ミューオン崩壊で探る新物理 ~ MEG 実験 ...epp.phys.kyushu-u.ac.jp/documents/meg_kyusyu2011.pdf1 2 3 u d c s t b e ν μ ν τ ν mass scale generation H.Nishiguchi (KEK)

九州大学素粒子実験研究室セミナー, 22/Dec./2011

西口創, KEK素核研

ミューオン崩壊で探る新物理 ~ MEG 実験 ~

Contents✤ Lepton Flavour Violation✤ μ→eγ Decay Search✤ MEG Experiment✤ Latest Results✤ Future Prospects

2

H.Nishiguchi (KEK) “ミューオン崩壊で探る新物理 - MEG -” 九州大学素粒子実験研究室セミナー 22.Dec.2011

Lepton Flavour Violation

Particle’s Flavour Violation4

1 2 3

u

d

c

s

t

b

e

ν

μ

ν

τ

ν

mas

s sc

ale

generation



1 2 3

u

d

c

s

t

b

e

ν

μ

ν

τ

ν

mas

s sc

ale

generation

Quark Sector• Mixed by CKM mechanism• Experimentally Verified

➡ B factories



1 2 3

u

d

c

s

t

b

e

ν

μ

ν

τ

ν

mas

s sc

ale

generation


➡ B factories

neutral Lepton Sector• Neutrino Oscillation • Experimentally Verified

➡ SK, SNO, KamLAND, etc.



1 2 3

u

d

c

s

t

b

e

ν

μ

ν

τ

ν

mas

s sc

ale

generation


➡ B factories

neutral Lepton Sector• Neutrino Oscillation • Experimentally Verified

➡ SK, SNO, KamLAND, etc.

charged Lepton Sector• source from beyond SM ??• never observed yet !!?

?


Why charge LFV has never been observed ?5

SM + simple ν Oscillation• charged LFV is possible

• but extremely rare (small ν)

• B(μ→eγ) = 10-50 ~10 -40 !!!

μ e

w

ν oscill.

γe.g.


Why charge LFV has never been observed ?5

SM + simple ν Oscillation• charged LFV is possible

• but extremely rare (small ν)

• B(μ→eγ) = 10-50 ~10 -40 !!!

μ e

w

ν oscill.

γe.g.

beyond SM (SUSY-GUT etc.)

• charged LFV is largely enhanced

• still rare but observable level

• B(μ→eγ) = 10-15 ~10 -11 !!!

μ e

γ

χ0μ e

e.g.


Why charged LFV is Attractive ?6

Only charged LFV has never been observed

Neutrino Oscillation is possible by “SM + ν mass”

Quark Mixing is generally contaminated by SM

➡ charged LFV is “NEW PHYSICS”

Experimental Upper Limit is already sensitive to predicted region

e.g. μ→eγ is the most sensitive mode to search for charged LFV

Muon can be generated most easily. → Suitable for rare decay search experiment.


Scenarios -1-7

✤ Supersymmetric Standard Model; The most well motivated model✤ Induced by slepton mixing

(1)Supersymmetric Standard Model

!"#$%&'()*+,-#.%+/#,&0#123-()-#45,'('56&-

7,'8)&'#93#-:&16+,#/(;(,<

=;)25,<(,<#5#12+6+,############################.+8%#.&%/(#+1&%56+%-#5%&#(,'8)&'#>>>#12+6+,#1&,<8(,

?@&,#(6#'+/(,56&-A

(1)Supersymmetric Standard Model

!"#$%&'()*+,-#.%+/#,&0#123-()-#45,'('56&-

7,'8)&'#93#-:&16+,#/(;(,<

=;)25,<(,<#5#12+6+,############################.+8%#.&%/(#+1&%56+%-#5%&#(,'8)&'#>>>#12+6+,#1&,<8(,

?@&,#(6#'+/(,56&-A✤ Supersymmetric Models with See-Saw Mechanism✤ Large slepton mixing is induced through renormalization

!"#$%&&&&&&&&&&&&&&&&&&'$()#$*$&&&

+$#,-&./-01)*&2"3"*,&".&"*45%-4&16#)5,6&#-*)#2$/"7$8)*&&&

9)#152$8&$*4&'$."-#)&&&

:".$*)&$*4&;)25#$&&&

- Hisano, Moroi, Tobe, Yamaguchi (1996)- Barbieri, Hall (1994)

