1. -LFV and related topics
M. Grassi – INFN Pisa Rome - November 7th , 2005

2. M. Grassi – INFN Pisa Rome - November 7th , 2005
Requests
We were asked of focusing on the following items
Physics motivation
Technology aspects
Cost estimates
Manpower
Interest in Italy
… but I’ll discuss mainly the mLFV  x ~
M. Grassi – INFN Pisa Rome - November 7th , 2005

3. Examples of CLFV processes
NeN’
ee
 -LFV
tlll
t l
t lp / lh / lh’
m N  t N’ X
K system
KL  e
KL  p0e
K±  p ± e
Precise measurements
-EDM
g-2
 decay parameters
M. Grassi – INFN Pisa Rome - November 7th , 2005

4. Physics motivation they are experimentally accessible
Charged Lepton Flavour Violation (CLFV) processes, like meg , meee , me conversion, and also teg , t m g , tlll , are negligibly small in the extended Standard Model (SM) with massive Dirac neutrinos (BR  10-50)
Super-Symmetric extensions of the SM (SUSY-GUTs) with right handed neutrinos and see-saw mechanism may produce CLFV processes at significant rates
CLFV decays are therefore a clean (no SM contaminated) indication of profound New Physics (mainly SUSY, but also on other exotic scenarios )
and
they are experimentally accessible
M. Grassi – INFN Pisa Rome - November 7th , 2005

5. Model independent indications
Mag. Mom. Trans.
Direct violat
Effective interactions:
Dependence upon arbitrary parameters  and F
M. Grassi – INFN Pisa Rome - November 7th , 2005

6. Model independent indications
The same effective interaction
implies also
a non zero mEDM and
deviations for the muon gm-2 value with respect to the SM predictions
M. Grassi – INFN Pisa Rome - November 7th , 2005

7. SUSY indications for meg
LFV induced by finite slepton mixing through radiative corrections
Experimental limit
SUSY SU(5) predictions
BR (meg)   10-13
SUSY SO(10) predictions
BRSO(10)  100 BRSU(5)
R. Barbieri et al., Phys. Lett. B338(1994) 212
R. Barbieri et al., Nucl. Phys. B445(1995) 215
small tan(b) excluded by LEP results
M. Grassi – INFN Pisa Rome - November 7th , 2005

8. n-oscillation connection
Additional contribution to slepton mixing from V21 (the matrix element responsible for solar neutrino deficit)
Experimental limit
tan(b)=30
tan(b)=1
J. Hisano, N. Nomura, Phys. Rev. D59 (1999)116010
M. Grassi – INFN Pisa Rome - November 7th , 2005

9. The muon trio gm-2 meg me conv mEDM
In SUSY models the slepton mixing matrix links the three processes
gm-2
meg
me conv
mEDM
L. Roberts
Y. Kuno
M. Grassi – INFN Pisa Rome - November 7th , 2005

10. M. Grassi – INFN Pisa Rome - November 7th , 2005
SU(5) LFV ratios
10-11
m<0
m>0
On large classes of
SUSY-GUT
BR(m-e conv)  10-2 BR(meg)
BR(m3e)  10-2 BR(meg)
BR(t mg)  10+5 BR(meg)
m-e:Ti conv
10-20
meg
J.Hisano et al., Phys.Lett. B391(1997)341
10-20
M. Grassi – INFN Pisa Rome - November 7th , 2005

11. M. Grassi – INFN Pisa Rome - November 7th , 2005
CLFV comparison
BR(tmg) x 108
102
103
BR(meg) x 1012
10-2
Within the same, or among different unification models the predictions of CLFV processes have large variations
J.Ellis et al., Eur.Phys.J. C14(2000)319
M. Grassi – INFN Pisa Rome - November 7th , 2005

12. M. Grassi – INFN Pisa Rome - November 7th , 2005
Predictions ?
Huge spread of SUSY prediction – 10-19
In R-violating SUSY the dominant process are m3e and m-e conv
Super Symmetry does not exist...
Extra dimensions theories have parameters values with measurable BR
Choice based on feasibility arguments
M. Grassi – INFN Pisa Rome - November 7th , 2005

13. Experimental situation
LFV searches
Orders of magnitude improvement
are required:
experimental challenge!
M. Grassi – INFN Pisa Rome - November 7th , 2005

14. M. Grassi – INFN Pisa Rome - November 7th , 2005
m sector
3e
e
NeN’
-EDM
g-2
ee
dedicated beams
dedicated experiments
single purpose
M. Grassi – INFN Pisa Rome - November 7th , 2005

