Transcript Status of the MEG experiment 1 A. M. Baldini

MEG
Status of the
MEG experiment
http://meg.pi.infn.it
A. M. Baldini
INFN Pisa
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MEG
Layout of this talk
• Physics motivations
• General description of the
experiment
• Detectors R&D
• Sensitivity of the experiment
• Time schedule
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MEG
SUGRA indications
LFV induced by finite slepton mixing
through radiative corrections
Experimental limit
• SUSY SU(5) predictions
Our goal
BR (meg)  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
combined LEP results favour tanb>10
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MEG
Combined LEP experiments: SUGRA MSSM
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MEG
SO10
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MEG
Connection with n-oscillations
Additional contribution to slepton J. Hisano,
mixing from V21 (the matrix element
responsible for solar neutrino deficit)
N. Nomura, Phys. Rev. D59 (1999)
tan(b)=30
tan(b)=1
Experimental limit
After SNO
Our goal
R  10-54 in the Standard Model !!
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After
Kamland
MEG
m+  e+ g 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
~2005
~ 10-13
MEG
Two orders of magnitude improvement
is required:
tough experimental challenge!
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Comparison with other
LFV searches:
MEG
The MEG collaboration
INFN & Genova University S. Dussoni, F. Gatti, D. Pergolesi, R. Valle
INFN & Lecce University G. Cataldi, S. Spagnolo, C. Chiri, P. Creti, F.
Grancagnolo, M. Panareo
INFN & Pavia University A.de Bari, P. Cattaneo, G. Cecchet, G. Nardo’, M.
Rossella
INFN & Pisa University A. Baldini, C. Bemporad, F.Cei, M.Grassi, F. Morsani,
D. Nicolo’, R. Pazzi, F. Raffaelli, F. Sergiampietri, G. Signorelli
INFN Roma I D. Zanello
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
PSI, Villigen J. Egger, P. Kettle, H. Molte, S. Ritt
Budker Institute, Novosibirsk L.M. Barkov, A.A. Grebenuk, D.G. Grigoriev, B,
Khazin, N.M. Ryskulov
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MEG
Experimental method
Easy signal selection with m+ at rest
Detector outline
qeg = 180°
e+ m+
• Stopped beam of >107 m /sec
in a 150 mm target
g
• Liquid Xenon calorimeter for
g detection (scintillation)
Ee = Eg = 52.8 MeV
- fast: 4 / 22 / 45 ns
Liq. Xe Scintillation
Detector
Liq. Xe Scintillation
Detector
- high LY: ~ 0.8 * NaI
- short X0: 2.77 cm
Thin Superconducting Coil
g
Stopping Target
Muon Beam
e+
g
e+
Timing Counter
Drift Chamber
Drift Chamber
1m
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• Solenoid spectrometer &
drift chambers for e+
momentum
• Scintillation counters for e+
timing
MEG
Signal and background
signal
meg
background
accidental
menn
correlated
e+ m+
g
megnn
n
qeg = 180°
Ee = Eg = 52.8 MeV
e+ m+
n
Te = Tg
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g
megnn
ee  g g
eZ  eZ g
n
n
e+ m+
g
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MEG
Required Performances
The sensitivity is limited by the by the accidental background
BRacc  Rμ  ΔE e  ΔE γ2  Δθeγ2  Δteγ 310-14
The
allows BR (meg)  10-13 but needs
FWHM
Exp./Lab
Year
DEe/Ee
(%)
DEg /Eg
(%)
Dteg
(ns)
Dqeg
(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
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MEG
Detector Construction
Switzerland
Russia
Drift Chambers
Beam Line
DAQ
LXe Tests
Purification
Italy
Japan
e+ counter
Trigger
LXe Calorimeter
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LXe Calorimeter,
Magnetic spectrometer
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MEG
The PSI pE5 beam
Primary
proton
beam
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MEG
Beam studies
Optimization of the beam elements:
• Wien filter for m/e separation
• Solenoid to couple beam and spectrometer
• Degrader to reduce the momentum for a 150 mm target
Intermediate results:
•
•
•
•
U-version
Z-version
Rm (total)
1.3*108 m+/s
1.3*108 m+/s
Rm (after W.filter) 7.3*107 m+/s
9.5*107 m+/s
Rm (after solenoid) sV6.5mm, sH5.5mm to be studied
m/e separation
11 s
7s
Measurements on Z-branch are going on in 2003 Design of the
transport solenoid is started
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MEG
COBRA spectrometer
COnstant Bending RAdius (COBRA) spectrometer
• Constant bending radius independent of emission angles
Gradient field
Uniform field
• High pT positrons quickly swept out
Gradient field
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Uniform field
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MEG
Gradient field
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MEG
The solenoids
• Bc = 1.26T current = 359A
• Five coils with three different diameters
•“Crash” Tests completed
• Compensation coils to suppress the stray field
around the LXe detector
• High-strength aluminum stabilized superconductor •Winding completed @TOSHIBA
thin magnet
(1.46 cm Aluminum, 0.2 X0)
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•Ready to be shipped at PSI
during summer
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OK
MEG
Positron Tracker
• 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 mm kapton foils
s(X,Y) ~200 mm (drift time) s(Z) ~ 300 mm (charge division
vernier strips)
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MEG
Drift chambers R&D (1)
90Sr
source
Tokyo Univ.
s R  93  10 mm
s Z  425  7 mm
OK
(no magnetic field  full prototype test
at PSI by the end of this year)
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MEG
Drift chambers R&D
(2)
• Full scale test in November
• Improved vernier strips structure (more
uniform resolution)
FWHM
• Summary of Drift Chamber simulation
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Pe / Pe  0.7  0.9%