- Hisano, Nomura (1999)- Borzumati, Masiero (1986)


Scenarios -2-8

✤ Little Higgs Model with T-Parity

✤ Exchange of the T-odd gauge bosons and the T-odd fermions

✤ Misalignment of physical base against flavour base

(2)Little Higgs Model with T Parity

!"#$%&'()'!*+#,'-.'/.)'0*"1$2'!)'34,56&$+1&7&+'-)'8#+#$9$4

:;56#$2&'4<'86&'8=477'2#*2&'>4,4$,')

(1,#"12$?&$@''4<'A6B,15#"'>#,&'#2#1$,@'C#D4+'>#,&

#$7'@6&'8=477'<&+?14$,

!4;'71#2+#?''#$7'E'A&$2*1$@4'<4*+'<&+?1'1,'"#+2&'

- Blanke, Buras, Duling, Poschenrieder, Tarantino

✤ Extra dimensional models✤ Anarchic RS model

✤ Fermions are located in different plane in 5D to explain Yukawa’s Non-universal coupling to KK gauge bosons even in flavour base

(2) Extra dimensional models

!"#$%&'()*&+%,#-'(.&/01&**2

#3(!-#0+%1+(45(,26&*

71$#*1"-,&-/((28(9%:$1+#*(;#$&(#"#1-$/(<#=20(;#$&

>&0,12-$(#0&(*2+#/&6(1-(61?&0&-/(9*#+&(1-(@A(/2(&B9*#1-(CDE#F#G$H2-ID-1=&0$#*(+2D9*1-"(/2(JJ("#D"&(;2$2-$(&=&-(1-(<#=20(;#$&K(

LB+%#-"&(28(JJ("#D"&(;2$2-$((+#D$&$(%D"&(M>N

K(61?&0&-/(&#+%(2/%&0

K(1-(,#$$(;#$&

OP(Q&N(1$(F1/%1-(#(0&#+%(RR

- Agashe, Blechman, PetrielloH.Nishiguchi (KEK) “ミューオン崩壊で探る新物理 - MEG -” 九州大学素粒子実験研究室セミナー 22.Dec.2011

Which is the best probe ?9

78 W. Altmannshofer et al. / Nuclear Physics B 830 (2010) 17–94

Table 8“DNA” of flavour physics effects for the most interesting observables in a selection of SUSY and non-SUSY models

signals large effects, visible but small effects and implies that the given model does not predictsizable effects in that observable.

AC RVV2 AKM !LL FBMSSM LHT RS

D0 ! D0 ?

"K

S#$

S$KS?

ACP(B " Xs% ) ?

A7,8(B " K#µ+µ!) ?

A9(B " K#µ+µ!) ?

B " K(#)&&

Bs " µ+µ!

K+ " '+&&

KL " '0&&

µ " e%

( " µ%

µ + N " e + N

dn

de

(g ! 2)µ ?

RVV2, AKM) and (LHT, RS) models can easily be made with the help of BR(Bs " µ+µ!) andBR(K+ " '+&&) only but the inclusion in this test of S#$ will be very helpful. The distinctionbetween the AC and RVV2 models has been discussed in the previous sections while the onebetween LHT and RS in [16,77]. Here the correlation between KL " '0&& and K+ " '+&&

markedly different in both models and the hierarchy in (7.1) could play important roles.

7.2. DNA-flavour test of new physics models

We have seen in the previous sections and in Section 7.1 that the patterns of flavour violationfound in various extensions of the SM differed from model to model, thereby allowing in thefuture to find out which of the models considered by us, if any, can survive the future measure-ments. Undoubtedly, the correlations between various observables that are often characteristicfor a given model will be of the utmost importance in these tests.

In Table 8, we show a summary of the potential size of deviations from the SM results allowedfor a large number of observables considered in the text, when all existing constraints from otherobservables not listed there are taken into account. We distinguish among:

✤ Anatomy and phenomenology of FCNC and CPV effects in SUSY theories

Nucl. Phys. B830 (2010) pp. 17-94


Which is the best probe ?9

78 W. Altmannshofer et al. / Nuclear Physics B 830 (2010) 17–94

Table 8“DNA” of flavour physics effects for the most interesting observables in a selection of SUSY and non-SUSY models

signals large effects, visible but small effects and implies that the given model does not predictsizable effects in that observable.

