1. LEPTON-FLAVOUR VIOLATION AND NEUTRINO OSCILLATIONS
Carlo Bemporad
Venezia 5/12/2003
LEPTON-FLAVOUR VIOLATION AND NEUTRINO OSCILLATIONS
The MEG Experiment at PSI
Non ancora a presentazione definitiva

2.   e g An experiment which was repeated many times, each time
with improved sensitivity (about a factor of 100/decade)
Like the measurement of the  (g-2), it provided, several times,
important constraints to theory
Lepton-flavour violation experiments which are closely related:
Muon-electron conversion in a muonic atom
Muon-decay into three electrons
Muonium-Antimuonium conversion

3. if equal, THEORY: (  e g)/TOT branching ratio  10-4
HISTORY
neutrino hypothesis for -decay Pauli (1930)
weak interaction theory Fermi (1934)
proposed method for n detection Pontecorvo (1946)
ne discovery Reines and Cowan (1956)
DOES A   e EXISTS ?
if equal, THEORY: (  e g)/TOT branching ratio  10-4
Feinberg (1958), Gell-Mann and Feynman (1958)
EXPERIMENTS:
no gammas Hincks and Pontecorvo (1947)
B< % C.L. Berley, Lee, Bardon (1959)
B< C.L Frankel et al. (1962)
B< C.L Bartlett, Devons, Sachs (1962)
………………………………(1999) MEGA B<
Experiment by Danby at al. directly proves   e (1962)

4. Previous measurements and related experiments
SUMMARY
Physics motivations
Previous measurements and related experiments
General description of the MEG experiment
The New Liquid Xenon Calorimetry
Test Beam verification of detector performances
Achievable sensitivity and time schedule

5. LEPTON FLAVOUR VIOLATION IS NOW AN ESTABLISHED FACT !
Atmospheric, accelerator, solar, reactor neutrino oscillations
First measurement of some mixing parameters
BEYOND THE STANDARD MODEL
New experiments in Neutrino Physics, under way or close by,
on Neutrino Oscillations, Double  Decay, etc.
but after a decade of great advances
one probably needs new facilities
Superbeams, Large-Mass Exps., Neutrino Factories…..
While waiting for them
LOOK AT SIMPLE PROCESSES IN WHICH
THE “NEW PHYSICS” CAN MANIFEST ITSELF
(Constraints to Theory even if the e decay is not seen !)

6. SUGRA indications SUSY SU(5) predictions BR (e)  10-14  10-13
LFV induced by finite slepton mixing through radiative corrections
Our goal
Experimental limit
SUSY SU(5) predictions
BR (e)   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
combined LEP results favour tan>10

7. Combined LEP experiments: SUGRA MSSM

8. SO10
Kuno, Okada
Rev.Mod.Phys. 73, 151 (2001)

9. CONNECTIONS WITH NEUTRINO-OSCILLATIONS
J. Hisano, N. Nomura, Phys. Rev. D59 (1999)
Additional contribution to slepton mixing from V21 (the matrix element responsible for solar neutrino deficit)
Our goal
Experimental limit
tan(b)=30
tan(b)=1
After SNO
After Kamland
in the Standard Model !

10. Vast Recent Literature on SUSY and Connection between
Neutrino-oscillations, LFV rare decays, EDM, g-2.
Examples:
Hisano, Nomura, PRD 59, (1999) Casas, Ibarra, hep-ph
Lavignac, Masina, Savoy, hep-ph/ Babu, Pati, hep-ph/
Raidal, Strumia, PLB 553, 72 (2003) Barr, hep-ph/
Blažek, King, NPB 662, 359 (2003) Masiero, Vempati, hep-ph/
Petcov, Profumo, Takanishi, Yaguna, NPB9187 in press
Rather technical papers
Constraints from new experimental information
Even the full knowledge of neutrino masses and mixing angles
is able to determine the seesaw parameters like: the neutrino
Yukawa coupling h and the heavy right-handed neutrino
Maiorana mass MR (and therefore e…).
Complementary informations. (Masiero, Vempati hep-ph/ )
Predictions for measurable quantities often within reach of experiments
in preparation. Possibilities of important contraints to models !

