In Radiative Muon Decay

荷電レプトンのレプトンフレイバー保存は破れているか？

大阪大学大学院理学研究科物理学専攻久野良孝

平成21年6月11日富山大学にて

!" Outline

• Intensity Frontier and Charged Lepton Flavor Violation (cLFV) • cLFV Physics Motivation with Muons • Overview of cLFV Experiments with Muons • μ→eγ • μ-e conversion • Experimental searches for μ-e conversion • cLFV of taus with neutrinos (if a time allows) • Summary

トラペは英語です、すみません。 !" Intensity Frontier and Charged Lepton Flavor Violation (cLFV)

!" From “Quantum Universe” The Big Questions to explore the mysteries of the Universe

DOE/NSF high energy physics advisory panel From “Quantum Universe” The Big Questions to explore the mysteries of the Universe

1. What is the origin of mass for fundamental particles? 2. Are there undiscovered principles of nature? 3. Are there extra dimensions of space? 4. Do all the forces becomes one? 5. Why are there so many kinds of particles? 6. What happened to the antimatter? 7. What is dark matter? How can we make it in the laboratory? 8. How can we solve the mystery of dark energy? 9. How did the universe come to be? 10. What are neutrinos telling us? The Standard Model continues working well, but DOE/NSF high cannot answer these fundamental questions. energy physics advisory panel Search for new physics at higher energy scale! Electroweak Epoch time energy scale scale Higgs particles

Supersymmetry

Uniﬁcation Epoch 13 10-9GeV 10 sec Grand uniﬁcation of fundamental forces 102sec 10-3GeV Origin of Neutrino mass (RH neutrino) 10-10sec 102GeV Leptogenesis (baryogenesis) 10-34sec 1016GeV

Quantum Gravity Epoch

1019GeV Superstrings Electroweak Epoch time energy scale scale Higgs particles

Supersymmetry

Uniﬁcation Epoch 13 10-9GeV 10 sec Grand uniﬁcation of fundamental forces 102sec 10-3GeV Origin of Neutrino mass (RH neutrino) 10-10sec 102GeV Leptogenesis Accelerators cannot (baryogenesis) 10-34sec 1016GeV reach directly here.

Quantum Gravity Epoch

1019GeV Superstrings Tools : The Three Frontiers of Particle Physics

Energy Frontier use high-energy colliders to discover new particles and directly probe the properties of nature

Intensity Frontier Cosmic Frontier use intense beams to observe reveal the natures of dark rare processes and study the matter and dark energy and particle properties to probe probe the architecture of the physics beyond the SM. universe.

from C. Baltay’s talk at the P5 meeting, 29 May 2008 The Intensity Frontier

• The Intensity Frontier is • an indirect search, but • energy scale that could be studied would be much higher than that of accelerators of O(1 TeV). • Through quantum radiative corrections • renormalization group equations usefulness of renormalization equations Quantum Corrections

• Effects are small. • High precision measurements • High intensity beams Which Rare Processes at Low Energy ?

• Processes which are forbidden or highly suppressed in the Standard Model would be the best ones to search for new physics beyond the Standard Model. • Flavor Changing Neutral Current Process (FCNC) • FCNC in the quark sector • b→sγ, K→πνν, etc. • Allowed in the Standard Model. • Need to study deviations from the SM predictions. • Uncertainty of more than a few % (from QCD) exists. • FCNC in the lepton sector • μ→eγ, μ+N→e+N, etc. ( Lepton Flavor Violation = LFV) • Not allowed in the Standard Model (~10-50 with neutrino mixing) • Need to study deviations from none • clear signature and high sensitivity neutrino factory Why Muons, not Taus ?

• Taus at B factories is not large enough, like about 10 taus/sec. • At future super-B factories, intensity increase of O(10-100) is expected. Also some of the decay modes are already background-limited. • Muons at PSI is about 108 /sec. • Intensity increase of 1011-1014 /sec with the technology developed for the front end R&D of muon colliders and/or neutrino factories, where intensity improvement factor of up to about O(1,000,000).

A larger window for new physics ! muon collider Physics Motivation of cLFV

!" Lepton Flavor Violation of Charged Leptons (cLFV)

LFV of neutrinos is conﬁrmed.

