Upload
mari-mccall
View
26
Download
4
Tags:
Embed Size (px)
DESCRIPTION
Lepton Flavor Violation : Goals and Status of the MEG Experiment at PSI. Stefan Ritt Paul Scherrer Institute, Switzerland. Agenda. Search for m e g down to 10 -13 Motivation Experimental Method Status and Outlook. Motivation. Why should we search for m e g ?. - PowerPoint PPT Presentation
Citation preview
Lepton Flavor Violation:Goals and Status of the MEG
Experiment at PSI
Stefan RittPaul Scherrer Institute, Switzerland
26 June '07 Particle Colloquium Heidelberg 2
Agenda
Search for e down to 10-13
• Motivation
• Experimental Method
• Status and Outlook
Motivation
Why should we search for e ?
26 June '07 Particle Colloquium Heidelberg 4
The Standard Model
Fermions (Matter)
Quarks
uup
ccharm
ttop
ddown
sstrange
bbottom
Lepto
ns
eelectronneutrino
muon
neutrino
tau
neutrino
eelectron
muon
tau
Bosons
photon
Force
carrie
rs
ggluon
WW boson
ZZ boson
Higgs*
boson
*) Yet to be confirmedGeneration I II III
26 June '07 Particle Colloquium Heidelberg 5
The success of the SM
• The SM has been proven to be extremely successful since 1970’s
• Simplicity (6 quarks explain >40 mesons and baryons)
• Explains all interactions in current accelerator particle physics
• Predicted many particles (most prominent W, Z )
• Limitations of the SM
• Currently contains 19 (+10) free parameters such as particle (neutrino) masses
• Does not explain cosmological observation such as Dark Matter and Matter/Antimatter Asymmetry
CDF
Today’s goal is to look for physics beyond the standard
model
Today’s goal is to look for physics beyond the standard
model
26 June '07 Particle Colloquium Heidelberg 6
Beyond the SM
Find New PhysicsBeyond the SM
High Energy Frontier
• Produce heavy new particles directly• Heavy particles need large colliders• Complex detectors
High Precision Frontier
• Look for small deviations from SM (g-2) , CKM unitarity
• Look for forbidden decays• Requires high precision at low energy
26 June '07 Particle Colloquium Heidelberg 7
Neutron beta decay
Neutron decay via intermediate heavy W- boson
ddu
udu
pn
W -e-
e
n p+ + e - + e
~80 MeV
~5 MeV
Neutron mean life
time:
886 s
Neutron mean life
time:
886 s
decay discovery:
~1934
W- discovery:
1983
decay discovery:
~1934
W- discovery:
1983
26 June '07 Particle Colloquium Heidelberg 8
New physics in decay
Can’t we do the same in decay?
e-??
Probe physics at TeV scale with high precision decay measurement Probe physics at TeV scale with high precision decay measurement
26 June '07 Particle Colloquium Heidelberg 9
•Discovery: 1936 in cosmic radiation
•Mass: 105 MeV/c2
•Mean lifetime: 2.2 s
The MuonSeth Neddermeyer
Carl Anderson
e
-
W-e-
e
e
e
e
e ≈ 100%
0.014
< 10-11
led to Lepton Flavor Conservationas “accidental” symmetry
26 June '07 Particle Colloquium Heidelberg 10
Lepton Flavor Conservation
• Absence of processes such as e led to concept of lepton flavor conservation
• Similar to baryon number (proton decay) and lepton number conservation
• These symmetries are “accidental” because there is no general principle that imposes them – they just “happen” to be in the SM (unlike charge and energy conservation)
• The discovery of the failure of such a symmetry could shed new light on particle physics
26 June '07 Particle Colloquium Heidelberg 11
LFV and Neutrino Oscillations
Neutrino Oscillations Neutrino mass e possible even in the SM
W-
ee-
SM
604
4B 10R( )
W
em
m
LFV in the charged sector is forbidden in the Standard Model
LFV in the charged sector is forbidden in the Standard Model
mixing
26 June '07 Particle Colloquium Heidelberg 12
LFV in SUSY
• While LFV is forbidden in SM, it is possible in SUSY
W-
ee-
e-0~
~e~
SM
604
4B 10R( )
W
em
m
SUSYBR( )e
4
5 2
SUS2
Y
2100 GeV
10 tanem
mm
≈ 10-12
Current experimental limit: BR( e ) < 10-11Current experimental limit: BR( e ) < 10-11
2~~em
26 June '07 Particle Colloquium Heidelberg 13
• LFV is forbidden in the SM, but possible in SUSY (and many other extensions to the SM) though loop diagrams ( heavy virtual SUSY particles)
• If e is found, new physics beyond the SM is found
• Current exp. limit is 10-11, predictions are around 10-12 … 10-14
• First goal of MEG: 10-13
• Later maybe push to 10-14 ($$$)
• Big experimental challenge
• Solid angle * efficiency (e,) ~ 3-4 %
• 107 – 108 /s DC beam needed
• ~ 2 years measurement time
• excellent background suppression
LFV Summary
26 June '07 Particle Colloquium Heidelberg 14
History of LFV searches
• Long history dating back to 1947!