15. M. Grassi – INFN Pisa Rome - November 7th , 2005
+e+e+e-
background
signal
  eee
accidental
  e n n
e+e- e+e-
e + e+ e-
correlated
  e e e n n
e+ + n e- e+
e+ + n
Coplanarity
Vertexing
Ee = m
Te+ = Te+ = Te- + n e+ e-
M. Grassi – INFN Pisa Rome - November 7th , 2005

16. +e+e+e- : SINDRUM I Present limit B(m3e ) < 1x10-12
U.Bellgardt et al. Nucl.Phys. B299(1988)1
No other experimental proposal
This channel has only charged particles in the final state
The experiment needs only a tracking system but
Sustain the entire Michel decay rate
Down to low momentum
4p coverage
SINDRUM I parameters
beam intensity 6x106 m+/s
m+ momentum 25 MeV/c
magnetic field 0.33T
acceptance 24%
momentum res. 10% FWHM
vertex res.  2 mm2 FWHM
timing res.  ns
target length 220 mm
target density 11 mg/cm2
M. Grassi – INFN Pisa Rome - November 7th , 2005

17. M. Grassi – INFN Pisa Rome - November 7th , 2005
+e+e+e- : future
SINDRUM: sensitivity  10-12
background  10-13
A new experiment should aim to a sensitivity: B  10-16
would require  109 m+/s but
background  (6 order of magnitude !)
Exercise: detector improvements for just a 104 factor
momentum resolution 10% FWHM  1% FWHM
bckg scales quadratically with momentum resolution
co-planarity test ?
vertex resolution 2 mm2  <1 mm2
target length 220 mm  ?
target density 11 mg/cm2  ?
timing resolution  ns   100 ps
(accidental background increases quadratically with the muon stop rate)
M. Grassi – INFN Pisa Rome - November 7th , 2005

18. M. Grassi – INFN Pisa Rome - November 7th , 2005
+e+e+e- : summary
No other experimental proposal
Six orders of magnitude of background reduction are required
four orders of magnitude could be achieved, two more?
This is not a relevant item
M. Grassi – INFN Pisa Rome - November 7th , 2005

19. M. Grassi – INFN Pisa Rome - November 7th , 2005
background
signal
  e g
accidental
  e n n
  e g n n
ee  g g
eZ  eZ g
correlated physical
  e g n n
e+ + g
e+ + g n
e+ + n
qeg = 180°
Ee = Eg = 52.8 MeV
Te = Tg g
M. Grassi – INFN Pisa Rome - November 7th , 2005

20. M. Grassi – INFN Pisa Rome - November 7th , 2005
+e+ : present
Present limit B(e) < 1.2x10-11 by the MEGA Collab.
M.L.Brooks et al. Phys.Rev.Lett. 83(1999)1521
Near to start data-taking experiment: MEG
M. Grassi – INFN Pisa Rome - November 7th , 2005

21. +e+ : MEG experimental method
Easy signal selection with + at rest
Detector outline
Stopped beam of 3x107  /sec in a 150 mm target
Liquid Xenon calorimeter for  detection (scintillation)
fast: 4 / 22 / 45 ns
high LY: ~ 0.8 * NaI
short X0: 2.77 cm
Solenoid spectrometer & drift chambers for e+ momentum
Scintillation counters for e+ timing
e+ + g
Ee = Eg = 52.8 MeV
qeg = 180°
M. Grassi – INFN Pisa Rome - November 7th , 2005

22. +e+ : MEG required performances
The sensitivity is limited by the by the accidental background
The  310-14
allows BR (meg)  but needs
FWHM
Exp./Lab
Year
DEe/Ee
(%)
DEg /Eg
Dteg (ns)
Dqeg
(mrad)
Stop rate
(s-1)
Duty cyc.(%) BR
(90% CL)
SIN
1977
8.7
9.3
1.4 -
5 x 105
100
3.6 x 10-9
TRIUMF 10
6.7
2 x 105
1 x 10-9
LANL
1979
8.8 8
1.9 37
2.4 x 105
6.4
1.7 x 10-10
Crystal Box
1986
1.3 87
4 x 105
(6..9)
4.9 x 10-11
MEGA
1999
1.2
4.5
1.6 17
2.5 x 108
(6..7)
1.2 x 10-11
MEG
2006
0.8 4
0.15 19
2.5 x 107
1 x 10-13
M. Grassi – INFN Pisa Rome - November 7th , 2005