荷電レプトン混合現象LFV of charged leptons is not observed. LFV diagram in SUSY-GUT large top Yukawa coupling mixing µ˜ e˜ Standard Model Contribution from Neutrino Mixing (GIM µmechanism) e B˜ 2 2 3α mνl B(µ eγ)= (VMNS)µ∗ l (VMNS)el 2 LFV→ diagram 32in πStandard Model MW m! ixil ng in massive neutrinos ! !" ! ! 4 ! ∝ (m / m ) O(10ν -54W) mixing ≈ 10−26 νµ νe µ e W

A Large Window for New Physics beyond the Standard Model Various Models Predict Charged Lepton Mixing. ! anomaly in muon g-2 (?)

Hagiwara et al: hep-ph/0611102

Features •The decay rate is not too LFV in SUSY Models small, because it is determined by the SUSY mass scale. ! anomaly in muon g-2 (?) an+ example+ diagram → But, it contains the µ µ eγ e γ ˜ γ • → W information at 1016 GeV through the slepton mixing. Hagiwaraµ et al: hep-ph/0611102 e •It is in contract to proton decays or double beta ν˜µ ν˜e decays which need many Slepton Mixing particles.

Through quantum corrections, LFV νR could access ultra-heavy particles such as νR ν˜µ ν˜e (~1012-1014 GeV/c2) and GUT that cannot be produced directly by any accelerators. 6 H˜ SUSY GUT and SUSY Seesaw

The LFV search can study the physics here even if we can not directly produce the heavy particle ( ) at LHC

6 m2 m2 m2 Slepton Mixing 11 12 13 m2 = m2 m2 m2 ˜l 21 22 23 in mSUGRA Models ! 2 2 2 " m31m32m33

@ M_planck

GUT Yukawa interaction Neutrino Yukawa interaction

SUSY-GUT SUSY Seesaw Models Models

m2 A2 M m2 A2 M m2 ∼ 3 0 + 0 h2V V GUT m2 ∼ 3 0 + 0 h2 U U GUT ( L˜ )21 π2 t td tsln M ( L˜ )21 2 τ 31 32 8 Rs 8π MRs

CKM matrix Neutrino oscillation SUSY Predictions for cLFV

MEG

mu2e, COMET,super-MEG

PRISM MEG

mu2e, COMET,super-MEG

PRISM

SU(5) SUSY GUT SUSY Seesaw Model 10!8 Focus Point "#>µ$ µ#>e$, s =0.2 Complementarity 13 Tan%=50, µ<0, A =0 µ#>e$, s =0.05 !9 0 13 µ#>e$, s =0.02 10 13 µ#>e$, s =0.012 to LHC (mSUGRA) 13 10!10

Current Exp. Bound on µ#>e$ 10!11

• In mSUGRA, some of the 10!12

parameter regions, where LHC Branching Ratios !13 10 LHC does not have sensitivity to reach !14 Maximal Projected Exp. Bound on µ#>e$ SUSY, can be explored by cLFV. 10 10!15 • Bench mark points 0 500 1000 1500 2000 2500 3000

m! (GeV)

• Focus point !10 10

Current Exp. Bound on µ#>e$ • LHC can not cover and Figure 10: BR(τ µγ)and BR(µ eγ), for various values of s13 =0.2, 0.05, 0.02 → → and 0.012, along the extreme focus point region, in the (M1/2,m0) plane for tan β = 50, cLFV can cover. Excluded µ<0 and A0!12=0. Again, the parameter space points we use here are those such that 10 2 the higgsino content of the lightest neutralino is maximal. We show neutralinoby %h masses up to 3 TeV, which are still allowed by relic density considerations. The expected sensitivity of CERN LHC is showed by the vertical orange dotted line, while the yellow shaded area Maximal Projected Exp. Bound on µ#>e$ on the left indicates10!14 the bound stemming from the chargino mass limit set by LEP direct cLFV is complementary tosearches.