• Best present limits:
• 1.2 x 10-11 (MEGA)
• Ti → eTi < 7 x 10-13 (SINDRUM II)
• → eee < 1 x 10-12 (SINDRUM II)
• MEG Experiment aims at 10-13
• Improvements linked to advancein technology
1940 1950 1960 1970 1980 1990 2000 2010
10-1
10-2
10-3
10-4
10-5
10-6
10-7
10-6
10-9
10-10
10-11
10-12
10-13
10-14
10-15
→ e → eA → eee
MEG
SUSY SU(5)
BR( e ) = 10-13
Ti eTi = 4x10-16
BR( eee) = 6x10-16
SUSY SU(5)
BR( e ) = 10-13
Ti eTi = 4x10-16
BR( eee) = 6x10-16
cosmic
stopped
beams
stopped
26 June '07 Particle Colloquium Heidelberg 15
Current SUSY predictions
“Supersymmetric parameterspace accessible by
LHC”
“Supersymmetric parameterspace accessible by
LHC”
W. Buchmueller, DESY, priv. comm.
current limit
MEG goal
1) J. Hisano et al., Phys. Lett. B391 (1997) 3412) MEGA collaboration, hep-ex/9905013
ft(M)=2.4 >0 Ml=50GeV 1)
tan
26 June '07 Particle Colloquium Heidelberg 16
LFV link to other SUSY proc.
e-0~
~e~
2~~em
0~
~
2~~m
e-LFVe-LFV
gg
~
0~
~
2~~m
~
EDMEDM
2~~
2~~
2~~
2~~
2~~
2~~
2~~
2~~
2~~
mmm
mmm
mmm
te
e
eeee
slepton mixing matrix:
1227 10
)(sin3.1
10
eBR
cme
de
In SO(10), eEDM is related to e
In SO(10), eEDM is related to e
R. Barbieri et al., hep-ph/9501334
Experimental Method
How to detect e ?
26 June '07 Particle Colloquium Heidelberg 18
Decay topology e
e
e
180º
→ e signal very clean• Eg = Ee = 52.8 MeV• e = 180º• e and in time
52.8 MeV
52.8 MeV
10 20 30 40 50 60 E[MeV]
N
52.8 MeV
10 20 30 40 50 60 Ee[MeV]
N
52.8 MeV
26 June '07 Particle Colloquium Heidelberg 19
Michel Decay (~100%)
Three body decay: wide energy spectrum
e
e
Ee[MeV]
N 52.8 MeV
Ee[MeV]
N 52.8 MeV
TheoreticalTheoretical
Convoluted withdetector resolution
Convoluted withdetector resolution
26 June '07 Particle Colloquium Heidelberg 20
Radiative Muon Decay (1.4%)
e
e
E[MeV]
N 52.8 MeV
“Prompt” Background“Prompt” Background
26 June '07 Particle Colloquium Heidelberg 21
“Accidental” Background
e
e
180º
→ e signal very clean• Eg = Ee = 52.8 MeV• e = 180º• e and in time
e
e
e
e
Annihilationin flight
Background
Good energy resolutionGood spatial resolution
Excellent timing resolutionGood pile-up rejection
26 June '07 Particle Colloquium Heidelberg 22
Previous Experiments
Exp./Lab
Author Year Ee/Ee
%FWHM
E/E
%FWHM
te
(ns)
e
(mrad)
Inst. Stop rate (s-1)
Duty cycle (%)
Result
SIN (PSI)
A. Van der Schaaf
1977 8.7 9.3 1.4 - (4..6) x 105 100 < 1.0 10-9
TRIUMFP.
