-
1
MEG II — 10−14 µ+→ e+γ —
[email protected] [email protected]
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) .
10