1 lepton-flavour violation and neutrino oscillations carlo bemporad venezia 5/12/2003 the meg...
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LEPTON-FLAVOUR VIOLATIONAND
NEUTRINO OSCILLATIONS
http://meg.pi.infn.it
Carlo BemporadVenezia 5/12/2003
The MEG Experiment at PSI
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e
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 atomMuon-decay into three electronsMuonium-Antimuonium conversion
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HISTORY neutrino hypothesis for -decay Pauli (1930)weak interaction theory Fermi (1934)proposed method for detection Pontecorvo (1946)
ediscovery Reines and Cowan (1956)
DOES A e EXISTS ?
if equal, THEORY: ( e TOT branching ratio 10-4
Feinberg (1958), Gell-Mann and Feynman (1958)
EXPERIMENTS:no gammas Hincks and Pontecorvo (1947)B< 2 10-6 90% C.L. Berley, Lee, Bardon (1959)B< 1.9 10-7 90 C.L. Frankel et al. (1962)B< 6 10-8 90 C.L. Bartlett, Devons, Sachs (1962) ………………………………(1999) MEGA B< 1.2 10-11
Experiment by Danby at al. directly proves e (1962)
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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
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LEPTON FLAVOUR VIOLATION IS NOW AN ESTABLISHED FACT !
Atmospheric, accelerator, solar, reactor neutrino oscillationsFirst 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 advancesone probably needs new facilities
Superbeams, Large-Mass Exps., Neutrino Factories…..
While waiting for themLOOK AT SIMPLE PROCESSES IN WHICH
THE “NEW PHYSICS” CAN MANIFEST ITSELF
(Constraints to Theory even if the e decay is not seen !)
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SUGRA indications
• SUSY SU(5) predictions
BR (e) 10-14 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
LFV induced by finite slepton mixing through radiative corrections
Our goal
Experimental limit
combined LEP results favour tan>10
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Combined LEP experiments: SUGRA MSSM
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SO10
Kuno, Okada Rev.Mod.Phys. 73, 151 (2001)
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Our goal
Experimental limit
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)
tan()=30
tan()=1
After SNO After Kamland
-5410R in the Standard Model !
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Vast Recent Literature on SUSY and Connection betweenNeutrino-oscillations, LFV rare decays, EDM, g-2.
Rather technical papersConstraints from new experimental informationEven the full knowledge of neutrino masses and mixing anglesis able to determine the seesaw parameters like: the neutrinoYukawa coupling h and the heavy right-handed neutrino Maiorana mass MR (and therefore e…).Complementary informations. (Masiero, Vempati hep-ph/0209303) Predictions for measurable quantities often within reach of experimentsin preparation. Possibilities of important contraints to models !
Examples:Hisano, Nomura, PRD 59, 116005 (1999) Casas, Ibarra, hep-ph0103065Lavignac, Masina, Savoy, hep-ph/0106245 Babu, Pati, hep-ph/0207289Raidal, Strumia, PLB 553, 72 (2003) Barr, hep-ph/0307372Blažek, King, NPB 662, 359 (2003) Masiero, Vempati, hep-ph/0209303Petcov, Profumo, Takanishi, Yaguna, NPB9187 in press
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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
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Previous + e+ Experiments
Lab. Year Upper limit Experiment or Auth.
PSI 1977 < 1.0 10-9 A. Van der Schaaf et al.
TRIUMF 1977 < 3.6 10-9 P. Depommier et al.
LANL 1979 < 1.7 10-10 W.W. Kinnison et al.
LANL 1986 < 4.9 10-11 Crystal Box
LANL 1999 < 1.2 10-11 MEGA
PSI ~2007 ~ 10-13 MEG
Comparison with other LFV searches:
Two orders of magnitude improvement is required:
tough experimental challenge!