Depommier1977 10 8.7 6.7 - 2 x 105 100 < 3.6 10-9
LANLW.W.
Kinnison1979 8.8 8 1.9 37 2.4 x 105 6.4 < 1.7 10-10
Crystal Box
R.D. Bolton 1986 8 8 1.3 87 4 x 105 (6..9) < 4.9 10-11
MEGA M.L. Brooks 1999 1.2 4.5 1.6 17 2.5 x 108 (6..7) < 1.2 10-11
MEG ? ? ? ? ? ? ~ 10-13
How can we achieve a quantum step in detector technology?How can we achieve a quantum step in detector technology?
26 June '07 Particle Colloquium Heidelberg 23
How to build a good experiment?
26 June '07 Particle Colloquium Heidelberg 24
Collaboration
~70 People (40 FTEs) from five countries
26 June '07 Particle Colloquium Heidelberg 25
Paul Scherrer Institute
Swiss Light Source
Proton Accelerator
26 June '07 Particle Colloquium Heidelberg 26
PSI Proton Accelerator
26 June '07 Particle Colloquium Heidelberg 27
Generating muonsCarbon Target
590 MeV/c2 Protons1.8 mA = 1016 p+/s
+
+
+
+
108 +/s
26 June '07 Particle Colloquium Heidelberg 28
Muon Beam Structure
Muon beam structure differs for different accelerators
Pulsed muon beam, LANL
Duty cycle: Ratio of pulse width over period
DC muon beam, PSI
Duty cycle: Ratio of pulse width over period
Duty cycle: 6 % Duty cycle: 100 %
Instantaneous rate much higher in pulsed beamInstantaneous rate much higher in pulsed beam
26 June '07 Particle Colloquium Heidelberg 29
Muon Beam Line
Transport 108 +/s to stopping target inside detector with minimal background
+ from production target
x
x
x x
x x+
e+
-
+
0)(!
BvEqF
Lorentz Force vanishes for given v:Lorentz Force vanishes for given v:
Wien FilterWien Filter
26 June '07 Particle Colloquium Heidelberg 30
Results of beam line optimization
+
R ~ 1.1x108 +/s at experiment
~ 10.9 mm ~ 10.9 mm
e+
+
26 June '07 Particle Colloquium Heidelberg 31
Previous Experiments
Exp./Lab
Author Year Ee/Ee
%FWHM
E/E
%FWHM
te
(ns)
e
(mrad)
Inst. Stop rate (s-1)
Duty cycle (%)
Result
SIN (PSI)
A. Van der Schaaf
1977 8.7 9.3 1.4 - (4..6) x 105 100 < 1.0 10-9
TRIUMFP.
Depommier1977 10 8.7 6.7 - 2 x 105 100 < 3.6 10-9
LANLW.W.
Kinnison1979 8.8 8 1.9 37 2.4 x 105 6.4 < 1.7 10-10
Crystal Box
R.D. Bolton 1986 8 8 1.3 87 4 x 105 (6..9) < 4.9 10-11
MEGA M.L. Brooks 1999 1.2 4.5 1.6 17 2.5 x 108 (6..7) < 1.2 10-11
MEG ? ? ? ? 3 x 107 100 ~ 10-13
26 June '07 Particle Colloquium Heidelberg 32
The MEGA Experiment
• Detection of in pair spectrometer• Pair production in thin lead foil
• Good resolution, but low efficiency (few %)
• Goal was 10-13, achieved was 1.2 x 10-11
• Reason for problems:• Instantaneous rate 2.5 x 108 m/s
• Design compromises
• 10-20 MHz rate/wire
• Electronics noise & crosstalk
• Lessons learned:• Minimize inst. rate
• Avoid pair spectrometer
• Carefully design electronics
• Invite MEGA people!