LHC, and in some case Branching Ratios 10!16

"#>µ$ has much better e , s =0.2 µ#> $ 13

µ#>e$, s13=0.05

µ#>e$, s13=0.02 Focus Point µ#>e$, s =0.012 13 Tan&=10, µ>0, A =0 sensitivity than LHC. 10!18 0 200 400 600 800 1000 1200 1400 1600 1800

m! (GeV)

Figure 9: BR(τ µγ)and BR(µ eγ), for various values of s13 =0.2, 0.05, 0.02 and → → 21 0.012, along the extreme focus point region, in the (M1/2,m0) plane for tan β = 50, µ<0 and A0 =0. The parameter space points we use here are those such that the higgsino content of the lightest neutralino is maximal. The cyan shaded region at large neutralino 2 masses gives an Ωχ˜1 h exceeding the current WMAP constraint on CDM density. We also show the current and projected sensitivities to BR(µ eγ). The CERN LHC reach lies → at neutralino masses smaller than 200 GeV. All the SUSY parameter space points in this plot are therefore outside CERN LHC reach at an integrated luminosity 100 fb−1. ∼

19 Short Summary of Physics Motivation : cLFV, Energy Frontier and SUSY

• In SUSY models, cLFV is • Slepton mixing is sensitive to sensitive to slepton mixing. either (or both) Grand Uniﬁed • LHC would have potentials Theories (SUSY-GUT to see SUSY particles. models) or neutrino seesaw However, at LHC nor even mechanism (SUSY-Seesaw ILC, slepton mixing would be models). difﬁcult to study in such a • If cLFV sensitivity is high precision as proposed extremely high, it might be here. able to explore multi-TeV SUSY which LHC cannot reach, in particular SUSY parameters. LFV Experiments

!" µ → eγ -2 cLFV History 10 µ → eee µA→eA 10-4 First cLFV search 0 KL → µe Ratio K+ → πµe 10-6 Branching

-8 of 10

Pontecorvo in 1947 limits -10 10 Upper

10-12

10-14

1940 1950 1960 1970 1980 1990 2000

Y e a r Present Limits and Expectations in Future

process present limit future µ→eγ <1.2 x 10-11 <10-13 MEG at PSI µ→eee <1.0 x 10-12 <10-13 - 10-14 ? µN→eN (in Al) none <10-16 Mu2e / COMET µN→eN (in Ti) <4.3 x 10-12 <10-18 PRISM τ→eγ <1.1 x 10-7 <10-9 - 10-10 super B factory τ→eee <3.6 x 10-8 <10-9 - 10-10 super B factory τ→µγ <4.5 x 10-8 <10-9 - 10-10 super B factory τ→µµµ <3.2 x 10-8 <10-9 - 10-10 super B factory List of cLFV Processes with Muons

ΔL=1 •µ+ → e+γ •µ+ → e+e+e− •µ− + N(A, Z) → e− + N(A, Z) •µ− + N(A, Z) → e+ + N(A, Z − 2)

ΔL=2 •µ+e− → µ−e+ •µ− + N(A, Z) → µ+ + N(A, Z − 2) + •νµ + N(A, Z) → µ + N(A, Z − 1) + + − •νµ + N(A, Z) → µ µ µ + N(A, Z − 1) eγ y ? µ→,Wh LFV What is μ→eγ ?

• Event Signature • Backgrounds • Ee = mμ/2, Eγ = mμ/2 • prompt physics (=52.8 MeV) backgrounds • angle θμe=180 degrees • radiative muon decay (back-to-back) μ→eννγ when two • time coincidence neutrinos carry very small energies. + e • accidental backgrounds • positron in μ→eνν • photon in μ→eννγ or µ photon from e+e- annihilation in ﬂight. γ MEG at PSI

• DC beam 107 muons/sec. • Goal : B < 2 x 10-13 • COBRA : spectrometer for e+ detection. • Liquid Xenon detector for photon detection.

P-Odd Angular Distribution of Polarized μ→eγ Decay (after its observation)

Left handed e+ Right handed e+ e+ 1 γ 2 1 1-cosϑ 1+cosϑe e 1 1 µ 2 µ 2

1 P-odd asymmetry 1 2 γ e+ reﬂects whether right or left- useful to distinguish different theoretical models handed slepton SU(5) SUSY-GUT non-unified SUSY with heavy neutrino have ﬂavor mixing, Left-right symmetric model Discriminate theoretical models SO(10) SUSY-GUT

Y.Kuno and Y. Okada, Physical Review Letters 77 (1996) 434 Y.Kuno, A. Maki and Y. Okada, Physical Reviews D55 (1997) R2517-2520 surface muons Suppression of Physics Background with Polarized μ→eγ Decay radiative muon decay at end-point of spectrum when neutrinos have small energy Angular distribution of integrate the decay width 1−δx < x < 1 δx : e energy 1−δy < y < 1 δy : γ energy Physics Background with 0 < z <δz δz : angle polarized muon decays α dB = J (1− P cosθ ) + J (1 + P cosθ ) 16π [ 1 µ eγ 2 µ eγ ]

