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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