11. MOTIVATIONS FOR A NEW EXPERIMENT NOW
LARGE CONSENSUS ON THE DESIRABILITY OF A NEW
MEASUREMENT WITH IMPROVED SENSITIVITY
IT CAN BE DONE, MAINLY WITH EXISTING TECHNIQUES
AND SOME VITAL R&D (TO BE MADE OVER A DEFINITE PERIOD
OF TIME)
IF THE PROMISED SENSITIVITY IS REACHED, THE EXPERIMENT
IS GOING TO BE IMPORTANT EVEN IF IT DOES NOT SEE
THE EXPECTED EFFECT

12. Previous m+  e+ g Experiments
Lab.
Year
Upper limit
Experiment or Auth.
PSI
1977
< 1.0  10-9
A. Van der Schaaf et al.
TRIUMF
< 3.6  10-9
P. Depommier et al.
LANL
1979
< 1.7  10-10
W.W. Kinnison et al.
1986
< 4.9  10-11
Crystal Box
1999
< 1.2  10-11
MEGA
~2007
~ 10-13
MEG
Comparison with other
LFV searches:
Two orders of magnitude improvement
is required:
tough experimental challenge!

13. background signal SIGNAL AND BACKGROUND   e g accidental   e n n
  e g n n
ee  g g
eZ  eZ g
correlated
  e g n n
e+ + g
e+ + g n
e+ + n
qeg = 180°
Ee = Eg = 52.8 MeV
Te = Tg g

14. DETECTION METHOD qeg = 180° e+ + g signal selection with + at rest
Stopped beam of >107 /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
signal selection with + at rest
e+ + g
Ee = Eg = 52.8 MeV
qeg = 180°

15. REQUIRED PERFORMANCES
The sensitivity is limited by the accidental background
The  310-14
allows BR (meg)  but one 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
2007
0.8 4
0.15 19
2.5 x 107
1 x 10-13

16. THE MEG COLLABORATION
INFN & Genova University S. Dussoni, F. Gatti, P. Ottonello, D. Pergolesi, R. Valle
INFN & Lecce University S. Spagnolo, C. Chiri, P. Creti, G. Palama’, M. Panareo
INFN & Pavia University A.de Bari, P. Cattaneo, G. Cecchet, G. Nardo’, M. Rossella
INFN & Pisa University A. Baldini, C. Bemporad, F.Cei, M.Grassi, F. Morsani, D. Nicolo’, R. Pazzi, F. Raffaelli, F. Sergiampietri, G. Signorelli
INFN Roma I D. Zanello
ICEPP, University of Tokyo T. Mashimo, S. Mihara, T. Mitsuhashi, T. Mori, H. Nishiguchi, W. Ootani, K. Ozone, T. Saeki, R. Sawada, S. Yamashita
KEK, Tsukuba T. Haruyama, A. Maki, Y. Makida, A. Yamamoto, K. Yoshimura
Osaka University Y. Kuno
Waseda University T. Doke, J. Kikuchi, H. Okada, S. Suzuki, K. Terasawa, M. Yamashita, T. Yoshimura
Inserire i nomi sotto forma di testo e il numero di fisici equivalenti
PSI, Villigen J. Egger, P. Kettle, H. Molte, S. Ritt
Budker Institute, Novosibirsk L.M. Barkov, A.A. Grebenuk, D.G. Grigoriev, B, Khazin, N.M. Ryskulov

17. DETECTOR CONSTRUCTION
Switzerland
Drift Chambers
Beam Line
DAQ
Russia
LXe Tests
Purification
Italy
e+ counter (Pv+Ge)
Trigger (Pisa)
LXe Calorimeter(Pisa)
Splitters (Lecce)
Japan
LXe Calorimeter, Magnetic spectrometer

18.  / e separation BEAM TESTS GO ON ! SEPARATOR SOLENOID
sV  6.5mm, sH  5.3mm
primary
proton beam
1.8 mA of 590 MeV/c protons
28 MeV/c muons from  stop at rest
BEAM TESTS GO ON !
SEPARATOR SOLENOID
UNDER CONSTRUCTION

