1

MEG II — 10−14 µ+→ e+γ —

iekikei@icepp.s.u-tokyo.ac.jp uchiyama@icepp.s.u-tokyo.ac.jp

2018 ( 30 ) 4 30

1

PSIµ+ → e+γ MEG

2008–2013 [1][2]

30 B(µ+ → e+γ) < 4.2 × 10−13 (90%C.L.)

10 MEG II2012 [3] 2015

[4]µ+ → e+γ

52.8 MeV

MEG II

52.8 MeVµ+ → e+νeν̄µ

µ+ → e+νeν̄µγ

MEG II 1MEG

[2]

2 2

Liquid xenon photon detector(LXe)

Cylindrical drift chamber(CDCH)

COBRA superconducting g magnet

Radiative decay counter(RDC)

Muon stopping targett i t t

Pixelated timing counter(pTC)

Muon beam

Electronics

1: MEG II

2 10MEG II

MEG 1

10

LHC

µ+ → e+γ

10 1.8

[5]MEG II 5–10 TeV

LHCHL-LHC MEG II

MEG II

1

2

1: MEG II MEG

Resolution MEG MEG IIEe+ (keV) 380 90–130θe+ /φe+ (mrad) 9.4/8.7 5.5/4Eγ (%) (wγ < 2)/(wγ > 2 cm) 2.4/1.7 1.1/1.0uγ/vγ/wγa) (mm) 5/5/6 2.6/2.2/5te+γ (ps) 122 65–85Efficiency & Rateϵγ (%) 63 69ϵe+ (%) 30 70 ± 10Rµ+ (s−1) 3 × 107 7 × 107

Sensitivity (90% C.L.) 5.3 × 10−13 6 × 10−14

a) u vw

B

µ+ → e+γ [6]

(g − 2)µ[7] LHC

Belle II (g − 2)µ MEG II

2MEG PSI πE5PSI 1.3 MW 590 MeV

RF 50.63 MHzπE5

1 × 108 µ+/sMEG 3 × 107 µ+/s

MEG IIµ+ → e+γ

MEG

7× 107 µ+/s MEG IIMEG MEG II

1

MEG

MEG II

29.8 MeV/c

MEG 205 µm

140 µmMEG

21◦ 15◦

BC-400B

CCD

MEG II

MEG µ+ → e+γMEG II

22017

1PSI 5

2

3

2: 2017

CCD

2017100 µm

PSI

1.4 MW1.8 MW 2018–2019

30%–60%MEG II [8] MEG

II

HiMB[9]

3

100 MHz 2µ+ → e+γ

MEG II MEG

•

•

•

MEG COnstant Bending RAdius, CO-BRA 3

2

3

MEG

30%MEG II

∼90%

3.1 CDCH

MEG[10] MEG II

Cylindrical Drift CHamber, CDCH

MEG II CDCH50 MeV/c

50 µm 50 MeV/c5 mrad (RMS) MEG II

MEGII

MEG II CDCH 191 cm 17–29 cm

He : i-C4H10 = 90 : 1013056 1920

86.6–9.0 mm

106◦–8.5◦

µ+ → e+γ

2π2π

128030 kHz/cm2

3

4

3: CDCH

12 /cm2

PCB[11] 20 µm

4050 µm

20–30 gCDCH

2 mm

20 µm

CDCH 1.6 × 10−3 X0MEG 2.0× 10−3 X0

CDCH

KLOE [12]KLOE 80 µm

KLOE10

(INFNLecce) (INFNPisa) 2016

317

2017 7 660

20%2017 10

201810 9

3

PSI2018 7

10%

9

3.2 pTC

pixelatedTiming Counter, pTC pTC

MEG 75 ps(RMS)

MEG 30 ps

O(10 ps)

MEG30 ps

MEG40 ps

75 ps10 ps

4

5

4: MEG II pTC

1/√

N

4 pTC

256 9

MEG 2000SiPM

SiPM > 40%< 100 ps

SiPM

[13]5

BC-422 AdvanSiDSiPM 6 6 SiPM

7 m50 Ω

5: pTC4 cm 5 cm

ESR2

AdvanSiD SiPMSiPM

SiPM pTC

40%

pTC 2015 MEG II

1/4 128

SiPM

6

2015

2017512

4900 ℓ

Xe Xe

5

6

6: Xe

NaI 75%∼45 ns X0 = 2.77 cm

MEG MEG IIXe [14]

