Dec. 8th, 2000 NOON 2000 1

A new e experiment at PSI

For the MUEGAMMA collaborationStefan Ritt

(Paul Scherrer Institute, Switzerland)

• Introduction

• Experimental Technique

• Current status

Dec. 8th, 2000 NOON 2000 2

Physics Motivation• SUSY theories generically predict LFV• LFV forbidden by Standard Model• Processes like + e+ are not “contaminated” by SM

processes and therefore very clean• Discovered oscillations are expected to enhance LFV

rate• The search for + e+ is therefore a promising field to

find physics beyond the SM

Dec. 8th, 2000 NOON 2000 3

Prediction from SUSY SU(5)

This experiment

Current experimental bound 2)

ft(M)=2.4 >0 Ml=50GeV 1)

1) J. Hisano et al., Phys. Lett. B391 (1997) 3412) MEGA collaboration, hep-ex/9905013

Dec. 8th, 2000 NOON 2000 4

10

J ust so

(GeV)M R2

141312101010

bound

Experimental

-1-2-3 11010

MSW small angle

MSW large anglesmall mass

J ust so

MSW large angle

sin 22

m

2(e

V )2

e

)

Br(

10

10

10

10

10

10

10

10

-3

-4

-5

-6

-7

-8

-9

-10

10

-11

10

10

10

10

10

10

-10

-11

-12

-13

-14

-15

MSW

larg

e an

gle

MSW

small a

ngle

~ larg

e an

gle sm

all m

ass

Connection with oscillations1)

1) J. Hisano and D. Nomura, Phys. Rev. D59 (1999) 116005

2) MEGA collaboration, hep-ex/9905013

2)

This experiment

Dec. 8th, 2000 NOON 2000 5

Previous + e+ Experiments

Place Year Upper limit Author

SIN (PSI), Switzerland 1977 < 1.0 10-9 A. Van der Schaaf et al.

TRIUMF, Canada 1977 < 3.6 10-9 P. Depommier et al.

LANL, USA 1979< 1.7 10-10

W.W. Kinnison et al.

LANL, USA 1986 < 4.9 10-11 R.D. Bolton et al.

LANL, USA 1999 < 1.2 10-11 MEGA Collab., M.L. Brooks et al.

• New experiment: 10-14 at PSI• Letter of Intend 1998• Proposal 1999, approved May 1999

• New experiment: 10-14 at PSI• Letter of Intend 1998• Proposal 1999, approved May 1999

Dec. 8th, 2000 NOON 2000 6

MEG Collaboration

Institute Country Main Resp. Head Scientists Students

ICEPP, Univ. of Tokyo Japan LXe Calorimeter T. Mori 12 2

Waseda University Japan Cryogenics T. Doke 5 2

INFN, Pisa Italye+ counter, trigger, M.C.

C. Bemporad 4 3

IPNS, KEK, Tsukuba JapanSupercoducting Solenoid

A. Maki 5 -

PSI SwitzerlandDrift Chamber, Beamline, DAQ

S. Ritt 4 -

BINP, Novosibirsk RussiaLXe Tests and Purification

B. Khazin 4 -

Nagoya University Japan Cryogenics K. Masuda 1 -

35 7

Dec. 8th, 2000 NOON 2000 7

Experimental 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

• Stopped beam of 108 s-1, 100% duty factor

• Liquid Xe calorimeter

for detection

• Solenoidal magnetic spectrometer with gradient field

• Radial drift chambers for e+ momentum determination

• Timing counter for e+

• Stopped beam of 108 s-1, 100% duty factor

• Liquid Xe calorimeter

for detection

• Solenoidal magnetic spectrometer with gradient field

• Radial drift chambers for e+ momentum determination

• Timing counter for e+

Ee = 52.8 MeV

Kinematics e= 180°

Eg = 52.8 MeV

e

Dec. 8th, 2000 NOON 2000 8

Signal and Background• + e+ signal very clear

– E = Ee+ = 52.8 MeV

– e+ = 180°

– e+ and in time

• Background– Radiative + decays– Accidental overlap

• Detector Requirements– Excellent energy resolution– Excellent timing resolution– Good angular resolution

e

e

e

e

e

e

e

Dec. 8th, 2000 NOON 2000 9

e Signature

eEe,E = 52.8MeV

eEe,E < 52.8MeV

0.9

0.92

0.94

0.96

0.98

1

1.02

0.9 0.92 0.94 0.96 0.98 1 1.02X

Y

10 14 Decays in Acceptance

X = Ee/52.8MeV

Y =

E/

52.8

MeV

Dec. 8th, 2000 NOON 2000 10

Sensitivity and Background Rate

BR(e) = (N • T • /4 • e • • sel )-1 = 0.94 10-14

N 1108

T 2.2 107 s (~50 weeks)

