Daisuke Kaneko,on behalf of the MEG(II) collaboration26 Aug, Moscow
Today and Tomorrow of the MEG experiment
Mu E Gamma• Little SM background via ν
oscillation
• Many beyond SM theories predict
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MEGexperiment
MEGA
SM + ν oscillation
example of SUSY
MEG 2013PRL110, 201801(2013)
E842 μ (g-2)PRD73(2006)072
Example of MSSMLarge tanβ & Heavy squarkIsidori et al, Phys. Rev. D 75, 115019 (2007)
Too Low to detect
Possibility to detect if exist
prediction from new physics
Signal and BackGround
SEVENTEENTH LOMONOSOV CONFERENCE ON ELEMENTARY PARTICLE PHYSICS
γ
Signal Event
μ+ e +
Accidental BG
μ+ e +νμνeγ μ+ e +
νμ
νeγ
Radiative Decay
event Eγ Ee+ Time Angle note
Signal
52.8 MeV 52.8 MeV Te = Tγ 180°
Acc BG
<52.8 MeV
≦52.8 MeV
uniform no correlate
Dominant BG
RD <52.8 MeV
<52.8 MeV
Te = Tγ ≦180° < 1/10 of Acc
Today :
MEG I experiment
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MEG at Paul Scherrer Institute• The world’s most intense μ
beam– 108 μ/s @ πE5 line
• DC current– Advantage to avoid accidental pile up
• Surface muon– Small momentum spread
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590 MeV, 2.2 mA, 1.3 MW, 50.6 MHz
PSI SμS proton ring cyclotron
~ 60 researchers from 5 countries
SINDRUM experiment(μ-e conv.) was done in the same place
MEG I instruments
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Liquid xenonγ-ray
detector
Timing counter
COBRA magnet with
Gradient B field
Low-massDrift
chamber
μ+ stopping
targetBeing
disassembled
MEG I steps
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2008 : First physics data taking
2010 : Result with 2008 data S = 1.3 x 10-11, UL = 2.8 x 10-11 (90% CL)
2011 : surpassed previous experiment Result with 2009+2010 data S = 1.6 x 10-12, UL = 2.4 x 10-12 (90% CL)
2013 : current world record Combined result 2009-2011 S = 7.7 x 10-13, UL = 5.7 x 10-13 (90% CL)
Phys. Rev. Lett. 107, 171801
Phys. Rev. Lett. 110, 201801
Integrated statistical amount
2013 : Finished data acquisition
2015 : final result of MEG I (expected)
Nucl. Phys. B, 834 1
×2
×2
×2
1 /
Sin
gle
Even
t Sensi
tivit
y
(10
-12)
Blindeddata
sensitivity
upper limit
Analysis of MEG data
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Best fit Nsig is estimated by likelihood fitting on analysis region.Confidence region is set by a frequentist method with a profile likelihood-ratio ordering
The analysis region is blinded until the PDFs for the likelihood analysis are finalized.The PDFs are extracted from side-band data or calibration data.
from MEG 2013 result
Analy
sis
regio
n
Tim
esi
de b
an
d
Tim
esi
de b
an
d
Eγside band
teγ[ns]
Eγ[MeV]
Constraints of NBG and NRD estimated from the sideband data
signalcontour1σ1.64σ2σ
MEG I final result
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In final MEG analysis, data amount is doubled.
In addition, analysis has been improved since previous analysis for 2013 result.
S ~ 7.7×10-13
S ~ 5×10-13
Reduction of BG-γ from annihilation in flight of positronWhen BG γ is generated by annihilation in tracker. It can be tagged by checking disappearing e+ track and γ hit point.
Positron missing turn recoveryImprove the efficiency to connect track-segments of multiple
turn e+ tracks, In a case where e+ turns more than once, if 1st and 2nd turn were
identified separately. A wrong vertex can be reconstructed.
Target alignment with 3D scannerIn 2012 and 2013 data, deformation of μ target was found.It is taken into account in vertex reconstruction and the
systematic error is included the likelihood function.
MEG I final result comes soon !
Tomorrow :
MEG II experiment
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MEG II concept
• 10 times better sensitivity, B ~ O(10-14) !
– Keep basic concept of experiment• upgrade with low cost, in short term
– Use full potential of PSI beam line• Higher μ+ intensity, ×2-3
– Improve detector performance• Overall efficiency ×2• Resolution /2
for all Eγ, Ee , teγ, θeγ and φeγ
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Over view of the detector upgrades
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thinnertarget
additionaldetector“RDC”
Liquid xenonread out with SiPM
Unified volumeStereo wiredDrift chamber
PixelatedTiming counter
ManySiPMs
xenon detector
timing counter
RDC
Upgraded γ detector
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Lesson from MEG I :
Improve uniformity of light collection especially when γ ray converts near inner wall.
