MEG

1

e search at PSI: 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 slepton mixing

Our goal

Experimental limit

combined LEP results favour tan>10 -5410R in the Standard Model !!

MEG

2

Experimental method

1m

e+

Liq. Xe Scin tilla tionDetector

Drift Cham ber

Liq. Xe Scin tilla tionDetector

e+

Tim ing Counter

Stopping TargetThin S uperconducting Coil

M uon Beam

Drift Cham ber

Easy signal selection with + at rest

e+ + Ee = E = 52.8 MeV

e = 180°Detector outline

• Stopped beam of 3 107 /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

MEG

3

INFN & Pisa University A. Baldini, C. Bemporad, F.Cei, M.Grassi, F. Morsani, D. Nicolo’, A. Papa, R. Pazzi, F. Raffaelli, F. Sergiampietri, G. Signorelli

ICEPP, University of Tokyo Y. Hisamatsu, T. Iwamoto, T. Mashimo, S. Mihara, T. Mori, H. Natori, H. Nishiguchi, W. Ootani, K. Ozone, R. Sawada, Y. Uchiyama, S. Yamada, S. Yamashita

KEK, Tsukuba T. Haruyama, A. Maki, Y. Makida, A. Yamamoto, K. Yoshimura

Waseda University T. Doke, J. Kikuchi, H. Okada, S. Suzuki, K. Terasawa, M. Yamaguchi

Budker Institute, Novosibirsk L.M. Barkov, A.A. Grebenuk, D.G. Grigoriev, B, Khazin, N.M. Ryskulov

PSI, Villigen J. Egger, P. Kettle, M. Hildebrandt, S. Ritt, M. Schneebeli

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, C. Gatto,G. Marsella, G. Palama’, M. Panareo, G. Tassielli

The MEG collaboration

MEG

4

Detector Construction

SwitzerlandSwitzerlandDrift ChambersBeam LineDAQ

JapanJapanLXe Calorimeter, Spectrometer’s magnet

RussiaRussiaLXe TestsPurification

ItalyItalye+ counter (Pv+Ge)Trigger (Pisa)LXe Calorimeter(Pisa)Splitters (Lecce)

MEG

5

COnstant Bending RAdius (COBRA) spectrometer

Gradient field Uniform field

• Constant bending radius independent of emission angles

• High pT positrons quickly swept out

Gradient field Uniform field

• 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: at PSI !!

MEG

6

Positron Tracker (PSI)

• 17 chamber sectors aligned radially with 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)

goalsOK To be proved in

mag.field

MEG

7

Positron Timing Counter (Pavia + Genova + Roma )

• One (outer) layer of scintillator read by PMTs : timing•One inner layer of scintillating fibers read by APDs: trigger (the long. Position

is needed for a fast estimate of the positron direction)•Goal time~ 40 psec (100 ps FWHM) reached in tests

BC404

5 x 5 mm2

MEG

8

• 800 l of Liquid Xe

• ~800 PMT immersed in LXe

• Only scintillation light

• High luminosity

• Unsegmented volume

Liquid Xe calorimeter (Pisa + Tokyo + KEK)

FWHM =FWHM =4.8 ± 0.3%4.8 ± 0.3%

55 MeV

R<1.5cm

40 MeV and 1 mm collimator

•Measured position and energy resolutions with a 100 liters prototype

• Cryostat in construction

• 150 ps FWHM timing resolution proved

MEG

9

Trigger Electronics (Pisa)

Beam rate 108

s-1

Fast LXe energy sum > 45MeV2103 s-1

g interaction point (PMT of max charge)

e+ hit point in timing counter

time correlation – e+ 200 s-1

angular correlation – e+ 20 s-1

•Uses easily quantities:

energy

•Positron- coincidence in time and direction

•Built on a FADC-FPGA architecture

•More complex algorithms implementable

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

Prototype board

tested at PSI

MEG

10

Readout electronics (PSI): Domino Ring Sampler (DRS chip)

• Analog 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

•Spike structure will be simply fixed by re-programming FPGA on the board.

2.5 GHz

Set of 1024 capacitors40 MHz 11 bit

Prototype tested with 55 MeV photons in the 100 l prototype

raw After calibrations

MEG

11

Sensitivity Summary

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-

15

Backgrounds

Upper Limit at 90% CL BR (e) 110-13

MEG

12

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

Sensitivity and time schedule

• Total measurement time: 2 years (50% duty cycle of PSI beam)

• One e event observed if BR = 4 x 10-14

• If no event observed upper BR limit at 90% CL = 10-13

Discovery: 4 events (P = 210-3) correspond to BR = 210-

13

• Final prototypes being tested• Full scale Drift Chamber

• Time profile

More details at

1998 1999 2000 2001 2002 2003 2004 2005 2006 2007

Planning R & D Assembly Data Taking

nownowLoILoI ProposalProposalRevisedReviseddocumentdocument

<LHC