AC RVV2 AKM !LL FBMSSM LHT RS

D0 ! D0 ?

"K

S#$

S$KS?

ACP(B " Xs% ) ?

A7,8(B " K#µ+µ!) ?

A9(B " K#µ+µ!) ?

B " K(#)&&

Bs " µ+µ!

K+ " '+&&

KL " '0&&

µ " e%

( " µ%

µ + N " e + N

dn

de

(g ! 2)µ ?

RVV2, AKM) and (LHT, RS) models can easily be made with the help of BR(Bs " µ+µ!) andBR(K+ " '+&&) only but the inclusion in this test of S#$ will be very helpful. The distinctionbetween the AC and RVV2 models has been discussed in the previous sections while the onebetween LHT and RS in [16,77]. Here the correlation between KL " '0&& and K+ " '+&&

markedly different in both models and the hierarchy in (7.1) could play important roles.

7.2. DNA-flavour test of new physics models

We have seen in the previous sections and in Section 7.1 that the patterns of flavour violationfound in various extensions of the SM differed from model to model, thereby allowing in thefuture to find out which of the models considered by us, if any, can survive the future measure-ments. Undoubtedly, the correlations between various observables that are often characteristicfor a given model will be of the utmost importance in these tests.

In Table 8, we show a summary of the potential size of deviations from the SM results allowedfor a large number of observables considered in the text, when all existing constraints from otherobservables not listed there are taken into account. We distinguish among:

✤ Anatomy and phenomenology of FCNC and CPV effects in SUSY theories

Nucl. Phys. B830 (2010) pp. 17-94

All models are sensitive to these 2 processes !!


μ→eγ Decay Searchand

MEG Experiment

Two Major Muon LFV Processes11

e-N

μ -

e+

μ +

γ

μ→eγ μN→eN


History of μ→eγ Search Experiment12

✤ Long Tradition on the μ→eγ Search Experiment

✤ Started right after the muon discovery

✤ μ→eγ has already entered the predicted region !!

✤ NOW VERY VERY ATTRACTIVE !!!!!

Upp

er L

imit

on B

ranc

hing

Rat

io

10-15

10-13

10-11

10-9

10-7

10-5

10-3

10-1

1950 1970 1990 2010


Past μ→eγ Experiments

Previous Upper Limit (1999)

Best Limit on μ→eγ BR (2011)

Expected Reach on μ→eγ BR

History of μ→eγ Search Experiment12

✤ Long Tradition on the μ→eγ Search Experiment

✤ Started right after the muon discovery

✤ μ→eγ has already entered the predicted region !!

✤ NOW VERY VERY ATTRACTIVE !!!!!

Upp

er L

imit

on B

ranc

hing

Rat

io

10-15

10-13

10-11

10-9

10-7

10-5

10-3

10-1

1950 1970 1990 2010


Predicted Region for μ→eγ

Past μ→eγ Experiments

Previous Upper Limit (1999)

Best Limit on μ→eγ BR (2011)

Expected Reach on μ→eγ BR

Hunting for μ→eγ ✤ Signal and Backgrounds

✤ Clear 2-body kinematics (Ee=Eγ=52.8MeV, θeγ=180°, Time Coincidence)

✤ Sensitivity is Limited by “Accidental Overlap”

✤ DC muon is the Best Solution

✤ Good Resolution (Energy, Spacial and Timing) under Very High Rate

13

Sign

al

Prom

pt B

G.

Accid

enta

l BG.