PMTMPPC4

6 MEG MEG II Xe2 PMT

216 12 mm MPPC 4092MPPC

MEG PMTPMT PMT

MEG II

21

MPPCMPPC 7 Xe

170 nm12 mm

MPPC

MPPC15%

12 mm 6 mmMPPC

4 SiPM MPPC

7: Xe PMT MPPC

8: MPPC Xe

5

∼30 nsMPPC

MPPC8 PCB MPPC

PCB

Xe 170 KXe

MPPC 4092 PMT 668Xe

8 PCB

MPPC2 ℓ Xe

2015 600 MPPC Xe

MPPC 2015 4 10

I-V

5

6

7

0.2% PCB

4 mXe

Xe PMTMPPC

Xe MEG5

XeMEG

PSI SCS

GM

GM

XeGM KEK LAr

MEG II

Xe

Xe

LEDMPPC

170 K Xe 3 t XeMPPC

1 m 1.6 mm

MEG II MPPC FAROXe

57Co X Xe

9:

MPPCMPPC

X FARO

300 µm2017

52.8 MeV9

1/4

45 ps

201773Li(p, γ)84Be 17.7 MeV

π−p → π0n π0 back-to-back55 MeV

5 RDCRDC (Radiative Decay Counter) MEG II

RDC RadiativeDecay, µ+ → e+νeν̄µγ

µ+ → e+γ

7

8

10: RDC

Eγ > 48 MeV 2:1

1–5 MeV

10 cm90%

COBRA

RDC12 2 cm LYSO 76

10Xe

LYSO

LYSO MPPCMPPC

pTCMPPC

100 ps LYSO1 MPPC LYSO

176Lu

11: XeRDC

2 kHz

2017 Xe11

Xe RDC

MPPC

250 µm

RDC

2 p.e.[15]

MEG II RDC15%

10%

8

9

12: WaveDREAM 16

6MEG II MEG

3 ∼900010

MEGMEG

II WaveDREAM PSI12

WaveDREAMSiPM

0.5–100

HV±2.5 V

MEG DRS (DominoRing Sampler) PSI

Switched Capacitor Array5 GHz 12 bit

WaveDREAM DRS80 MHz ADCFPGA (Field-Programmable Gate Array)

DRS

µ+ → e+γback-to-back

MEG II MPPCXe

10 Hz

0 20 40 60 80 100

weeks

14−10

13−10

12−10

)γ

e→

µB

R(

90% C.L. MEG Final

MEG II in 3 years

Discoveryσ5

Discoveryσ3

90% C.L. Exclusion

13: MEG II

WaveDREAM

130

72018 CDCH

2018CDCH

2019

13 MEG II

RDC

MEG MEGµ+ → e+γ20

6 × 10−14

9

10

MEXT/JSPS JP26000004JP17K14267 JP18K13557

[1] A.M. Baldini et al. (MEG Collaboration), Eur. Phys.J. C 76:434 (2016).

[2] , 36-3, 127 (2017).

[3] A.M. Baldini et al., Research proposal to PSI R-99-05.2 (2013), arXiv:1301.7225.

[4] A.M. Baldini et al. (MEG II Collaboration), Eur.Phys. J. C (in press), arXiv:1801.04688.

[5] L. Calibbi, G. Signorelli, Riv. Nuovo Cim. 41, 71(2018).

[6] A. Crivellin et al., Phys. Rev. D 97, 015019 (2018).

[7] M. Lindner et al., Phys. Rep. 731, 1 (2018).

[8] F. Berg et al., Phys. Rev. Accel. Beams 19, 024701(2016).

[9] A. Knecht, NuFact2017 (2017).

[10] , 27-4, 262 (2009).

[11] G. Chiarello et al., Nucl. Instr. Meth. A 824, 512(2016).

[12] M. Adinolfi et al., Nucl. Instr. Meth. A 488, 51 (2002).

[13] P.W. Cattaneo et al., IEEE Trans. Nucl. Sci. 61, 2657(2014).

[14] , 26-1, 9 (2007).

[15] Yu.M. Protopopov, V.G. Vasil’chenko Nucl. Instr.Meth. B 95, 496 (1995) .

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