19. Constant bending radius independent of emission angles
COBRA spectrometer
COnstant Bending RAdius (COBRA) spectrometer
Constant bending radius independent of emission angles
Gradient field
Uniform field
High pT positrons quickly swept out
Gradient field
Uniform field

20. Michel Spectrum, Magnetic Field Shape and Positron Rates in Drift Chambers
e+ Rate in D.C.
Michel Spectrum
Magnetic Field
Shape

21. Ready: already shipped to PSI during summer 2003
THE MAGNET (Japan)
Bc = 1.26T current = 359A
Five coils with three different diameters
Compensation coils to suppress the stray field around the LXe detector
High-strength aluminum stabilized superconductor
thin magnet
(1.46 cm Aluminum, 0.2 X0)
Ready: already shipped to PSI during summer 2003

22. POSITRON TRACKER (PSI)
17 chamber sectors aligned radially at 10°intervals
Two staggered arrays of drift cells
Chamber gas: He-C2H6 mixture
Vernier pattern to measure z-position made of 15 m kapton foils
(X,Y) ~200 mm (drift time) (Z) ~ 300 mm
(charge division
vernier strips)

23. DRIFT CHAMBERS
preliminary test on prototype and no magnetic field gave:
FULL SCALE TEST IN DECEMBER 2003
Improved vernier strips structure (more uniform resolution)
Summary of Drift Chamber simulation
FWHM

24. Positron Timing Counter (Italy)
BC404
Two crossed layers of scintillator (0.5, 2.0 cm thick).
Hamamatsu R6504S PMT in 3 kG stray field.
Outer: timing measurement Inner: additional trigger information.
Goal time~ 40 psec (100 ps FWHM)

25.  TIMING COUNTER R&D CORTES: cosmic ray test facility.
Microstrip Chambers. 
Scintillator bar (5cm x 1cm x 100cm long)
Telescope of 8 x MSGC
Measured resolutions
time~60psec independent of impact point position
time improves as ~1/√Npe  2 cm thick

26. LIQUID XENON CALORIMETER (Italy + Japan)
800 l of Liquid Xe
800 PMT immersed in LXe
Only scintillation UV light
High light emission
Unsegmented volume
Liq. Xe
H.V.
Vacuum
for thermal insulation
Al Honeycomb
window
PMT
Refrigerator
Cooling pipe
Signals
filler
Plastic
1.5m
Experimental
verification

27. LXe CALORIMETER PERFORMANCE
Energy resolution strongly depends on optical properties of LXe
Complete MC simulations
At abs the resolution is dominated by photostatistics FWHM(E)/E  2.5% (including edge effects)
At abs  det limits from shower fluctuations + detector response  need of reconstruction algorithms
FWHM(E)/E  4%
FWHM(E)/E (%)

28. LXe CALORIMETER PROTOTYPE (the largest in the world)
The Large Prototype (LP)
40 x 40 x 50 cm3
228 PMTs, 100 litres LXe
Purpose
Test cryogenic operation on a long term and on a large volume
Measure the LXe properties
Check the reconstruction methods
Measure the Energy, Position and Timing resolutions
Use of :
Cosmic rays
-sources
e+ (60 MeV) in Japan
Back-Compton facility TERAS
50 MeV  from ° at PSI presently going on

29. HAMAMATSU PMTs
Q.E. improved to 15 %

30. THE LARGE PROTOTYPE
-sources
LEDs

31. STUDY OF LXe OPTICAL PROPERTIES
First tests showed that the number of scintillation photons was MUCH LESS than expected
It improved with Xe cleaning: Oxysorb + gas getter + re-circulation (took time)
There was a strong absorption due to contaminants (mainly H2O)
March 2002
Present...
labs> 1m