26 June '07 Particle Colloquium Heidelberg 33
Photon Detectors (@ 50 MeV)
• Alternatives to Pair Spectrometer:
• Anorganic crystals:– Good efficiency, good energy resolution,
poor position resolution, poor homogeneity– NaI (much light), CsI (Ti,pure) (faster)
• Liquid Noble Gases:– No crystal boundaries– Good efficiency, resolutions
25 cm CsI
induced shower
Density 3 g/cm3
Melting/boiling point 161 K / 165 k
Radiation length 2.77 cm
Decay time 45 ns
Absorption length > 100 cm
Refractive index 1.57
Light yield 75% of NaI (Tl)
Liquid Xenon:CsI CsI
PMTPMTPMT
26 June '07 Particle Colloquium Heidelberg 34
Liquid Xenon Calorimeter
• Calorimeter: Measure Energy, Positionand Time through scintillation light only
• Liquid Xenon has high Z and homogeneity
• ~900 l (3t) Xenon with 848 PMTs(quartz window, immersed)
• Cryogenics required: -120°C … -108°
• Extremely high purity necessary:1 ppm H20 absorbs 90% of light
• Currently largest LXe detector in theworld: Lots of pioneering work necessary
Liq. Xe
H.V.
Vacuum
for thermal insulation
Al Honeycombwindow
PMT
Refrigerator
Cooling pipe
Signals
fillerPlastic
1.5m
26 June '07 Particle Colloquium Heidelberg 35
• Light is distributed over many PMTs
• Weighted mean of PMTs on front face x
• Broadness of distribution Dz
• Position corrected timing Dt
• Energy resolution depends on light attenuation in LXe
LXe 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
x
z
26 June '07 Particle Colloquium Heidelberg 36
• Light is distributed over many PMTs
• Weighted mean of PMTs on front face x
• Broadness of distribution z
• Position corrected timing t
• Energy resolution depends on light attenuation in LXe
LXe 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
x
z
26 June '07 Particle Colloquium Heidelberg 37
• Use GEANT to carefully study detector
• Optimize placement of PMTs according to MC results
26 June '07 Particle Colloquium Heidelberg 38
LXe Calorimeter Prototype
¼ of the final calorimeter was build to study performance, purity, etc.
240 PMTs240 PMTs
26 June '07 Particle Colloquium Heidelberg 39
How to get 50 MeV ’s?
• - p 0 n (Panofsky) 0
• LH2 target• Tag one with NaI & LYSO
• - p 0 n (Panofsky) 0
• LH2 target• Tag one with NaI & LYSO
26 June '07 Particle Colloquium Heidelberg 40
Resolutions
• NaI tag: 65 MeV < E(NaI) < 95 MeV
• Energy resolution at 55 MeV:(4.8 ± 0.4) % FWHM
• LYSO tag for timing calib.:260 150 (LYSO) 140 (beam)= 150 ps (FWHM)
• Position resolution:9 mm (FWHM)
FWHM = 4.8%FWHM = 4.8%
FWHM = 260 ps
FWHM = 260 psTo be improved with refined
analysis methods
To be improved with refinedanalysis methods
26 June '07 Particle Colloquium Heidelberg 41
Lessons learned with Prototype
• Two beam tests, many -source and cosmic runs in Tsukuba, Japan
• Light attenuation much too high (~10x)
• Cause: ~3 ppm of Water in LXe
• Cleaning with “hot” Xe-gas before filling did not help
• Water from surfaces is only absorbed in LXe
• Constant purification necessary
• Gas filter system (“getter filter”) works, attenuation length can be improved, but very slowly ( ~350 hours)
• Liquid purification is much faster
First studies in 1998, final detector ready in 2007First studies in 1998, final detector ready in 2007
26 June '07 Particle Colloquium Heidelberg 42
Xenon storage
~900L in liquid, largest amount of LXe ever liquefied in the world
LXe CalorimeterLiquid circulating purifier
Liquid pump (100L/h)
Purifier1000L storage dewar
Cryocooler (100W)
LN2
LN2
Getter+Oxysorb
GXe pump (10-50L/min)
GXe storage tank
Cryocooler (>150W)
Heat exchanger
26 June '07 Particle Colloquium Heidelberg 43
Final Calorimeter
Currently being assembled, will go into operation summer ‘07
26 June '07 Particle Colloquium Heidelberg 44
Positron Spectrometer
