetmber 2008 Paolo Walter Cattaneo 34 Many possibilities … Second Higgs Heavy Z’, Anomalous Z coupling Supersymmetry Heavy Neutrinos Leptoquarks After W. Marciano Predictions at 10 -15

35. 12 Sepetmber 2008 Paolo Walter Cattaneo 35 Most famous SM extension LFV are generated through slepton mixing. –Independent parameter for   e  SUSY seesaw (J.Hisano et. al.,PRD 60 (1999) 055008) –Achievable BR of O(10 -7~-8 ) if tan  ~60 and m SUSY ~1TeV/c 2 SUSY

36. 12 Sepetmber 2008 Paolo Walter Cattaneo 36 When sleptons are heavy (>weak scale), Br(    ) is suppressed. Higgs in SUSY enhances other LFV modes, such as   3l, l+hadrons,... Higgs-mediated MSSM –   3  (A.Brignole, A.Rossi, PLB 566 (2003) 217) –Enhanced if tan  is large and Higgs mass is small. SUSY Higgs

37. 12 Sepetmber 2008 Paolo Walter Cattaneo 37 SUSY Higgs Higgs-mediated MSSM (M.Sher, PRD 66 (2002) 057301) –Br(    ) : Br(    ) = 8.4 : 1 Phase space, color factor, mass MSSM seesaw (E.Arganda, arXiv:0803.2039v1) –Large BR of O(10 -7 ) for   ,  ’,     Need to search for all possible LFV modes –To probe unknown physics and discriminate models

38. 12 Sepetmber 2008 Paolo Walter Cattaneo 38 38  decay in vacuum: E e < m  c 2 /2  decay in bound orbit: E e < m  c 2 - E NR - E B Radiative Muon Capture:  - N   N(Z-1)  For Al, E  max =102.5 MeV/c 2, P(E  >100.5 MeV/c 2 ) =4  10 -9 P(   e + e -, E e > 100.5 MeV/c 2 ) = 2.5  10 -5 Restricts choice of stopping targets: M z-1 > M z Radiative Pion Capture:  - N  N(Z-1)  Branching fraction ~ 1.2% for E  > 105 MeV/c 2 P(   e + e -, 103.5 < E e < 100.5 MeV/c 2 ) = 3.5  10 -5 Limits allowed pion contamination in beam during detection time  - A  e - A: Signal and Background

39. 12 Sepetmber 2008 Paolo Walter Cattaneo 39 MECO expected sensitivity Expected ~ 5 signal events for 10 7 s (2800 hours) running if R  e = 10 - 16 0.60  capture probability 5.0 Detected events for R  e = 10 -16 0.19 Fitting and selection criteria efficiency 0.90 Electron trigger efficiency 0.49 0.49 Fraction of  capture in detection time window 0.58  stopping probability 0.0043  entering transport solenoid / incident proton 4  10 13 Proton flux (Hz) (50% duty factor, 740 kHz micropulse) 10 7 Running time (s) Factor Contributions to the Signal Rate

40. 12 Sepetmber 2008 Paolo Walter Cattaneo 40 MECO background Without scattering in stopping target < 0.03  decay in flight Assuming 10 -4 CR veto inefficiency 0.004 Cosmic ray induced Mostly from  - 0.007 Anti-proton induced Assuming 10 -9 inter-bunch extinction 0.45 Total Background From late arriving pions 0.001 Radiative  capture From out of time protons 0.07 Radiative  capture < 0.001  decay in flight With scattering in stopping target 0.04 0.04  decay in flight < 0.04 Beam e - < 0.005 Radiative  decay < 0.006 Tracking errors S/N = 20 for R  e = 10 -16 0.25  decay in orbit CommentsEventsSource Expected ~ 0.45 bck events for 10 7 s running time.

41. 12 Sepetmber 2008 Paolo Walter Cattaneo 41 A look at the future: rough estimate for a possible pulsed muon beam at NUFACT or Fermilab Proton Driver Using MECO numbers for scaling: MECO Proton Driver NUFACT MECO Proton Driver NUFACT  p/s (8 GeV) 4 x 10 13 1  2 x 10 15 1.5 x 10 15   /s (tungsten target) 1 x 10 11 3  5 x 10 11 1 x 10 12  Sensitivity 2 x 10 -17 few x 10 -18 1 x 10 -18 Competitive with PRIME. Competitive with PRIME. (same extinction factor assumed: 10 9 )  Power release: ~ 10 kW many tens of kW ~ 100 kW (need of target cooling to avoid melting) (need of target cooling to avoid melting) Need precise design and estimates. E p = 2.2 GeV; scaling by using GHEISHA. E p = 2.2 GeV; scaling by using GHEISHA.

42. 12 Sepetmber 2008 Paolo Walter Cattaneo 42 Beam requirements for   e  Continuous beam to reduce the accidental background; Continuous beam to reduce the accidental background; Small momentum bite (  p/p  10 %) to use thin targets; Small momentum bite (  p/p  10 %) to use thin targets; Use surface muons (p s = 29 MeV/c) to maximize the pion stopping Use surface muons (p s = 29 MeV/c) to maximize the pion stopping rate in the target (R  p 3.5 for p  p s ); rate in the target (R  p 3.5 for p  p s ); Good  /e separation by Wien filters; Good  /e separation by Wien filters; Possible solution to realize an (almost) continuos muon beam: Possible solution to realize an (almost) continuos muon beam: insert a thin (~ 10 -3 interaction lengths) pion production insert a thin (~ 10 -3 interaction lengths) pion production target inside the proton synchrotron or recirculating LINAC. target inside the proton synchrotron or recirculating LINAC. Protons recirculate many times and end up interacting. Protons recirculate many times and end up interacting. If they stay in the synchrotron/LINAC for a long time, If they stay in the synchrotron/LINAC for a long time, an almost continuous muon beam can (in principle) be obtained. an almost continuous muon beam can (in principle) be obtained. Problems: - target heating; Problems: - target heating; - radiation in the target area (safety requirements). - radiation in the target area (safety requirements). See J. Äystö et al., “Physics with low-energy muons at a neutrino See J. Äystö et al., “Physics with low-energy muons at a neutrino factory complex”, hep-ph/0109217 factory complex”, hep-ph/0109217