qe  9  12 mrad

xorig  2.1  2.5 mm
MEG
(90% C.L.) as a function of longitudinal position resolution
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MEG
Positron Timing Counter
BC404
• Two layers of scintillator read by PMTs placed at right angles with each other
Outer: timing measurement
Inner: additional trigger information
• Goal stime~ 40 psec (100 ps FWHM)
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MEG
Timing Counter R&D
CORTES: Timing counter test facility with
cosmic rays
s
• Scintillator bar (5cm x 1cm x 100cm long)
• Telescope of 8 x MSGC
• Measured resolutions
stime~60psec independent of incident position
• stime improves as ~1/√Npe  2 cm thick
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MEG
Liquid Xe calorimeter
•
•
•
•
•
800 l of Liquid Xe
~800 PMT immersed in LXe
Only scintillation light
High luminosity
Unsegmented volume
Refrigerator
H.V.
Signals
Cooling pipe
Experimental
check
Vacuum
for thermal insulation
Liq. Xe
Al Honeycomb
window
PMT
Plasticfiller
1.5m
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MEG
LXe performance
• Complete MC simulations
• At labs the resolution is
dominated by photostatistics
FWHM(E)/E  2.5% (including
edge effects)
FWHM(E)/E (%)
Energy resolution strongly depends on optical properties of LXe
• At labs Ldet limits from
shower fluctuations +
detector response  need of
reconstruction algorithms
FWHM(E)/E  4%
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MEG
Xenon Calorimeter Prototype
The Large Prototype (LP)
•40 x 40 x 50 cm3
•228 PMTs, 100 litres Lxe
(the largest in the World)
•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
with:
•
•
•
•
Cosmic rays
-sources
60 MeV eˉ from KSR storage ring
40 MeV g from TERAS Compton
Backscattering
• e+ and 50 MeV g from p° at PSI
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Planned in this year
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MEG
The LP
-sources
LEDs
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MEG
LP: LXe optical properties
•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 were a strong absorption due to contaminants (mainly H2O)
March 2002
Present...
labs> 1m
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MEG
LP: Radioactive background
• -trigger with 5106 gain
• Geometrical cuts to exclude sources
40K
(1.461 MeV)
• Energy scale: -source
•
208Tl
•
40K
(2.59±0.06) MeV
208Tl
(2.614 MeV)
(1.42 ± 0.06) MeV
• uniform on the front face
• few 10 min (with non-dedicated
trigger)
• nice calibration for low energy g’s
Seen for the first time! Studies are going on:
spatial distribution of background inside the
detector
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MEG
Timing resolution test
st = (sz2 + ssc2)1/2 = (802 + 602)1/2 ps = 100 ps (FWHM)
our goal
sz Time-jitter due to photon interaction point
ssc Scintillation time and photon statistics
Measurement of ssc2 with 60 MeV electron beam
• weighted average
of the PMT TDCs
time-walk corrected
• ssc vs
ph.el.
52.8 MeV peak
• extrapolation at
52.8 Mev is ok
• new PMT with QE
5 25%
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5%
10%
15%QE
MEG
Cryostat (PMT test facility)
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MEG
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MEG
Trigger Electronics
•Uses easily quantities:
LXe inner
face
(312 PMT)
•g energy
•Positron- g coincidence in time and
direction
•Built on a FADC-FPGA architecture
LXe lateral
faces
(488 PMT: 4
to 1 fan-in)
Type1
Type1
3 Type1
20 x 48
10 boards
Type1
Type1
3 Type1
g interaction point (PMT of max charge)
e+ hit point in timing counter
200 s-1
20 s-1
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4x
48
1 board
10 x 48
12 boards
 Beam rate
108 s-1
 Fast LXe energy sum > 45MeV 2103 s-1
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1 board
Type2
Timing
counters
(160 PMT)
2 boards
Type2
Type2
16
•More complex algorithms implementable
 time correlation g – e+
 angular correlation g – e+
20 boards
16
2 x 48
Type2
2 boards
2x
48
16
Type1
Type1
3 Type1
12 x 48
Type2
Type2
2 VME 6U
1 VME 9U
•Design and simulation of
type1 board completed
•Prototype board delivered
by late spring
MEG
Readout electronics
• 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
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Prototypes delivered in autumn
MEG
Sensitivity Summary
7
Detector parameters T  2.6 10 s
εe  0.9
Rμ  0.3 10 8 μ
εsel  0.9   0.7
3
Cuts at 1,4FWHM
Signal
Single Event
Sensitivity
Backgrounds
s
Ω
 0.09
4π
εγ  0.6

Nsig  BR T  Rμ 
  e   g   sel
4p
 410-14
SES  1

T  Rμ 
  e   g   sel
4p
BRacc  Rμ  ΔE e  ΔE γ2  Δθeγ2  Δteγ  210-14
BRcorr 310-15
Upper Limit at 90% CL BR (meg)  110-13
Discovery
4 events (P = 210-3) correspond BR = 210-13
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MEG
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 to meg (BR 10-13)
• Final prototypes will be measured within this year
• Large Prototype for energy, position and timing resolutions of gs
• Full scale Drift Chamber
• m-Transport and degrader-target
• Financed this year in Italy+Switzerland
• Tentative time profile
LoI Proposal
Planning
1998
1999
2000
Revised
document now
Assembly
R&D
2001
2003
2004
2005
2006
2007
http://meg.psi.ch
http://meg.pi.infn.it
http://meg.icepp.s.u-tokyo.ac.jp
More details at
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2002
Data Taking
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