Features of MEG14

✤ Sensitivity is Limited by “Accidental Overlap”

✤ DC muon is the Best Solution

✤ Good Resolution (Energy, Spacial and Timing) under Very High Rate

World Most Intense DC Muon Beam at PSI

108 muon/sec

Liquid Xenon Scintillation Detector

(gamma)

COBRA Spectrometer(positron)


PSI and its Cyclotron Facility15






MEG Detector Apparatus16

(1) World’s Most Intense DC Muon Beam

(2) Specially Graded Solenoidal Magnet

(3) Very LIGHT and Sensitive DC, and Very Fast TC

(4) Liquid Xenon Scintillation Photon Detector

The MEG Collaboration( 5 countries ,/12 institutes / ~60 persons )


Liquid Xenon Scintillation γ Detector17

✤ Homogeneous Volume ( ~800l ) is surrounded by PMTs on all faces

✤ 846 PMTs submerged in the liquid✤ Energy Measurement

✤ All PMT outputs✤ σE/E ~ 2% (@52.8MeV)

✤ Position Measurement✤ PMTs on the inner face✤ σx = 5-6 mm (@52.8MeV)

✤ Timing Measurement✤ Averaging of signal arrival time

of selected PMTs✤ σt ~ 70 ps (@52.8MeV)

!"#$%&&'()*$#&+'&%,&-$../.01$23.31$456786$9)7'('6'&$:;$<&=8):>:*5$$$$$<:78(56?($9@A%:':$..B#&+'&%,&-B23.3

.3

Liquid Xenon Detector! 900 liter liquid xenon ! 846 2” PMTs (Hamamatsu R9869)

" immersed in LXe directly

! Good uniformity ( homogeneous, liquid )! High light output ( ~75% of NaI )! Short decay time ( 45ns )! High density (3g/cm3)

! Short scintillation wavelength ~ 175nm" Quartz window for PMT

! Low temperature 165K" pulse tube cryocooler developed by KEK

! Purification to remove H2O, O

2, N

2 etc.

.C+#D/CE$DFG HI$JKLMNOPQRSTU E VW


COBRA Positron Spectrometer18

Solenoid

superconducting solenoid gradient B-field (0.5-1.7 T) very thin conductor and cryostat wall (0.2X0)

Drift Chamber

segmented radially (16 sectors) helium:ethane (50:50) opened-frame very thin cathode foil with pads

Timing Counter

2-layers of scintillators - scintillator bars (outer) - scintillator fibres (inner)


MEG History19

2007

2008

2009

2010

2011

JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC

Detector Construction / InstallationBeam Line Commissioning

Engineering / Pilot Run

Detector Maintenance / Minor Upgrades

Beam Line Commissioning

Conditioning / Calibration Runs1st Physics Run

Detector Maintenance / Minor UpgradesConditioning / Calibration Runs

2nd Physics Run1st Result(Prelimnl.)

Detector Maintenance / Repairs / Minor UpgradesCalibrations 3rd Physics Run

Calib. Repairs

4th Physics RunDetector Maintenance

2nd+3rd Result

2nd Result(Prelimnl.)

1st Result(Final)


MEG Run2008 (1st Physics Run)20

✤ Severe Problem on DC discharge✤ e+ efficiency/resolution

✤ Crisis...✤ Trigger efficiency

✤ Only ~14%...

✤ 12/Sep.-16/Dec. MEG Physics ✤ 8.4×1013 muon stops✤ but very poor efficiency...

✤ Final Result (2008) ;✤ B(μ→eγ) < 2.8×10-11 (90CL.)

✤ (sensitivity : 1.3×10-11 )✤ Nucl.Phys. B 834 (2010) 1-12


2008 2009

γ Energy σEγ (%) 2.0 (depth>2cm) 1.9γ Timing σtγ (ps) 80 96γ Position σxγ (mm) 5/6 ←

γ Efficiency εγ (%) 63 58e+ Mom. σpe (%) 1.6 (80%core) 0.59

e+ Timing σte (ps) <125 107e+ Angle σθe (mrad) 10(φ)/18(θ) 6.7(φ)/9.4(θ)e+ Efficiency εe (%) 14 40γ-e+ Relative Timing 148 146μ+ decay vertex (mm) 3.2/4.5 1.5/1.1Trigger Efficiency (%) 66 91μ+ Stopping Rate (Hz) 3×107 2.9×107

DAQ Time (days) 48 (78) 35 (43)Sensitivity 1.3×10-11 0.92×10-12

BR Upper Limit 2.8×10-11 coming soon

21

✤ Several Big Improvements✤ e+ efficiency/resolution

✤ Thanks to solving discharge problem

✤ Trigger efficiency

✤ DAQ time is shorter than 2008 due to other experiment sharing area

✤ Statistics-2009 : ～2×2008

✤ Compensated by efficiency improvements

MEG Run2009 (2nd Physics Run)