23. +e+ : correlated background
The correlated background is smaller than the accidental one
The correlated background
has a complicate dependence on the photon (y) and positron (x) energy resolutions.
Its rate depends linearly on the R
The BR is 3x10-15
M. Grassi – INFN Pisa Rome - November 7th , 2005

24. +e+ : MEG sensitivity summary
Cuts at 1,4FWHM
Detector parameters
Signal
 410-14
Single Event Sensitivity
 310-14
 310-15
Backgrounds
Upper Limit at 90% CL BR (meg)  110-13
Discovery events (P = 210-3) correspond BR = 210-13
M. Grassi – INFN Pisa Rome - November 7th , 2005

25. +e+ : MEG time profile
Planning
R & D
Assembly
Data Taking
now
LoI
Proposal
Revised
document
More details at
M. Grassi – INFN Pisa Rome - November 7th , 2005

26. M. Grassi – INFN Pisa Rome - November 7th , 2005
+e+ summary
The PSI E5 can deliver up to 3x108 +/s
The MEG sensitivity is accidental background limited
With better detector resolutions a BR of would be possible
No need, at least for the next 10 years, for a more intense beam
M. Grassi – INFN Pisa Rome - November 7th , 2005

27. M. Grassi – INFN Pisa Rome - November 7th , 2005
+e+ comments
Total MEG cost: 7.5 M€
At the limit of present-day technology
Detector completion in spring 2006
Engineering runs 2006
Full statistic 3 years
A few months data taking for a factor 10 improvement (2007)
Italian collaboration: 4 groups fully committed (adding up ~20 fte)
Near future:
Detector improvement
Polarized m beam (in case of signal !)
M. Grassi – INFN Pisa Rome - November 7th , 2005

28. -e- conversion background Signal Ee = mm -EB -ER  (A,Z)  e (A,Z)
coherent LFV decay
 (A,Z)  e (A,Z)
RPC (radiative pion capture)
 (A,Z)   (A,Z-1)
e- - g
(A,Z) - g
(A,Z)
MIO (muon decay in orbit)
 (A,Z)  e n n (A,Z)
Ee = mm -EB -ER
e- - n
(A,Z)
M. Grassi – INFN Pisa Rome - November 7th , 2005

29. -e- generalities
1 particle in the final state: no accidental Background
chance for pushing down the limit on BR
Event selection based on e- momentum only
m lifetime ~.9 ms on Al or .35 ms on Ti
Key element: beam quality !
Short (dt ~ 10ns) and intense (~ 1013 m/s) pulses of low momentum m (~ 68 MeV/c)
Long beam off intervals ( Dt ~ 1 ms )
Extremely low p contamination (10-9 proton extinction or FFAG)
Narrow momentum spread (<2 % with FFAG)
M. Grassi – INFN Pisa Rome - November 7th , 2005

30. M. Grassi – INFN Pisa Rome - November 7th , 2005
-e- : sensitivity
R.Kitano et al Phys.Rev.D66(2002)096002
M. Grassi – INFN Pisa Rome - November 7th , 2005

31. M. Grassi – INFN Pisa Rome - November 7th , 2005
-e- conv. present
Present limit B(me:Au ) < 8x by the SINDRUM II
A. Van der Schaaf, NOON03
New approved experiment: MECO B(me) < (2008 ? )
New project LOI to J-PARC: PRISM/PRIME B(me) < (>2010 ? )
cancelled
M. Grassi – INFN Pisa Rome - November 7th , 2005

32. -e- : SINDRUM II result
SINDRUM II parameters
beam intensity 3x107 m-/s
m- momentum 53 MeV/c
magnetic field 0.33T
acceptance 7%
momentum res. 2% FWHM
S.E.S 3.3x10-13
B(me:Au ) 8x10-13
M. Grassi – INFN Pisa Rome - November 7th , 2005

33. M. Grassi – INFN Pisa Rome - November 7th , 2005
-e- : PRISM beam
Phase Rotated Intense Slow Muon source
To be operated at J-PARC (Japan)
or elsewhere !!! (if J-PARC …)
Based on a FFAG ring
FFAG funded by Osaka Univ.
Ready end 2007
M. Grassi – INFN Pisa Rome - November 7th , 2005