PMT
MPPC
PMT
CG image
depth<2cm2.4%
↓1.1%
present
upgraded
depth from window [cm]
pos
itio
n r
esol
uti
on [
mm
]
presentupgraded
The energy and position resolutions will be greatly improved.
γ detection efficiency increases by 10%,thanks to low-mass of MPPC.
LXe MPPC
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New sensor has been developed in collaboration with Hamamatsu
2-inch PMT
Normal MPPC(3x3 mm2)
VUV MPPC(12x12 mm2)
>15% PDE for LXe scintillation light (λ ~ 175nm).
Four 6x6 mm2 chips are connected in series, in order to reduce sensor capacitance (, and thereby to get sharper signal).
A technology to suppress crosstalk is applied to the final version
1 kΩ
22nF
Status of γ-detector upgrade
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We performed prototype test with 600 MPPCs in Liquid Xenon.
Operation of MPPC, cable, connector, feedthrough etc.were confirmed.
Now, ~4000 pcs of final version MPPCs are being produced, and tested.
New Drift chamber
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Lesson from MEG I :
Many positrons were lost by hitting structure atthe end of the drift chamber.
timing counter
Scattered at the flame and readout board
Positron reconstruction efficiency
40% → 90%
・ Single volume・ Stereo wired
single hit resolution σ ~0.1mmmore detect points by finer cell
Angular resolution of e+ emission
9mrad → 5mradMomentum resolution
350 keV → 130 keV
timing counter
No extra materials between timing counter
Status of new Drift chamber
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・ Test of resolution and ageing with prototypes were already finished. ・ Full-scale and partially wired “mockup chamber” was made → tested in engineering run
・ Production of front-end electronics startedWiring machine Mockup delivered
New Timing counter
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MEG I TC : As much photoelectrons with large scintillator (PMT readout)
MEG II TC : Hit time measurement with multiple hits in segmented timing counter (SiPM readout)
High rate tolerance, better timing resolution σ~ 30ps Single Counter
6 series SiPMs (AdvanSiD) on both side
12cm
4/5
cm
t 5mm
average Nhit
Status of new TC
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Beam test was performed to demonstrate multi-hit scheme
e+
Prototype Counters
Beam test in PSI πE5 area Beam test result
Currently mass-production is underway.
1/4 of full detector will be tested in engineering run at end of this year.
Expected timing resolution is obtained
average Nhit
resolution of single detector is worse due to the performance of SiPM
Expectation from single resolutionRC AnalysisOdd–Even AnalysisRC Analysis with hit selection
Reference Counters
New Detector to reduce BG
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Low energy positron
Down-stream RDCplastic scintillator
+ LYSO
Up-stream RDCscintillation fiber
UnderConstructi
on
needs studyabout beam
disturbance
RadiativeDecayCounter
Developments in Electronics
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“WaveDREAM”
An integrated board with ・ Analog amplifier ・ HV supply ・ Waveform digitizer (DRS4) ・ 1st level trigger
16 channels in a board, 16 boards in a crate(3U),The first crate will be available in this autumn.
The number of readout channels will increase by more than factor 2.
MEG II Prospects
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After 3 years of data taking,Expected sensitivity is 4-5 x10-14
Schedule
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2015 2016 2017
Accelerator ONAccelerator OFFAccelerator ONAccelerator
OFF
construction
Engineeringrun preparation
μbeamDAQ
InstallationCalibration
Beam tuningCalibrationTest DAQ
Start MEG II physics runwhen we will get ready
Conclusion
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Thank you for your listening
MEG beam line
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μ-e
Separator
Beam Transportation Solenoid
gradient B field
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e+ quickly swept out.
Bending radius depends on emission angle on ly little.
Positron AIF
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AIF ObservablesΔθAIF, ΔφAIF, ΔtAIF :
Comparison of e+ &
γ
RAIF, ZAIF, φAIF :
Where AIF occurred
target
Liquid Xenon
Drift Chamber
Δθ,φ,tAIF
R,φ,ZAIF
ΔθAIF ΔφAIF ΔtAIF correctAIF pair
randomAIF pair
Signal RDsimulate
missing turn
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1st trun2nd trun
wrong vertex
true vertex
BG γ
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PDE of LXe MPPC
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crosstalk suppressionapplied
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