32. SIMULATION OF EFFECTS OF O2 AND H2O
CONTAMINATIONS IN LIQUID XENON

33. Timing resolution test
t = (z2 + sc2)1/2 = ( )1/2 ps = 100 ps (FWHM)
z Time-jitter due to photon interaction point
sc Scintillation time and photon statistics
our goal
Measurement of sc2 with 60 MeV electron beam
weighted average of the PMT TDCs time-walk corrected
sc vs ph.el.
extrapolation at 52.8 Mev is ok
new PMT with good QE
5 15%
52.8 MeV peak 5%
10%
15%QE

34.  - (essentially) at rest captured on protons:
ON-GOING TEST AT PSI
 - (essentially) at rest captured on protons:
 - p  0 n  - p  n 
0   
Photon spectrum
54.9
82.9
129 MeV
selection of approx. back-to-back photons
by collimators

35. 1999 measurements (R&D) with a NaI+CsI
8%FWHM
D=100 cm
10 x 10 window
9.5 hours
60 cm (NaI) 75 cm (CsI)
11 x 13 window

37. November 2003
for target ZmH
f%(CH2)=1.2

38. R&D IN XENON CALORIMETRY
Many projects, but few existing “large size” detectors
The reaching of the resolution goals, i.e.: FWHM(E)/E  4%
at  50 MeV depends on quantities still poorly known :
refractive index, attenuation length, absorption length at 178 nm
real photon
desappearance
Difficult measurements. Some data on dif are available, not always
in mutual agreement.
Gain extra information from rich data in gas and in the visible region

39. FIRST EXPERIMENTAL LOWER LIMIT ON ABSORPTION LENGTH

40. MEASUREMENT OF NEUTRON BACKGROUND thermal and non-thermal neutrons

41. Cryostat (PMT test facility: Pisa)

42. CRYOSTAT (Italy)

43. TRIGGER ELECTRONICS 2 VME 6U 1 VME 9U It uses quantities like:
 energy
Positron-  coincidence in time and direction
Built on a FADC-FPGA architecture
(field programmable gate array)
More complex algorithms implementable
1 board
2 VME 6U
1 VME 9U
Type2
LXe inner face
(312 PMT)
. . .
20 boards
20 x 48
Type1 16 3
2 boards
10 boards
10 x 48
LXe lateral faces
(488 PMT: 4 to 1 fan-in)
12 boards
12 x 48
Timing counters
(160 PMT)
2 x 48
4 x 48
Beam rate s-1
Fast LXe energy sum > 45MeV 2103 s-1
 interaction point (PMT of max charge)
e+ hit point in timing counter
time correlation  – e s-1
angular correlation  – e s-1
prototype board under test “on beam”

44. READOUT ELECTRONICS (PSI)
Waveform digitizing for all channels
Custom domino sampling chip designed at PSI
2.5 GHz sampling 40 ps timing resolution
Sampling depth 1024 bins
Readout similar to trigger
prototypes under test

45. SUMMARY FOR THE SENSITIVITY OF MEG
Cuts at 1,4FWHM
Detector parameters
Signal
 410-14
Single Event Sensitivity
 2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

46. SUMMARY AND TIME SCALE
This experiment may provide a clean indication of New Physics
Measurements and detector simulation make us confident that we can reach the SES of 4 x for e (BR 10-13)
Final prototypes are under test now
Large Prototype for energy, position and timing resolutions on ’s
Full scale Drift Chamber
-Transport and degrader-target
Tentative time profile
Revised
document
now
LoI
Proposal
Planning
R & D
Assembly
Data Taking
(<LHC)
More details at

47. TOTAL COST 6.7 (M€) Xe Calorimeter Drift chambers Timing counter
S. Solenoid
Transport Magnet HV
Trigger
Readout & DAQ
Xe 0.9
PMT 1.7
Vessel 0.4
Storage/ 0.4
purif./vacuum
0.14
0.7
1.3
0.12
0.45
0.43
6.7 (M€)

48. PHYSICAL PROPERTIES OF LIQUID RARE GASES
If impurities are not present the absorption is neglegible
The light is attenuated according to:
Scintillation mechanism:
VUV Photons
Exited excimer formation
One must determine
the attenuation length and
Transparent to its own
scintillation light
the diffusion length