34. M. Grassi – INFN Pisa Rome - November 7th , 2005
-e- : PRISM beam
Muon momentum spread reduction by phase rotation down to 2  3 % FWHM
Intensity  1012 m/s (no pions);
Muon momentum 68 MeV/c.
The small energy spread allows very thin targets (<100 mm)
If a momentum resolution  350 keV FWHM is reached, the experiment could be sensitive to m  e conversion with
SES ~ 6x10-19
BR ~ 10-18
Phase rotation concept
M. Grassi – INFN Pisa Rome - November 7th , 2005

35. M. Grassi – INFN Pisa Rome - November 7th , 2005
-e- : PRIME detector
Only a LOI has been presented at J-PARC
The detector is in form of conceptual design
The Collaboration seed is formed by Jap and US researchers
Cost ???
Timescale ???
The physics channel is a very challenging but really interesting
M. Grassi – INFN Pisa Rome - November 7th , 2005

36. -e- and +e+ as probes of New Physics
me conv. is more sensitive for all processes not mediated by photon
e is more sensitive for processes mediated by photons
The motivation is sufficiently strong that both experiments should be done
Relative rates for e and me conv. would give information on underlying mechanism
A significant rate for e with polarized muons could give additional information on mechanism
M. Grassi – INFN Pisa Rome - November 7th , 2005

37. gm-2 and e+e- based prediction
All E821 results were obtained with a “blind” analysis.
~2.7s difference with e+e- based SM prediction
world average
M. Grassi – INFN Pisa Rome - November 7th , 2005

38. Future gm-2 experiments
Leading role of US groups
BNL 0.5 → 0.20 ppm (scientific approval but not funded)
expected near-term improvement in theory, → the ability to confront the SM by ~ x 2
The next generation 0.20 → 0.06 ppm
substantial R&D would be necessary
M. Grassi – INFN Pisa Rome - November 7th , 2005

39. A gm-2 experiment to ~0.06 ppm?
Makes sense if the theory can be improved to 0.1 ppm, which is hard, but maybe not impossible.
With the present storage ring, we already have
M. Grassi – INFN Pisa Rome - November 7th , 2005

40. M. Grassi – INFN Pisa Rome - November 7th , 2005
The Physics Case
Scenario 1
LHC finds SUSY
MEG sees m → e g
The trio will have SUSY enhancements
to understand the nature of the SUSY space we need to get all the information possible to understand the nature of this new theory
a la L. Roberts
M. Grassi – INFN Pisa Rome - November 7th , 2005

41. M. Grassi – INFN Pisa Rome - November 7th , 2005
The Physics Case
Scenario 2
LHC finds Standard Model Higgs at a reasonable mass, nothing else …
Then precision measurements come to the forefront, since they are sensitive to heavier virtual particles.
μ-e conversion is especially sensitive to other new physics besides SUSY
a la L. Roberts
M. Grassi – INFN Pisa Rome - November 7th , 2005

42. M. Grassi – INFN Pisa Rome - November 7th , 2005
Muon EDM
Present limit ~10-19 e-cm
Could reach at a high intensity muon source
Developments and technology owned by US groups
We could think of placing the ring not in the USA! J-PARC already was thought as an opportunity
M. Grassi – INFN Pisa Rome - November 7th , 2005

43. M. Grassi – INFN Pisa Rome - November 7th , 2005
Muon channel
Realm of an other WG …
M. Grassi – INFN Pisa Rome - November 7th , 2005

44. M. Grassi – INFN Pisa Rome - November 7th , 2005
Conclusion
 are sensitive probes of physics beyond the Standard Model
SUSY theories require cLFV not far from present existing upper limits
Strong case for experimental searches in all channels, together with improved measurement of gm-2 and mEDM
+e+ results are expected in 2007
-e- conversion search is planned at the level of 10-18
-e- conversion is not accidental background limited could benefit of new high intensity pulsed beams
M. Grassi – INFN Pisa Rome - November 7th , 2005

45. M. Grassi – INFN Pisa Rome - November 7th , 2005
Bibliography
General
J.Aysto et al. CERN-TH/
NuFact03 proceedings
INFN WG 2004
SINDRUM coll., W Bertl et al. Nucl.Phys. B260(1988)1
SINDRUM2 coll., W Honecker et al. Phys.Rev.Lett. 76(1996)200
MECO coll., BNL proposal AGS P940 (1997)
MEG coll., “The MEG proposal” (2002)
m-A  t-A,X
S.N. Gninenko et al.,Mod. Phys. Lett. A17 (2002) 1407,
M. Sher et al.,Phys. Rev. D69 (2004) )
M. Grassi – INFN Pisa Rome - November 7th , 2005