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SIGNAL AND BACKGROUND
e+ +
e = 180°
Ee = E = 52.8 MeV
Te = T
signal e
background
correlated
e
e+ +
accidental
e e
ee
eZ eZ
e+ +
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DETECTION METHOD
1m
e+
Liq. Xe Scintilla tionDetector
Drift Chamber
Liq. Xe Scintilla tionDetector
e+
Tim ing Counter
Stopping TargetThin S uperconducting Coil
M uon Beam
Drift Chamber
signal selection with + at rest
e+ + Ee = E = 52.8 MeV
e = 180°
• Stopped beam of >107 /sec
in a 150 m 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
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REQUIRED PERFORMANCES
Exp./Lab Year Ee/Ee
(%)
E/E
(%)
te (ns)
e
(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 1977 10 8.7 6.7 - 2 x 105 100 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 8 8 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 107 100 1 x 10-13
The sensitivity is limited by the accidental background
The 310-14
allows BR (e) 10-13 but one needs
eγ2
eγ2
γeμacc ΔΔΔΔ tθEERBR
FWHM
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INFN & Pisa University A. Baldini, C. Bemporad, F.Cei, M.Grassi, F. Morsani, D. Nicolo’, R. Pazzi, F. Raffaelli, F. Sergiampietri, G. Signorelli
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
Budker Institute, Novosibirsk L.M. Barkov, A.A. Grebenuk, D.G. Grigoriev, B, Khazin, N.M. Ryskulov
PSI, Villigen J. Egger, P. Kettle, H. Molte, S. Ritt
THE MEG COLLABORATION
INFN & Pavia University A.de Bari, P. Cattaneo, G. Cecchet, G. Nardo’, M. Rossella
INFN & Genova University S. Dussoni, F. Gatti, P. Ottonello, D. Pergolesi, R. Valle
INFN Roma I D. Zanello
INFN & Lecce University S. Spagnolo, C. Chiri, P. Creti, G. Palama’, M. Panareo
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DETECTOR CONSTRUCTION
SwitzerlandSwitzerlandDrift ChambersBeam LineDAQ
JapanJapanLXe Calorimeter, Magnetic spectrometer
RussiaRussiaLXe TestsPurification
ItalyItalye+ counter (Pv+Ge)Trigger (Pisa)LXe Calorimeter(Pisa)Splitters (Lecce)
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• 1.8 mA of 590 MeV/c protons
• 28 MeV/c muons from stop at rest
primaryproton beam
/ e separation
V 6.5mm, H 5.3mm
BEAM TESTS GO ON !SEPARATOR SOLENOID UNDER CONSTRUCTION
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COBRA spectrometer
Gradient field Uniform field
Gradient field Uniform field
COnstant Bending RAdius (COBRA) spectrometer
Constant bending radius independent of emission angles
• High pT positrons quickly swept out
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Michel Spectrum, Magnetic Field Shape and Positron Rates in Drift Chambers
Michel Spectrum
Magnetic Field Shape
e+ Rate in D.C.
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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
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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 m (drift time) (Z) ~ 300 m (charge divisionvernier strips)
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DRIFT CHAMBERS
• FULL SCALE TEST IN DECEMBER 2003
• Improved vernier strips structure (more uniform resolution)
• Summary of Drift Chamber simulation
mmx
mrad
PP
orig
e
ee
5.21.2
129
%9.07.0/
FW
HM
m
m
Z
R
7425
1093
preliminary test on prototype and no magnetic field gave:
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Positron Timing Counter (Italy)
• 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)
BC404
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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
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• 800 l of Liquid Xe
• 800 PMT immersed in LXe
• Only scintillation UV light
• High light emission
• Unsegmented volume
LIQUID XENON CALORIMETER (Italy + Japan)
Liq. Xe
H.V.