Ultra-thin (~3g/cm2) superconducting solenoid with 1.2 T magnetic field
Homogeneous Field
e+ from +e+e+ from +e+
Gradient Field(COnstant-Bending-RAdius)
high pt track constant |p| tracks
26 June '07 Particle Colloquium Heidelberg 45
Drift Chamber
• Measures position, time and curvature of positron tracks
• Cathode foil has three segments in a vernier pattern Signal ratio on vernier strips to determine coordinate along wire
26 June '07 Particle Colloquium Heidelberg 46
Positron Detection System
• 16 radial DCs with extremely low mass
• He:C2H6 gas mixture
• Test beam measurementsand MC simulation:
• p/p = 0.8%
• = 10 mrad
• xvertex = 2.3 mm
FWH
M
26 June '07 Particle Colloquium Heidelberg 47
Timing Counter
• Staves along beam axis for timing measurement
• Resolution 91 ps FWHM measured at Frascati e- - beam
• Curved fibers with APD readout for z-position
• Staves along beam axis for timing measurement
• Resolution 91 ps FWHM measured at Frascati e- - beam
• Curved fibers with APD readout for z-position
Timing resolution of BC 404
70
75
80
85
90
95
100
105
-40 -30 -20 -10 0 10 20 30 40
distance from center (cm)
90 deg
65 deg
53 deg
40 deg
Goal
Experiment Size [cm] Scintillator
PMT att [cm] FWHM[ps]
G.D. Agostini 3 x 15 x 100 NE114 XP2020 200 280
T. Tanimori 3 x 20 x 150 SCSN38 R1332 180 330
T. Sugitate 4 x 3.5 x 100 SCSN23 R1828 200 120
R.T. Gile 5 x 10 x 280 BC408 XP2020 270 260
TOPAZ 4.2 x 13 x 400
BC412 R1828 300 490
R. Stroynowski
2 x 3 x 300 SCSN38 XP2020 180 420
BELLE 4 x 6 x 255 BC408 R6680 250 210
MEG 4 x 4 x 90 BC404 R5924 270 90
26 June '07 Particle Colloquium Heidelberg 48
The complete MEG 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
26 June '07 Particle Colloquium Heidelberg 49
MC Simulation of full detector
e+
TC hit
“Soft” s
26 June '07 Particle Colloquium Heidelberg 50
Beam induced background
108 /s produce 108 e+/s produce 108 /s
Cable ductsfor Drift Chamber
26 June '07 Particle Colloquium Heidelberg 51
Detector Performance
•Prototypes of all detectors have been built and tested
• Large Prototype Liquid Xenon Detector (1/4)
• 4 (!) Drift Chambers
• Single Timing Counter Bar
•Performance has been carefully optimized
• Light yield in Xenon has been improved 10x
• Timing counter 1 ns 100 ps
• Noise in Drift Chamber reduced 10x
•Detail Monte Carlo studies were used to optimize material
•Continuous monitoring necessary to ensure stability!
26 June '07 Particle Colloquium Heidelberg 52
Sensitivity and Background Rate
Aimed experiment parameters:
N 3 107 /s
T 2 107 s (~50 weeks)
/4 0.09
e 0.90
0.60
sel 0.70
FWHM
Ee 0.8%
E 5%
e 18 mrad
te 180 ps
Single event sensitivity (N • T • /4 • e • • sel )-1 = 3.6 10-14
Prompt Background Bpr 10-17
Accidental Background Bacc Ee • te • (E)2 • (e)2 4 10-14
90% C.L. Sensitivity 1.3 10-13
Aimed resolutions:
26 June '07 Particle Colloquium Heidelberg 53
Current resolution estimates
Exp./Lab
Author Year Ee/Ee
%FWHM
E/E
%FWHM
te
(ns)
e
(mrad)
Inst. Stop rate (s-1)
Duty cycle (%)
Result
SIN (PSI)
A. Van der Schaaf
1977 8.7 9.3 1.4 - (4..6) x 105 100 < 1.0 10-9
TRIUMFP.
Depommier1977 10 8.7 6.7 - 2 x 105 100 < 3.6 10-9
LANLW.W.
Kinnison1979 8.8 8 1.9 37 2.4 x 105 6.4 < 1.7 10-10
Crystal Box
R.D. Bolton 1986 8 8 1.3 87 4 x 105 (6..9) < 4.9 10-11
MEGA M.L. Brooks 1999 1.2 4.5 1.6 17 2.5 x 108 (6..7) < 1.2 10-11
MEG 2008 0.8 4.3 0.18 18 3 x 107 100 ~ 10-13
26 June '07 Particle Colloquium Heidelberg 54
Current sensitivity estimation
• Resolutions have beenupdated constantly to seewhere we stand
• Two international reviewsper year
• People are convinced thatthe final experiment canreach 10-13 sensitivity
http://meg.web.psi.ch/docs/calculator/
26 June '07 Particle Colloquium Heidelberg 55
How to address pile-up
• Pile-up can severely degrade the experiment performance!