1 + 1 γ e 2

J1 1 J2 1 µ 2 µ 2 J (νν ) = 1 JZ (νν ) = 0 Z

+ 1 γ 1 e 2 8 J = (δx)4 (δy)2 J = (δx)3(δy)3 1 2 3 if (δy) > (δx), then J 2 > J 1 , following a (1+Pµ cosϑ) Y. Kuno and Y. Okada, Phys. Rev. Lett. Improve a S/B ratio for µ+→ eRγ 77 (1996) 434 Suppression of Accidental Background with Polarized μ→eγ Decay

accidental coincidence between 52.8 MeV e+ and 52.8 MeV photon. In a high-intensity beam, it becomes more serious.

e+ in normal muon decay γ in radiative muon decay

e + γ 52 MeV 52 MeV

1+cosϑe 1+cosϑγ µ µ

suppressed if e+ going suppressed if photons going opposite to muon spin is opposite to muon spin is measured measured. 1 ∫ d(cosθ)(1+ Pµ cosθ)(1− Pµ cosθ) cosθ D + + + + η = 1 µ → eL γ µ → eL γ ∫ d(cosθD ) cosθ D

Both helicities are OK ! 2 1 2 = (1− Pµ ) + Pµ (1−cosθD )(2 + cosθ D ) Y. Kuno, A. Maki, and Y. Okada, Phys. Rev. D55 (1997) R2517 3

€ e conversion y ? µ→ ,Whin LFVa muonic atom What is a Muon to Electron Conversion ?

1s state in a muonic atom Neutrino-less muon nuclear capture (=μ-e conversion) nucleus µ − + (A, Z) → e− + (A, Z) µ−

lepton flavors muon decay in orbit changes by one unit. µ − → e−νν nuclear muon capture − − − − Γ(µ N → e N) − B(µ N → e N) = − ' µ + (A, Z) → νµ + (A, Z −1) Γ(µ N → νN ) μ-e Conversion Signal and Backgrounds

− − • The ratio of excited states µ + (A, Z) → e + (A, Z) versus the ground state is about 1:9 for Ti. • Signal • single mono-energetic electron m B 105MeV µ − µ ∼ • The transition to the ground state is a coherent process, and enhanced by a number of neuclus. Z5 ∝ Backgrounds

Category Examples of backgrounds

muon decay in orbit (DIO) Intrinsic Physics particle emissions from nuclear muon capture Backgrounds radiative muon capture (RMC)

radiative pion capture (RPC) Beam-related muon decay in ﬂight backgrounds neutrons, kaons, and anti-protons

cosmic rays Other Backgrounds miss-tracking events ExpectedExpected backgroundbackground sourcesource -- MuonMuon DecayDecay inin OrbitOrbit -- Muon Decay In Orbit (DIO) in a Muonic Atom 5 Muon decay in orbit (!(Eµe-Ee) )

! Ee > 103.9• MeVNormal muon decay has an endpoint of 52.8 MeV, whereas ! E = 350 keV !"#$#%&'()*)& " e the end point of muon decay in -18 ! NBG ~ 0.05 @orbit R=10 comes to the signal region. Background Rate•good resolutioncomment of electron Muon decay in orbit energy0.05 energy (momentum) reso 350keV(FWHM) is needed. Radiative muon capture 0.01 end point energy for Ti=89.7MeV Radiative pion capture 0.03 long flight length in FFAG, 2 kicker 5 Pion decay in flight 0.008 long flight(∆ lengthE) in FFAG, 2 kicker Beam electron negligible kinematically∝ not allowed 10-16 goal Muon decay in flight negligible kinematically not allowed +,-.'/01( Antiproton negligible absorber at FFAG entrance Cosmic-ray < 10^-7 events low duty factor $)/%1( -18 Total 0.10 10 goal 234+,'/01( • reduce the detector hit rate Instantaneous rate : 1010muon/pulse • precise measurement of the electron energy

2003/6/6 NuFact03@Colombia University μ-e Conversion : Target dependence (discriminating effective interaction)

2.5 dipole scalar 2 vector

" Z= $%# 1.5 N ! eN

! B

" Z # / 1 Better matching of muon N ! eN

! B w.f. and nucleus size 0.5 normalized at Al

0 0 10 20 30 40 50 60 70 80 90 100 Z

R. Kitano, M. Koike and Y. Okada, Phys. Rev. D66, 096002 (2002) Physics Sensitivity Comparison between μ→eγ and μ-e Conversion