/4 0.09

e 0.95

0.7

sel 0.8

FWHM

Ee 0.7%

E 1.4%

e 12 mrad

te 150 ps

Prompt Background Bpr 10-17

Accidental Background Bacc Ee • te • (E)2 • (e)2 5 10-15

Dec. 8th, 2000 NOON 2000 11

Paul Scherrer Institute

ExperimentalHall

Dec. 8th, 2000 NOON 2000 12

Experimental Hall

Dec. 8th, 2000 NOON 2000 13

Sindrum II @ PSI

-Ti e-Ti :

Oct. 2000 (50d) beam time:

90% C.L. limit: 6.1• 10-13

Bue=4 •10-12Bue=4 •10-12

Dec. 8th, 2000 NOON 2000 14

E5 Beam Line

e

U-versionE52

Z-versionE51

AST

First Degrader

Beam transport

ASC

Detector

solenoid

• 108 /s on 55 mm2

• Neutron background measured in 1998• Beam test planned in Spring 2001

• 108 /s on 55 mm2

• Neutron background measured in 1998• Beam test planned in Spring 2001

Dec. 8th, 2000 NOON 2000 15

Detector

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

Dec. 8th, 2000 NOON 2000 16

LXe Calorimeter

• ~800l liquid Xe (3t)

• ~800 PMTs immersed in LXe

• Only scintillation light detected

• Fast response (45 ns decay time)

• High light output (70% of NaI(Tl))1)

• High uniformity compared with segmented calorimeters

• High channel occupancy will be accommodated by special trigger scheme

• ~800l liquid Xe (3t)

• ~800 PMTs immersed in LXe

• Only scintillation light detected

• Fast response (45 ns decay time)

• High light output (70% of NaI(Tl))1)

• High uniformity compared with segmented calorimeters

• High channel occupancy will be accommodated by special trigger scheme

Liq. Xe

H.V.

Vacuum

for thermal insulation

Al Honeycombwindow

PMT

Refrigerator

Cooling pipe

Signals

fillerPlastic

1.5m

1) T. Doke and K. Masuda, NIM A 420 (1999) 62

Dec. 8th, 2000 NOON 2000 17

Response

3 cm

Liq. Xe

Liq. Xe

14 cm

(a)

(b)

05 10 15

2025

3035

0

10

20

30

40

50

0

2000

4000

6000

8000

10000

05

1015 20 25

3035

0

10

20

30

40

50

0

200

400

600

800

1000

1200

1400

1600

1800

52.8 MeV

52.8 MeV

• Signal is distributed over many PMTs in most cases

• Weighted mean of PMTs on the front face x ~ 4mm FWHM

• Broadness of distribution z ~ 16mm FWHM

• Timing resolution t ~ 100ps FWHM

• Energy resolution ~ 1.4% FWHMdepends on light attenuation in LXe

• Signal is distributed over many PMTs in most cases

• Weighted mean of PMTs on the front face x ~ 4mm FWHM

• Broadness of distribution z ~ 16mm FWHM

• Timing resolution t ~ 100ps FWHM

• Energy resolution ~ 1.4% FWHMdepends on light attenuation in LXe

x

z

Dec. 8th, 2000 NOON 2000 18

Calorimeter Prototypes

• 32 PMTs, 2.3 l LXe• Tested with radioactive sources

51Cr, 137Cs, 54Mn, 88Y• Extrapolated resolutions at 52.8 MeV

in agreement with quoted numbers

“Small” “Large”

• 264 PMTs,150 l LXe

• Assembly finished next January

• Measure resolutions with 40 MeV photon beam at ETL, Tsukuba, Japan

Dec. 8th, 2000 NOON 2000 19

Positron SpectrometerHomogeneous Field

Gradient Field(COnstant-Bending-RAdius)

e+ from +e+e+ from +e+

Ultra-Thin (~3g/cm2)superconducting solenoidwith 1.2 T field

Ultra-Thin (~3g/cm2)superconducting solenoidwith 1.2 T field

Dec. 8th, 2000 NOON 2000 20

Drift Chamber

• 16 radial chambers with 20 wires each• Staggered cells measure both position and time• He – C2H6 gas to reduce multiple scattering• Vernier pattern to determine z coordinate