2008 2009 2010

γ Energy σEγ (%) 2.0 (depth>2cm) 1.9 ←

γ Timing σtγ (ps) 80 96 67γ Position σxγ (mm) 5/6 ← ←

γ Efficiency εγ (%) 63 58 59e+ Mom. σpe (%) 1.6 (80%core) 0.59 0.62

e+ Timing σte (ps) <125 107 ←

e+ Angle σθe (mrad) 10(φ)/18(θ) 6.7(φ)/9.4(θ) 7.2(φ)/11(θ)e+ Efficiency εe (%) 14 40 34γ-e+ Relative Timing 148 146 122μ+ decay vertex (mm) 3.2/4.5 1.5/1.1 2.0/1.1Trigger Efficiency (%) 66 91 92μ+ Stopping Rate (Hz) 3×107 2.9×107 ←

DAQ Time (days) 48 (78) 35 (43) 56 (67)Sensitivity 1.3×10-11 0.92×10-12 0.44×10-12

BR Upper Limit 2.8×10-11 coming soon coming soon

22

✤ Better Electronics Timing Accuracy by new digitizer (DRS4)

✤ Shorter Beamtime than planned

✤ Statistics : ～1.9×2009

MEG Run2010 (3rd Physics Run)


Analysis Procedure23

✤ Blind Analysis✤ Signal region was hidden until

analysis fixed ✤ Any study (calibration, BG

estimation, performance evaluation) can be done with events outside the box

✤ Hidden parameters (Eγ, Teγ)✤ Sideband Data

✤ Accidental BG can be studied with off-timing sideband data

✤ Radiative decay can be studied with low energy sideband data

✤ Normalization✤ Unbiased Michel data mixed in

physics data✤ Wide Analysis Region

✤ for likelihood fittingH.Nishiguchi (KEK) “ミューオン崩壊で探る新物理 - MEG -” 九州大学素粒子実験研究室セミナー 22.Dec.2011










✤ for likelihood fitting

Blind












BlindLeft Sideband

Right Sideband












BlindLeft Sideband

Right Sideband

Eγ Sideband


Likelihood Analysis24

✤ Fit Parameters : # of events Nsig, NRD and NBG (N=Nsig+NRD+NBG)✤ Observables : Energy Eγ, Ee, Relative time Teγ and Opening angle θeγ, φeγ

✤ Probability Density Function for each event type (S, R, B)✤ PDFs are extracted from data

✤ Fit in Wide region (10σ)✤ Fit Signal and Background simultaneously

✤ Three Independent Analysis Tools

✤ Extended unbinned maximum likelihood analysis on number of events

Different PDF implementation Fit or Input NRDDifferent Statistical treatment

(Frequentist or Bayesian)

check, understandingor find bug

L(Nsig, NRD, NBG)

=NNobse−N

Nobs

Nobs�

i=i

�Nsig

NS +

NRD

NR +

NBG

NB

�


PDFs - Energies, Angles and Timing -25

a.u.

Ee Signal PDF(from measured

resolution)

Ee BG PDF(from L/R sideband)

Eγ Signal PDF(from 55MeV γ)(using π0 beam)

Eγ BG PDF(from L/R sideband)

Teγ Signal PDF(from RD peak)

Relative Angle (θeγ, φeγ) PDF

Signal : from measured resolution

Background : from L/R sideband


Normalization - # of Muon Decay -26

✤ # of Michel Positrons is counted simultaneously using highly pre-scaled trigger applying the same event selection as for the physics data sample.