Photonic (dipole) and non-photonic

contributions " (TeV)

48 -18 photonic non- B(!# e conv in Ti)"10 (dipole) photonic

4 yes 10 B(!# e conv in 48Ti)"10-16 μ→eγ no (on-shell)

μ-e yes -14 yes B(!# e$)"10 conversion (off-shell) B(!# e$)"10-13

10 3 more sensitive to new physics EXCLUDED -2 -1 2 10 10 1 10 10 ! SUSY Higgs Mediated Contribution (large tanβ)

R. Kitano, M. Koike, S. Komine and Y. Okada, Phys. Lett. B575, 300 (2003)

101

14 MN = 10 GeV tan$ = 60 100 )

# e "

µ B(µN eN) µ > 0 1 !1 → 10 µ < 0 A l ) / B (

B(µ eγ) 100 e → ∼ A l "

B ( !2 m0=M 10 1/2=2000 GeV m m B(µN eN) 0 =M 0=M 1/2 = 1/2=10 → O(1) 500 G 00 G !3 eV eV B(µ eγ) ∼ 10 → 200 400 600 800 1000 1200 1400

mH0 (GeV) Experimental Comparison between μ→eγ and μ-e Conversion

background challenge beam intensity • μ→eγ accidentals detector resolution limited • μ-e conversion beam beam background no limitation

• μ→eγ : Accidental background is given by (rate)2. The detector resolutions have to be improved, but they (in particular, photon) would be hard to go beyond MEG from present technology. The ultimate sensitivity would be about 10-14 (with about 108/sec) unless the detector resolution is radically improved. • μ-e conversion : Improvement of a muon beam can be possible, both in purity (no pions) and in intensity (thanks to muon collider R&D). A higher beam intensity can be taken because of no accidentals. μ-e conversion might be a next step. Experimental Design for Muon to Electron Conversion

!" Previous Measurements

PublishedSINDR Results (2004)UM II SINDRUM-II (PSI) 13 B(µ− + Au e− + Au)@< 7 PSI10− → × A exit beam solenoid F inner drift chamber 1m B gold target G outer drift chamber C vacuum wall H superconducting coil Class 1 events: prompt forward removed D scintillator hodoscope I helium bath J E Cerenkov hodoscope J magnet yoke - I e measurement H 3 SINDRUM II 10 e+ measurement G F D MIO simulation H D C E 10 2 @ PSI A µe simulation B

10 Final result on mu - e Class 1 events: prompt forward removed conversion on Gold e- measurement 1 3 target is being prepared + SINDRUM II

10 configuration 2000 e measurement 80 90 100 events / channel for publication MIO simulation Class 2 events: prompt forward 2 7-8 10 PSI muon beam intensity ~ 10 /sec µe simulation beam from the PSI cyclotron. To eliminate 10 10 Final result on mu - e -13 beam related background from a beam, a 1 < 7 x 10 90%CL beam vetocon counterversion was placed.on Gold But, it 1 could not work at a high rate. 80 90 100 target is being prepared momentum (MeV/c) 80 90 100 events / channel Class 2 events: prompt forward for publication

10 -13 1 < 7 x 10 90%CL

80 90 100 momentum (MeV/c) Improvements for Signal Sensitivity

To achieve a single sensitivity of 10-16, we need 11 10 muons/sec (with 107 sec running) whereas the current highest intensity is 108/sec at PSI.

Guide !’s until decay to !’s

Pion Capture and Muon Transport by Suppress high"P particles •!’s : p!< 75 MeV/c Superconducting •e’s : pe < 100 MeV/c Solenoid System Improvements for Background Rejection

Beam-related Beam pulsing with measured between beam backgrounds separation of 1μsec pulses

Muon DIO low-mass trackers in improve electron energy background vacuum & thin target resolution

Muon DIF curved solenoids for eliminate energetic muons background momentum selection (>75 MeV/c)

base on the MELC proposal at Moscow Meson Factory Mu2E at Fermilab

• After Tevatron shutdown, use the !"#$%&'($#)*#+,-#./Mu2E at Fermilab antiproton 0/+12$!+134#+

accumulator ring %98.$0/8**,.: and debuncher !1+:#/ ring for beam 09*#+38.<93/,.: %98.$;#1- !+1.6*8+/$087#.8,< 0/8* pulsing. >C@?$!$B$C@F$!D '+56/17 • Proton beam '178+,-#/#+

power is 20 kW 09*#+38.<93/,.: 09*#+38.<93/,.: E#/#3/8+$087#.8,< and 200 kW for =+8<93/,8.$087#.8,< >C@A$!$B$F@A$!D >?@A$!$B$C@?$!D '877,-1/8+6 pre and post Aim for 10-16

