MEG. 2.1 KEK PSI PSI MEG II [4] GeV 2. Tevatron [5] 2017 ( 29 ) 12 12

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1 27 MEG µ + e + γ mori@icepp.s.u-tokyo.ac.jp 27 ( 29 ) 2 2 MEG Mu-E-Gamma [] 999 KEK PSI [2] PSI PSI µ eγ [3] MEG II [4] MEG 2 µ eγ µ eγ a µ eγ 54 µ eγ b µ eγ : a b µ eγ CERN LEP Z 6 GeV LEP 75 GeV Tevatron µ eγ 4 [5] µ eγ

2 2 28 µ eγ µ eγ [6] µ eγ [7] 996 PSI 997 µ eγ PSI 998 Letter of Intent [8] 999 [2] µ eγ O( 2 ) 22 LHC 25 GeV LHC 25 b LHC LHC µ eγ LHC 3: a µ µ eγ [] 2: LEP 6 GeV a µ = (29 ± 8) µ eγ 2 δ 2 LL = 4 3 µ 3e µn en µ eγ 2.2 LHC b a µ =(g µ 2)/2 26 a µ [9] 3.5σ µ eγ 3 a µ a µ B(µ eγ) [] µ + e + e e + µ 3e µ N e N N µ eγ α / B(µ + e + e e + ).6 B(µ + e + γ) R(µ Al e Al).26 B(µ + e + γ) R(µ N e N)

3 3 29 µ 3e µn en µ eγ 4 MEG µ 3e µn en 22 O( 4 ) µ eγ µ eγ µ 3e µn en µ eγ µ 3e µn en 4: µ eγ 9% µ 3e µn en µ eγ MEG II COMET-II/Mu2e Mu3e-III 4 µ eγ µ eγ 52.8 MeV MeV/c % µ eγ µ eγ 3 3 % 7 µ + e + ν ν µ eγ AIF: Annihilation in Flight µ eν νγ µ eγ 52.8 MeV % 5% 4 µ eγ 52.8 MeV

4 MeV MEG [] 5 5. PSI 7 8 PSI PSI 59 MeV ma.4 MW 5.6 MHz RF 2 µsec PSI 3. ma.8 MW 4 cm MEG πe5 66 BTS COBRA BTS COBRA 2.3 cmφ 25 µm 2 Rohacell /sec 2 3 5: MEG µ eγ 5 MEG µ eγ COBRA 3 7 COBRA COnstant Bending RAdius T.49 T 7 a COBRA

5 5 3 μ + e + (a) 6: COBRA 6 7 b COBRA COBRA.2X µ eγ 52.8 MeV 85% KEK COBRA COBRA 5 µsr 45 MeV/c DC DC TC 5 DC TC μ + e + (b) 7: COBRA a b DC 52.8 MeV AIF COBRA DC mm 2 2 COBRA khz Charge Division DC 2.5 µm 25 nm DC.5 Pa 52.8 MeV 2 3 X 52.8 MeV.58% σ 8

6 6 32 Number of events /(.25 MeV) Relative efficiency E e (MeV) 8: Number of events /(.8 nsec) N RMD = 37 ± 42 sigma = 23 ± 3 ps -2-2 (nsec) 9: t eγ 5.3 t eγ DC TC TC cm 3 TC COBRA cm TC TC TC DC TC 5 7 ps DC TC ps TC 9 22 ps Z 2 : MEG

7 cm NaI 75 % 45 nsec 8 l Radiative decay & e + annihilation Number of events /(.5 MeV) 5 2 (a) (b) w < 2 cm w > 2 cm Pileup Cosmic ray 2: (MeV) : 54.9 MeV a 2 cm b 2 cm 5 mm 5 MeV 65 7 psec E γ KEK COBRA C [2] µ eγ DRS: Domino Ring Sampler DRS

8 8 34 Energy scale (arb. unit) Xe 2 ppb 3m 2/ Timing Counter target LXe Detector Drift Chamber Muon Beam 4:.96 3/2 /9 / /7 3/8 3/ 3/8 3/ 3/2 2/ :.2% rms 7.6 MeV 2 π p π n MeV 82.9 MeV 54.9 MeV 52.8 MeV 54.9 MeV µ eγ b a.7 2.4% CW COBRA 7.6 MeV 3-4 CW MeV 3.2% rms 24 Am 9 MeV 6 µ + e + γ MEG 28 [3] 4 [3, 4] 29 [5] µ eγ Likelihood PDF

9 9 35 E γ (MeV) t eγ (nsec) events / 56 (ps) 45 (a) events /.24 (MeV) (b) events /.4 (MeV) 3 2 (c) (ns) t e + γ E e (MeV) E γ (MeV) E e (MeV) cosθ eγ 5: MEG µ eγ σ.64σ 2σ t eγ cos Θ eγ 9% cos Θ eγ < t eγ <.24 ns E γ 7% E e 9% 5. < E γ < 55.5 MeV 52.4 <E e < 55. MeV Θ eγ PDF 48 <E γ < 58 MeV t eγ < ns µ eγ Likelihood 4 5 MEG E γ, E e, t eγ, cos Θ eγ σ events / 2. (mrad) (mrad) e + γ (d) events / 3. (mrad) 4 (e) (mrad) e + γ events /.6 3 (f) R sig 6: a e Likelihood MEG f R sig 9% Likelihood 6 a e Likelihood 6 f R sig log (S/(f R R + f A A)) S R A PDF f R f A % CL : µ eγ 3 9% C.L. Profile Likelihood Ratio Frequentist Approach 9% µ eγ µ eγ 3.5%

10 MEG µ eγ % C.L. MEG ILC K CP 3 B µ eγ MEG II KEK MEG MEG [] [2] T. Mori et al., Research Proposal to PSI, R , May 999. [3] A.M. Baldini et al. (MEG Collaboration), Eur. Phys. J. C, 76:434, -3 (26). [4] A.M. Baldini et al. (MEG II Collaboration), arxiv: (23); MEG II Design Report. [5] R. Barbieri and L.J. Hall, Phys. Lett. B338 (994) 22; R. Barbieri, L.J. Hall, and A. Strumia, Nucl. Phys. B445 (995) 29. [6] J. Hisano and D. Nomura, Phys. Rev. D 59 (999) 65. [7] 2,, UT-ICEPP 96-2, April 996. [8] A.v.d.Schaaf et al., Letter of Intent for an experiment at PSI, R-98-5., May 998. LoI [9] G.W. Bennett et al., Phys. Rev. D 73 (26) 723. [] G. Isidori, F. Mesia, P. Paradisi, D. Temes, Phys. Rev. D 75 (27) 59. [] J. Adams et al. (MEG Collaboration), Eur. Phys. J. C, 73, 2365 (23). [2], 26-, 9 (27). [3], 28-4, 227 (2). [4] J. Adams et al. (MEG Collaboration), Nucl. Phys. B 834, -2 (2); Phys. Rev. Lett. 7, 78 (2); Phys. Rev. Lett., 28 (23). [5],, 29-3, 33 (2); R. Sawada, Proceedings of ICHEP2, Paris, France, PoS (ICHEP 2) PRL [4]