✤ Advantage: Independent of beam-rate & in 1st-order insensitive to acceptances & efficiencies (ratios)

✤ Branching ratio is represented by obtained normalization factor “k” and the # of signal which will be obtained by the final analysis

B(µ+ → e+γ)B(µ+ → e+νν)

=Nsig

Neνν× f e

eνν

P · �pu× �trigeνν

�trigeγ

× �DCeνν

�DCeγ

× 1Ageo

eγ× 1

�eγ

B(µ+ → e+γ) =k

Nsig


Experimental Sensitivity27

✤ Mean Upper Limit (90%C.L.) on ensemble of toy-MC experiments✤ Generate events with obtained PDFs assuming Null-Result Hypothesis ✤ Repeat toy-MC experiments and calculate Upper Limit for each

experiment in the same way as real data

✤ Signal-detection power of our likelihood analysis was also checked by dedicated toy-MC with mixed μ→eγ signal events


# of μ+ S.E.S. Expected Obtained

2008 9.5×1013 1.3×10-11 1.3×10-11 2.8×10-11

2009 6.0×1013 0.92×10-12 3.3×10-12

2010 1.2×1014 0.44×10-12 2.2×10-12

Sideband Fits28

✤ To confirm the final analysis, Off-timing Sideband data is fitted

Left Sideband

Right SidebandBlind


Finally.....29

✤ Signal Box is Blinded✤ Likelihood is Constructed✤ PDF is Built✤ Resolutions/Efficiencies are Evaluated✤ Background is Estimated✤ Normalization is Done✤ Experimental Sensitivity is Estimated✤ Everything is Confirmed in Sideband Fit

and thus...H.Nishiguchi (KEK) “ミューオン崩壊で探る新物理 - MEG -” 九州大学素粒子実験研究室セミナー 22.Dec.2011

Finally.....30

Now Ready to Open the BOX !!


Calorimeter sum WF

Spectrometer hits and a track

MEG Latest Results(Physics Data of 2009 and 2010)

2009 Unblinded Event Distribution32


2009 Event Distributions

ecos-1 -0.9995 -0.999 -0.9985 -0.998

(nse

c)et

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

21

3

76

9

(MeV)eE50 51 52 53 54 55 56

(MeV

)E

48

49

5051

52

53

54

5556

5758

2137

4

2009 data update

Nsig = 3.0 Nsig = 3.4

!"#"$%&'()!"#$!%&'()*+,-../#$0..1)*'23.4#5 61%7$%66.8#9-..6('23%7#%66.8#9

UL @90% C.L. = 9.6×10-12

2009 Event Distributions

ecos-1 -0.9995 -0.999 -0.9985 -0.998

(nse

c)et

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

21

3

76

9

(MeV)eE50 51 52 53 54 55 56

(MeV

)E

48

49

5051

52

53

54

5556

5758

2137

4

2009 data update

Nsig = 3.0 Nsig = 3.4

!"#"$%&'()!"#$!%&'()*+,-../#$0..1)*'23.4#5 61%7$%66.8#9-..6('23%7#%66.8#9

UL @90% C.L. = 9.6×10-12

Sample Event Display33

✤ Highest Ranked (=most signal-like) Event✤ No pileup, Relative Angle and Relative Timing are checked.✤ Every highly ranked events are checked carefully.

!"#$%&&'()*$#&+'&%,&-$../.01$23.31$456786$9)7'('6'&$:;$<&=8):>:*5$$$$$<:78(56?($9@A%:':$..B#&+'&%,&-B23.3

2C

Event display

Each highly ranked event is checked carefully.

Calorimeter sum WF Calorimeter PMT hit map

Spectrometer hits and a track

PMT sum WF

calorimeter PMT hit map

spectrometer hit & track


2009 Likelihood Fit / CL Curve34


BR < 9.6×10-12

(90CL.)

Teγ Ee Eγ

θeγ φeγ

totalacc.rad.sig.

2010 Unblinded Event Distribution35


ecos-1 -0.9995 -0.999 -0.9985 -0.998

(nse

c)et

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

1

(MeV)eE50 51 52 53 54 55 56

(MeV

)E

48

49

5051

52

53

54

5556

5758

2

2010 data unblinded on July 5th

!"#$!%&'()*+,--./+0#$%-1&'2223 45%6$%44-7#8,--4('9%6#%44-7#8

ecos-1 -0.9995 -0.999 -0.9985 -0.998

(nse

c)et

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

1

(MeV)eE50 51 52 53 54 55 56

(MeV

)E

48

49

5051

52

53

54

5556

5758

2

2010 data unblinded on July 5th

!"#$!%&'()*+,--./+0#$%-1&'2223 45%6$%44-7#8,--4('9%6#%44-7#8

2010 Likelihood Fit / CL Curve36


BR < 1.7×10-12

(90CL.)