Project-X. Construction funding ~2005 Start physics run ~2010 After the cancellation of the MECO experimentCANCELLED in 2005 COMET (COherent Muon to Electron Transition) − − − in Japan B(µ + Al → e + Al) < 10 16

Proton Beam

Production The Muon Source Target •Proton Target •Pion Capture •Muon Transport

The Detector •Muon Stopping Target Stopping Target •Electron Transport •Electron Detection

proposed to J-PARC Design Difference Between Mu2e and COMET

Mu2e COMET

Muon Beam-line S-shape C-shape

Electron Straight Curved Spectrometer solenoid solenoid Muon Transport Solenoid Beam-line for COMET

• C-shape beam line : • better beam momentum separation • collimators can be placed anywhere. straight solenoid • Radius of curvature is can be inserted. about 3 meters. • A straight solenoid section can be inserted between the two toroids. • Reference momentum is 35 MeV/c for 1st bend and 47 MeV/c for 2nd bend. Curved Solenoid Spectrometer for COMET

• 180 degree curved • Bore radius : 50 cm • Magnetic ﬁeld : 1T • Bending angle : 180 degrees • reference momentum ~ 104 MeV/c • elimination of particles less than 80 MeV/c for rate issues • a straight solenoid where detectors are placed follows the curved spectrometer. schematic 60!MeV/c DIO electrons 1 s p2 + 1 p2 D[m] = l 2 t 0.3 B[T ] × R × p × l

Event Displays for Curved Solenoid Spectrometer

Transmission Efficiency 0.4

105!MeV/c !!e electron 0.35

0.3

0.25

Transmission Efficiency 0.2

0.15

0.1

60!MeV/c0.05 DIO electrons

0 2 1 2 0 20 40 60 80 100 1 s pl + 2 pt Electron Total EnergyD (MeV)[m] = 0.3 B[T ] × R × p × l

Transmission Efficiency 0.4

105!MeV/c !!e electron 0.35

0.3

0.25

Transmission Efficiency 0.2

0.15

0.1

0.05

0 0 20 40 60 80 100 Electron Total Energy (MeV) J-PARC at Tokai, Japan 93

7&8%(-9234#%+0#-'&$ :&'#%+&$;<+=#9>"+#-"# 5&"+$+'6 5&"+$+'6

!""#$ !""#$#%&'(%)*%+,#- .%&-/01'&'+(- 234#%+0#-'&$ 5&"+$+'6

D#1'%+-(95&"+$+'6

<+-&" @E#F9>6-"H%('%(- ABE#FG>6-"H%('%(- ?@AB0C IMA7NOP:LQ IBJKA:LC Signal Sensitivity (preliminary) - 1 SSC years

• Single event sensitivity

− − 1 B(µ + Al → e + Al) ∼ , Nµ · fcap · Ae

• Nμ is a number of stopping muons in the muon stopping total protons 4x1020 target. It is 1.1x1018 muons. muon transport efﬁciency 0.009 • fcap is a fraction of muon muon stopping efﬁciency 0.3 capture, which is 0.6 for # of stopped muons 1.1x1018 aluminum. • Ae is the detector acceptance, which is 0.04.

17 B(µ− + Al e− + Al) = 3.3 10− → × 17 B(µ− + Al e− + Al) < 7 10− (90%C.L.) → × BG with asterisk needs beam extinction. Background Rejection Summary (preliminary)

Backgrounds Events Comments Muon decay in orbit 0.05 230 keV resolution Radiative muon capture <0.001 (1) Muon capture with neutron emission <0.001 Muon capture with charged particle emission <0.001 Radiative pion capture* 0.12 prompt Radiative pion capture 0.002 late arriving pions Muon decay in ﬂight* <0.02 (2) Pion decay in ﬂight* <0.001 Beam electrons* 0.08 Neutron induced* 0.024 for high energy neutrons Antiproton induced 0.007 for 8 GeV protons Cosmic-ray induced 0.10 10-4 veto & 2x107sec run (3) Pattern recognition errors <0.001 Total 0.4 10-18 Sensitivity with PRISM