43. 12 Sepetmber 2008 Paolo Walter Cattaneo 43 Conclusions about   e   The MEG experiment at PSI is in advanced state of building and testing; the data taking is foreseen for 2006. testing; the data taking is foreseen for 2006.  The expected MEG sensitivity is down to BR(  e  )  10 -13, a two orders of magnitude improvement in respect with a two orders of magnitude improvement in respect with present bound. Many SUSY models predict LFV in the present bound. Many SUSY models predict LFV in the  e  channel at this level or even higher.  e  channel at this level or even higher.  A further improvement in sensitivity by using more intense muon beams is not easy because of accidental background muon beams is not easy because of accidental background limitations; strong improvements in detector technologies limitations; strong improvements in detector technologies are needed. Moreover, a continuous beam must be realized. are needed. Moreover, a continuous beam must be realized.

44. 12 Sepetmber 2008 Paolo Walter Cattaneo 44 Conclusions about  - A  e - A conversion  The  - A  e - A conversion BR is predicted by many SUSY theories at measurable levels (~ 10 -15 ). The  - A  e - A conversion and the at measurable levels (~ 10 -15 ). The  - A  e - A conversion and the  e  channels are complementary in discriminating between  e  channels are complementary in discriminating between LFV theoretical models. LFV theoretical models.  Two LFV experiments working in the  - A  e - A conversion channel are in preparation/project: MECO and PRIME; results are are in preparation/project: MECO and PRIME; results are expected in some years from now. They should improve the expected in some years from now. They should improve the present limit on the  - A  e - A BR (~ 10 -13 ) by at least present limit on the  - A  e - A BR (~ 10 -13 ) by at least three orders of magnitude. three orders of magnitude.  Since they are not limited by accidental background,  - A  e - A conversion experiments can potentially benefit from the muon conversion experiments can potentially benefit from the muon flux increase expected in Neutrino Factories and Muon Facilities. flux increase expected in Neutrino Factories and Muon Facilities.  The key factors are momentum resolution and pion extinction factor. A suitably tuned pulsed muon beam is needed. factor. A suitably tuned pulsed muon beam is needed.

45. 12 Sepetmber 2008 Paolo Walter Cattaneo 45 Conclusions about muonic channel   e  - The MEG experiment at PSI is in advanced state of building and testing; data taking - The MEG experiment at PSI is in advanced state of building and testing; data taking is foreseen for 2006. The expected MEG sensitivity is down to BR(  e  )  10 -13, is foreseen for 2006. The expected MEG sensitivity is down to BR(  e  )  10 -13, a two orders of magnitude improvement in respect with present bound. Many SUSY a two orders of magnitude improvement in respect with present bound. Many SUSY models predict LFV in the  e  channel at this level or even higher. models predict LFV in the  e  channel at this level or even higher. - A further improvement in sensitivity by using more intense  -beams is not easy - A further improvement in sensitivity by using more intense  -beams is not easy because of accidental background limitations; strong improvements in detector because of accidental background limitations; strong improvements in detector technologies are needed; a continuous beam must be realized. technologies are needed; a continuous beam must be realized.   - A  e - A - The  - A  e - A conversion and the  e  channels are complementary in - The  - A  e - A conversion and the  e  channels are complementary in discriminating between LFV theoretical models. Two  - A  e - A conversion discriminating between LFV theoretical models. Two  - A  e - A conversion experiments are in preparation/project: MECO and PRIME; results are experiments are in preparation/project: MECO and PRIME; results are expected in some years from now. They should improve the present limit expected in some years from now. They should improve the present limit on the  - A  e - A BR (8 x10 -13 ) by at least three orders of magnitude. on the  - A  e - A BR (8 x10 -13 ) by at least three orders of magnitude. - Since they are not limited by accidental background,  - A  e - A conversion - Since they are not limited by accidental background,  - A  e - A conversion experiments can potentially benefit from the muon flux increase expected in experiments can potentially benefit from the muon flux increase expected in Neutrino Factories and Muon Facilities. The key factors are momentum resolution Neutrino Factories and Muon Facilities. The key factors are momentum resolution and pion extinction factor. A suitably tuned pulsed muon beam is needed. and pion extinction factor. A suitably tuned pulsed muon beam is needed.

46. 12 Sepetmber 2008 Paolo Walter Cattaneo 46 Conclusions on tauonic channel  The tauonic channel is very promising for the search for LFV processes because the large  mass enhances the BR’s and opens a lot of possible channels. Experimentally speaking, this channel is presently not yet competitive (but not so far) from the more studied muonic channel.  The B-factory experiments improved the limits on  LFV decay BR’s by about one order of magnitude; one or two other order of magnitudes should be gained by Super B-factories, reaching BR levels which would put severe constraints on supersymmetric parameter space. To fully benefit of the increase in luminosity, a careful background control is needed.  Huge samples of  ’s will be produced at LHC, even at low luminosity, but only a sub-sample can be used for LFV studies. LFV decays of SUSY particles can be studied together with “usual” LFV  decays.