• Traditional electronics cannot detect pile-up
TDC
Amplifier Discriminator Measure Time
Need fullwaveform digitization
to reject pile-up
Need fullwaveform digitization
to reject pile-up
26 June '07 Particle Colloquium Heidelberg 56
• Need 500 MHz 12 bit digitization for Drift Chamber system
• Need 2 GHz 12 bit digitization for Xenon Calorimeter + Timing Counters
• Need 3000 Channels
• At affordable price
Waveform Digitizing
Solution: Develop own“Switched Capacitor Array” Chip
Solution: Develop own“Switched Capacitor Array” Chip
26 June '07 Particle Colloquium Heidelberg 57
The Domino Principle
Shift RegisterClock
IN
Out
“Time stretcher” GHz MHz“Time stretcher” GHz MHz
Waveform stored
Inverter “Domino” ring chain0.2-2 ns
FADC 33 MHz
Keep Domino wave running in a circular fashion and stop by trigger Domino Ring Sampler (DRS)
Keep Domino wave running in a circular fashion and stop by trigger Domino Ring Sampler (DRS)
26 June '07 Particle Colloquium Heidelberg 58
The DRS chip3
2 c
han
nels
in
pu
t
• DRS chip developed at PSI
• 5 GHz sampling speed, 12 bits resolution
• 12 channels @ 1024 bins on one chip
• Typical costs ~60 € / channel
• 3000 Channels installed in MEG
• Licensing to Industry (CAEN) in progress
• DRS chip developed at PSI
• 5 GHz sampling speed, 12 bits resolution
• 12 channels @ 1024 bins on one chip
• Typical costs ~60 € / channel
• 3000 Channels installed in MEG
• Licensing to Industry (CAEN) in progress
26 June '07 Particle Colloquium Heidelberg 59
Waveform examples
“virtual oscilloscope”“virtual oscilloscope” pulse shape discriminationpulse shape discrimination
original:
firstderivation:
t = 15ns
Crosstalk removal by subtracting empty channelCrosstalk removal by subtracting empty channel
Quantum Step in Technology!
Quantum Step in Technology!
26 June '07 Particle Colloquium Heidelberg 60
DAQ System Principle
Active Splitter
Drift Chamber Liquid Xenon Calorimeter Timing Counter
WaveformDigitizing
Trigger
TriggerEvent number
Event type
Busy
Rack PC
Rack PC
Rack PC
Rack PC
Rack PC
opticallink
(SIS3100)
Rack PC
Rack PC
Rack PC
Rack PC
Event Builder
Switch
GBit Ethernet
LVDS parallel bus
VME VME
26 June '07 Particle Colloquium Heidelberg 61
DAQ System
• Use waveform digitization (500 MHz/2 GHz) on all channels
• Waveform pre-analysis directly in online cluster (zero suppression, calibration) using multi-threading
• MIDAS DAQ Software
• Data reduction: 900 MB/s 5 MB/s
• Data amount: 100 TB/year
• Use waveform digitization (500 MHz/2 GHz) on all channels
• Waveform pre-analysis directly in online cluster (zero suppression, calibration) using multi-threading
• MIDAS DAQ Software
• Data reduction: 900 MB/s 5 MB/s
• Data amount: 100 TB/year
2000 channelswaveform digitizing
DAQ cluster
Monitoring
How to keep the experiment stable?
26 June '07 Particle Colloquium Heidelberg 63
Long time stability
• Especially the calorimeter needs to run stably over years
• Primary problem: Gain drift of PMT might shift background event into signal region
• If we find e , are we sure it’s not an artifact?
• Need sophisticated continuous calibration!
• Unfortunately, there is no 52.8 MeV source available
E[MeV]
N 52.8 MeV
e
e
26 June '07 Particle Colloquium Heidelberg 64
Planned Calorimeter Calibrations
Combine calibration methods different in complexity and energy:
Method Energy Frequency
LED pulser ~few MeV Continuously241Am source on wire
5.6 MeV Continuously
n capture on Ni 9 MeV daily
p+ 7Li 17.6 MeV daily
0 production on LH2
54 – 82 MeV
monthly ?