!" Further Background Rejection to < 10-18

Pion long muon beam-line muon storage background ring

Muon DIO narrow muon beam 1/10 thickness muon stopping background spread target

Beam-related Extinction at muon fast kickers Background beam

Cosmic-ray low-duty running 100 Hz rather background than 1 MHz PRISM=Phase Rotated Intense Slow Muon source PRISM Muon Beam

Capture Solenoid muon intensity: 1011~1012 /sec central momentum: 68 MeV/c narrow momentum width by phase rotation Matching Section pion contamination : 10-20 for 150m Solenoid

Ejection System Injection System

C-shaped FFAG Magnet

FFAG ring Detector RF Power Supply RF Cavity RF AMP Phase rotation = accelerate slow muons and decelerate fast muons by RF 5 m R&D on the PRISM Muon Storage (FFAG) Ring at Osaka University

PRISM-FFAG (6 sectors) in RCNP, Osaka

Ready to demo. phase rotation Research Center for Nuclear Physics (RCNP), Osaka University

阪大核物理研究センター西実験室Research Center for Nuclear Physics (RCNP),R&D Osaka案 University has a cyclotron of 400 MeV with 1 microA. The energy is above pion threshold.

Muon西実験室 Source with low proton power at Osaka U.? PRISM-FFAG R&D 阪大核物理研究センター西実験室R&D案 MUSIC (=MUon Science International Center)

muon yield estimation 50 kW : 1011 muons/sec (for COMET) 0.4 kW : 109 muons/sec (for MUSIC)

位相空間回転システム

FFAG電磁石

スパイオン崩壊ーペスミューオン輸送部システムミューオン蓄積FFAGリング用 m 験 3 実 x m 3

キッカー電磁石偏向電磁石ミューオン輸送ビーム・ライン系

ステアリング電磁石陽子ビーム軸

パイオン捕獲部システム

ビームダンプ搬入口 The pion capture system has been approved in the 2008 supplementary government budget. Long Future Prospects : From COMET to PRISM

COMET PRISM

Production Target

Stopping Target

− − − − − −18 B(µ + Al → e + Al) < 10 16 B(µ + Ti → e + Ti) < 10 •with a muon storage ring. •without a muon storage ring. •with a fast-extracted pulsed proton beam. •with a slowly-extracted pulsed proton beam. •need a new beam-line and experimental •doable at the J-PARC NP Hall. hall. •regarded as the ﬁrst phase / MECO type •regarded as the second phase. •Early realization •Ultimate search mSUGRA with right- µ<0,µ<0, handed neutrinos 10-11 -9 >µ>µ 10 µ > , 10-12 Current Exp. Bound on µ→e ; Ti (SINDRUM II) µ > -10 µ > 10 µ > 10-13

-11 ) 10 γ will be improved e e ; Ti) -14 → µ by a factor of → 10 (

µ -12

( 10 10,000. LHC reach 10-15 MEG (µ→eγ) 10-13 10-16 will be improved This Experiment ( e;Al 10-14 µ→ ) Branching Ratios Branching Ratios by a factor of 10-17 1000,000. 10-15 PRISM phase-2 10-18 10-16 10-19 0 0.5 1.0 1.5 2.0 2.5 3.0 mχ (TeV) − − − B(µ + Al → e + Al) < 10 16

Sensitivity Goal − − − B(µ + Ti → e + Ti) < 10 18 まとめ

• 荷電レプトンのレプトンフレーバー非保存探索実験（cLFV）の物理的意義は深い。 • ミューオンを使ったcLFV探索としては、例えばμ→eγ やミューオン電子転換過程 (μ-e conversion) などがある。後者は物理的にも実験的にもより重要である。 • μ→eγを探索するPSIでのMEG実験は 10-13 の実験精度を目指し、現在実験が進行中である。 • 将来の次世代の実験はミューオン電子転換過程 (μ-e conversion) である。現在、米国で10-16の実験感度を目指すフェルミ加速器研究所でのMu2E実験と日本のJ-PARC での COMET が計画されている。 • 更に、将来の拡張として、10-18 以下の実験感度を目指すPRISM/PRIMEの研究開発も大阪大学を中心として行われている。 • 理論的にも実験的にも支援をお願いします。。。。。 End of My Slides