Teγ Ee Eγ

θeγ φeγ

totalacc.rad.sig.

2009-2010 Combined37


2009 2010

BR(fit) LL(90CL)

UL(90CL)

2009 3.2×10-12 1.7×10-12 9.6×10-12

2010 -9.9×10-13 -- 1.7×10-12

2009+2010 -1.5×10-13 -- 2.4×10-12

MEG 2009-2010 Conclusion38


✤ MEG(2009+2010) is still consistent with Null Result

✤ BR(μ→eγ) < 2.4×10-12 (90%CL.)

✤ Best Upper Limit on BR(μ→eγ) is Updated for the 1st time in 12 years.

✤ Factor 5 restricted result !!

MEG Latest Result39


Future Topics

MEG 2011 (4th Physics Run)

✤ Finished on December/02.

✤ The 1st long term experiment, longer than 5 months

✤ approx. same statistics as “2009+2010”

✤ Analysis (Calibration / Performance Estimation / BG Estimation) is ongoing.

✤ Result will be presented in Summer 2012, as usual, hopefully.

41


MEG Prospect (within the 1st phase, ~2015)42

2008

2009

2010 2011 2012

data UL (2009+2010)

data UL (2009)

✤ RUN2009+2010 is present best limit

✤ RUN2011 will enter the O(~13) world

✤ Until RUN2012 will be same condition(＋minor UG）

✤ After RUN2013, several UG is planned

✤ eg. cable replacement in order to improve the position efficiency

✤ (nb. nothing is decided yet...)


MEG-2 (Improved MEG)43

✤ Bacc ∝ δEe × δteγ × (δEγ)2 × (δθeγ)2 ✤ 10 Times Better Sensitivity could be expected.

Detector Modifiable Item Possible Improvement

LXe CalorimeterHigh QE PMT δEγ×0.65 / δteγ×0.77

LXe CalorimeterFiner Granularity δθeγ×0.72 / Bacc×0.6

Drift Chamber Reduce Material δEe×0.8 / εe×1.25

General Double Acceptance Bacc×0.5


MEG-3 (Polarized MEG)44

✤ By the use of a polarized muon beam and a Suitable target, a polarized MEG can be performed.

✤ Based on a sufficient # of observed μ→eγ events, the positron angular distribution with respect to the muon spin orientation can be extracted and used to discriminate between different SUSY-GUT models.

the asymmetry of the e+ angular disribution

measuring the e+ emission angle distribution

polarized beam + depolarization target + MEG

MC study was performed to estimate feasibility

Possible to distinguish A = -1, 0, +1 at 68% C.L. for Br(µ+→e+γ) > 10-12.5 by a polarized MEG

A = +1A = -1

A = 0


Summary✤ Charged LFV is very attractive to explore the new physics beyond Standard Model.

✤ μ→eγ decay is the most sensitive to such a charged lepton flavour violation.✤ After longer than 60 years history, B(μ→eγ) achieved <1.2×10-11 (previous limit)

✤ MEG experiment started 2008 and is currently running in order to discover the first event of charged lepton flavour violation, in other words, evidence of new physics.✤ Run2008(1st) : B(μ→eγ) < 2.8×10-11 (very poor efficiency/resolution)✤ Run2009(2nd)

✤ 2×Run2008 Statistics (full efficiency)✤ Run2010(3rd)

✤ 1.9×Run2009 Statistics ✤ Combined Result : B(μ→eγ) < 2.4×10-12 (90CL.) (BEST LIMIT)✤ 5 times more restricted limit to the new physics

✤ Run2011(4th)✤ same statistics as “Run2009 + Run2010”✤ Analysis is ongoing

✤ MEG will achieve O(10-13) SOON and give us an important information, interesting and complemental with LHC.

45


Documents

ミューオン崩壊で探る新物理 ~ MEG 実験 ...epp.phys.kyushu-u.ac.jp/documents/meg_kyusyu2011.pdf1 2 3 u d c s t b e ν μ ν τ ν mass scale generation H.Nishiguchi (KEK)