LED100 m gold-plated tungsten wire
n 58Ni9 MeV
26 June '07 Particle Colloquium Heidelberg 65
7Li(p,)8Be Spectrum
7Li (p,)8Be resonant at Ep= 440 keV =14 keV peak = 5 mbE0 = 17.6 MeVE1 = 14.6 MeV 6.1 MeVBpeak 0/(0+ 1)= 0.72
7Li (p,)8Be resonant at Ep= 440 keV =14 keV peak = 5 mbE0 = 17.6 MeVE1 = 14.6 MeV 6.1 MeVBpeak 0/(0+ 1)= 0.72
NaI 12”x12” spectrumNaI 12”x12” spectrum
1
Crystal Ball DataCrystal Ball Data
0
26 June '07 Particle Colloquium Heidelberg 66
CW Accelerator
• 1 MeV protons• 100 A• HV
Engineering, Amersfoort, NL
• 1 MeV protons• 100 A• HV
Engineering, Amersfoort, NL
beam spot
+ -
p+
26 June '07 Particle Colloquium Heidelberg 67
0 Calibration
NaI
target
00
• Tune beam line to -
• Use liquid H2 target
• -p n
• Tag one with movable NaI counter
• Beamline & target change take ~1 day
• Tune beam line to -
• Use liquid H2 target
• -p n
• Tag one with movable NaI counter
• Beamline & target change take ~1 day
26 June '07 Particle Colloquium Heidelberg 68
Midas Slow Control Bus System
BTS Magnet LXe purifier LXe storage LXe cryostat NaI mover
COBRADC gas system A/C hut Cooling water VME Crates HV
Beamline
PC• All subsystems controlled by same MSCB system• All data on tape• Central alarm and history system• Also used now at: SR, SLS, nEDM, TRIUMF
• All subsystems controlled by same MSCB system• All data on tape• Central alarm and history system• Also used now at: SR, SLS, nEDM, TRIUMF
MSCB
HVR SCS-2000
Status and Outlook
Where are we, where do we go?
26 June '07 Particle Colloquium Heidelberg 70
Current Status
• Goal: Produce “significant” result before LHC
• R & D phase took longer than anticipated
• We are currently in the set-up and engineering phase, detector is expectedto be completed end of 2007
• Data taking will go 2008-2010
R&D
199920002001200220032004200520062007200820092010
Engineering
DataTaking
Set-up
http://meg.psi.chhttp://meg.psi.ch
26 June '07 Particle Colloquium Heidelberg 71
What next?
Will we find e ?
No
• Improve experiment from 10-13 to 10-14:
• Denser PMTs
• Second Calorimeter
• Improve experiment from 10-13 to 10-14:
• Denser PMTs
• Second Calorimeter
Yes
• Carefully check results
• Be happy
• Most extensions of the SM (SUSY, Little Higgs, Extra Dimensions)predict e
More experiments needed
• Carefully check results
• Be happy
• Most extensions of the SM (SUSY, Little Higgs, Extra Dimensions)predict e
More experiments needed
26 June '07 Particle Colloquium Heidelberg 72
“Polarized” MEG
• are produced already polarized
• Different target to keep polarization
• Angular distribution of decays predicteddifferently by different theories(compare Wu experiment for Parity Violation)
SU(5) SUSY-GUT A = +1SO(10) SUSY-GUT A 0MSSM with R A = -1
SU(5) SUSY-GUT A = +1SO(10) SUSY-GUT A 0MSSM with R A = -1
Detector acceptance
Y.Kuno et al.,Phys.Rev.Lett. 77 (1996) 434
2
cos1)(
cos
)( e
e
APeBR
d
edN
26 June '07 Particle Colloquium Heidelberg 73
Expected Distribution
• A = +1• B (+ e+ ) = 1 x 10-12
• 1 x 108 +/s• 5 x 107 s beam time (2 years)• P = 0.97
• A = +1• B (+ e+ ) = 1 x 10-12
• 1 x 108 +/s• 5 x 107 s beam time (2 years)• P = 0.97
S. Yamada @ SUSY 2004, Tsukuba
Signal +Background
Background
26 June '07 Particle Colloquium Heidelberg 74
Conclusions
• The MEG Experiment has good prospectives to improve the current limit for e by two orders of magnitude
• Pushing the detector technologies takes time
• The experiment is now starting up, so expect exciting results in 2008/2009
http://meg.psi.ch