Vacuum
for thermal insulation
Al Honeycombwindow
PMT
Refrigerator
Cooling pipe
Signals
fillerPlastic
1.5m
Experimentalverification
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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%
FWH
M(E
)/E (
%)
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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-sourcese+ (60 MeV) in JapanBack-Compton facility TERAS50 MeV from ° at PSI presently
going on
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HAMAMATSU PMTs
Q.E. improved to 15 %
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LEDs
-sources
THE LARGE PROTOTYPE
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STUDY OF LXe OPTICAL PROPERTIES
Present... March 2002
•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)
absabs> 1m> 1m
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SIMULATION OF EFFECTS OF O2 AND H2O CONTAMINATIONS IN LIQUID XENON
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Timing resolution test
t = (z2 + sc
2)1/2 = (802 + 602)1/2 ps = 100 ps (FWHM)
z Time-jitter due to photon interaction point
sc Scintillation time and photon statistics
Measurement of sc2 with 60 MeV electron
beam
our goal
• 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%
5%10%
15%QE
52.8 MeV peak
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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 photonsby collimators
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1999 measurements (R&D) with a NaI+CsI
•D=100 cm
•10 x 10 window
•9.5 hours
•60 cm (NaI) 75 cm (CsI)
•11 x 13 window
8%FWHM
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November 2003
for target ZmH f%(CH2)=1.2
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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
R&D IN XENON CALORIMETRY
Many projects, but few existing “large size” detectors
real photondesappearance
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
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FIRST EXPERIMENTAL LOWER LIMIT ON ABSORPTION LENGTH
1 m
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MEASUREMENT OF NEUTRON BACKGROUND thermal and non-thermal neutrons
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Cryostat (PMT test facility: Pisa)
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CRYOSTAT (Italy)
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TRIGGER ELECTRONICS
Beam rate 108 s-1
Fast LXe energy sum > 45MeV 2103
s-1
interaction point (PMT of max charge)
e+ hit point in timing counter time correlation – e+ 200 s-1
angular correlation – e+ 20 s-1
•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
prototype board under test “on beam”
1 board
2 VME 6U
1 VME 9U
Type2
Type2
LXe inner face
(312 PMT)
. .
. 20 boards
20 x 48
Type1Type1Type1
16
3
Type2
2 boards
. . .
10 boards
10 x 48
Type1Type1Type1
16
3
LXe lateral faces
(488 PMT: 4 to 1 fan-in)
Type2
1 board
. . .
12 boards
12 x 48
Type1Type1
Type1
16
3
Timing counters
(160 PMT) Type2Type2
2 boards2 x 48
4 x 48
2 x 48
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READOUT ELECTRONICS (PSI)
• Waveform digitizing for all channels
• Custom domino sampling chip designed at PSI
• 2.5 GHz sampling speed @ 40 ps timing resolution
• Sampling depth 1024 bins
• Readout similar to trigger
prototypes under test
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SUMMARY FOR THE SENSITIVITY OF MEG
0.6ε 0.70.9ε 0.9ε γ3
sele
0.09 4π Ω
sμ100.3R s102.6T 8
μ7
Cuts at 1,4FWHM
Detector parameters
seleμsig
4
RTBRNSignal
seleμ
4RT
1SES 410-
14
Single Event Sensitivity
corrBReγ
2eγ
2γeμacc ΔΔΔΔ tθEERBR 210-
14
310-
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Backgrounds
Upper Limit at 90% CL BR (e) 110-13
Discovery 4 events (P = 210-3) correspond BR = 210-13
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http://meg.psi.chhttp://meg.pi.infn.it
http://meg.icepp.s.u-tokyo.ac.jp
http://meg.psi.chhttp://meg.pi.infn.it
http://meg.icepp.s.u-tokyo.ac.jp
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 10-14 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
More details at
1998 1999 2000 2001 2002 2003 2004 2005 2006 2007
Planning R & D Assembly Data Taking
nownowLoILoI ProposalProposalRevisedReviseddocumentdocument
(<LHC)
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TOTAL COST
Xe CalorimeterXe Calorimeter
Drift chambersDrift chambers
Timing counterTiming counter
S. SolenoidS. Solenoid
Transport MagnetTransport Magnet
HVHV
TriggerTrigger
Readout & DAQReadout & DAQ
XeXe 0.90.9
PMTPMT 1.71.7
VesselVessel 0.40.4
Storage/Storage/ 0.40.4
purif./vacuumpurif./vacuum
0.140.14
0.70.7
1.31.3
0.140.14
0.120.12
0.450.45
0.430.43
6.7 (M€)6.7 (M€)
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PHYSICAL PROPERTIES OF LIQUID RARE GASES
Scintillation mechanism:
VUV Photons
Transparent to its own scintillation light
• If impurities are not present the absorption is neglegible
• The light is attenuated according to:
One must determinethe attenuation length and
the diffusion length
Exited excimer formation