• 16 radial chambers with 20 wires each• Staggered cells measure both position and time• He – C2H6 gas to reduce multiple scattering• Vernier pattern to determine z coordinate

Dec. 8th, 2000 NOON 2000 21

Prototype Test at PSI

• 0, 0.6, 0.8, 1T field

• 3 tilting angles

• Data analysis finished soon

• 0, 0.6, 0.8, 1T field

• 3 tilting angles

• Data analysis finished soon

Dec. 8th, 2000 NOON 2000 22

Positron timing counter

z

(t )z L

(t )R

L(t )

Rz(t )

e+

e+

e+

Impact Point

1m

• Aimed resolution ~100ps FWHM

• Beam tests at KEK in July 1999

• Taken over by Pisa group

• Scintillators ordered• Beam tests next

spring

• Aimed resolution ~100ps FWHM

• Beam tests at KEK in July 1999

• Taken over by Pisa group

• Scintillators ordered• Beam tests next

spring

e+

Timing Counter

Stopping TargetThin Superconducting Coil

Muon Beam

Drift Chamber

Dec. 8th, 2000 NOON 2000 23

Trigger Requirements

Beam rate 108 s-1

Fast LXe energy sum > 45MeV2103 s-1

interaction point e+ hit point in timing counter time correlation – e+ 200 s-

1

angular corrlation – e+ 20 s-1

Beam rate 108 s-1

Fast LXe energy sum > 45MeV2103 s-1

interaction point e+ hit point in timing counter time correlation – e+ 200 s-

1

angular corrlation – e+ 20 s-1

Ee = 52.8 MeV

Kinematics e= 180°

Eg = 52.8 MeV

e

M.C.

e+

Dec. 8th, 2000 NOON 2000 24

Trigger Implementation

FADC

100MHz 8-bit

FPGAFADC

FADC

FADC

SRAM

Trigger

FADC

FPGAFADC

FADC

FADC

SRAM

BS

BS

BS

BS

Max

Max

Max

.

.

.

T[ns] 0 50 60 70..150 160 170

>45MeV

e+

AND

10 stages = 1024 chn

…800 channels

-

BaselineSubtraction

. . .

Dec. 8th, 2000 NOON 2000 25

Waveform Digitizing

• Waveform Digitizing for all channels• Custom domino sampling chip (DSC) designed at PSI• Costs per DSC ~1US$• 2.5 GHz sampling speed 40ps timing resolution• Sampling depth 1024 bins 400ns (100ns+300ns)• Readout electronics similar to trigger• Drift chamber signals go directly to FADC (100MHz)

• Waveform Digitizing for all channels• Custom domino sampling chip (DSC) designed at PSI• Costs per DSC ~1US$• 2.5 GHz sampling speed 40ps timing resolution• Sampling depth 1024 bins 400ns (100ns+300ns)• Readout electronics similar to trigger• Drift chamber signals go directly to FADC (100MHz)

FPGAFADC SRAM. . .

Analog Waveform Sampling Chip (DSC)

2.5GHz

40MHz, 10 bit

VME

Previous Version 1.2 GHz

C. Brönnimann et al., NIM A420 (1999) 264

Dec. 8th, 2000 NOON 2000 26

Time Table

1997 1998 1999 2000 2001 2002 2003 2004 2005

Planning R & D Assembly Data Taking

now

Conclusions• Preparations are going well in all areas of the experiment• Innovative technologies developed useful for other experiments• Next major milestone: Large prototype test in Tsukuba spring 2001• Increasing support from PSI and Pisa• New collaborators are welcome

• Preparations are going well in all areas of the experiment• Innovative technologies developed useful for other experiments• Next major milestone: Large prototype test in Tsukuba spring 2001• Increasing support from PSI and Pisa• New collaborators are welcome

http://meg.icepp.s.u-tokyo.ac.jphttp://meg.pi.infn.ithttp://meg.psi.ch

http://meg.icepp.s.u-tokyo.ac.jphttp://meg.pi.infn.ithttp://meg.psi.ch