1. μ-e Conversion Experiment with Pulsed Proton Beam ---DeeMe---
M. Aoki, Osaka University
on behalf of DeeMe working group
TRIUMF, Vancouver, 2010/4/28

3. DeeMe Collaboration JAERI KEK Osaka University TRIUMF UBC M. Kinsho
M. Ikegami, S. Mihara, K. Yoshimura, N. Saito, H. Iinuma, H. Nishiguchi, C. Ohmori, M. Yoshii, K. Shimomura, N. Kawamura, S. Patrick, K. Nishiyama, M. Yoshida
Osaka University
M. Aoki, A. Sato, T. Itahashi, Y. Kuno
TRIUMF
T. Numao, J. Doornbos
UBC
D. Bryman

4. Contents J-PARC Introduction Muon in Particle Physics
Charged Lepton Flavor Violation
mN→eN Process
Experiments Searching for mN→eN Process
Principle of experiment
A new idea
J-PARC
Test J-PARC MLF D2
DeeMe
Single Event Sensitivity
Background
Summary

5. Standard Model of Particle Physics
There are three generations (flavors) of Quarks and Leptons.
Muon was found at 1936.
I.I. Rabi said “Who ordered that?”
Is the muon excited state of electron?
The world-first search for muon rare process: m -> e
Null Result → a hint of generation
1958
But exp. already gave BRexp. < 2 x 10-5
→ Two neutrinos model
ne ≠ BNL
Toward the establishment of the concept of “generation/flavor”.
Muon played very important role in the development of particle physics.

6. Today, what do we know about generation (flavor)
Quark Mixing
Cabbibo-Kobayashi-Maskawa (CKM) Matrix
Established --- Novel
Neutrino Mixing
Pontecorvo-Maki-Nakagawa-Sakata (PMNS) Matrix
Homestake, Kamiokande, SNO, T2K etc.
Observed and Established.
Charged Lepton Flavor Violation (CLFV)
No observation yet at all.
Implemented to the Standard Model of Particle Physics as “forbidden”. s b d u c t
Quarks t e ne nm nt m ?
Leptons

7. Charged Lepton Flavor Violation
charged Lepton Flavor Violation (CLFV)
Forbidden in the SM
μ-+A→e-+A , μ→eγ, μ→eee, τ→e(μ)γ, τ→e(μ)h ...
Neutrino-mixing predicts very small amount of CLFV via higher order diagram; it is as small as practically impossible to observe in foreseeable future.
CLFV = Physics beyond SM with neutrino oscillation
A. de Gouvea 7

8. History of CLFV Searches
Since 1948
E.P. Hincks and B. Pontecorvo, PR 73 (1948) 257
m → e g: Concept of “Flavor”
History of CLFV = History of particle physics.
The best limits from muons.
Current Limits
m → e g: < 1.2 x (MEGA)
m-N → e-N: < 7x10-13(SINDRUM II)
On-going program
MEG/PSI m → e g: < 10-13
After Yoshitaka Kuno 8

9. SUSY and CLFV Standard Model ≠ “the theory of everything”.
Hierarchy Problem
Unification of Force
Supersymmetry (SUSY)
If SUSY exists → SUSY flavor mixing → CLFV 9

10. Golden Trio
g-2
EDM
m-LFV
Real
Imaginary
slepton mass matrix
τ-LFV

11. CLFV Predictions SUSY+Seesaw, MSW Large Angle tanβ=30 tanβ=10 tanβ=3
MEG
SUSY+Seesaw, MSW Large Angle
tanβ=3
tanβ=10
tanβ=30
DeeMe
L. Calibbi, A. Faccia, A. Masiero and S.K. Vempati PRD 74(2006)

12. m- + N → e- + N Muonic Atom (1S state) μ-e Conversion
MC:MDO = 1:1000(H), 3:2(Al), 13:1(Cu)
τ(free μ-) = 2.2 μs
τ(μ-;Al) = 0.88 μs
μ-e Conversion
Muon Capture(MC) μ−
nuclei
Muon Decay in Orbit (MDO)
charged Lepton Flavor Violation (CLFV) 13

13. Physics of μ-e Conversion
SUSY-GUT, SUSY-seesaw (Gauge Mediated process)
BR = = BR(μ→eγ) × O(α)
τ→lγ
SUSY-seesaw (Higgs Mediated process)
BR = 10-12~10-14
τ→lη
Doubly Charged Higgs Boson (LRS etc.)
Logarithmic enhancement in a loop diagram for μ-N → e-N, not for μ→e γ
M. Raidal and A. Santamaria, PLB 421 (1998) 250
SUSY with R-parity Violation
Leptquarks
Heavy Z’
Compositeness
Multi-Higgs Models N N

14. Principal of Experiment
SINDRUM II
Signal : μ- +(A,Z) → e- +(A,Z)
A single mono-energetic electron
105 MeV
Delayed：~1μS
No accidental backgrounds
Physics backgrounds
Muon Decay in Orbit (MDO)
Ee > MeV (BR:10-14)
Ee > MeV (BR:10-16)
Beam Pion Capture
π-+(A,Z) → (A,Z-1)* → γ+(A,Z-1) γ → e+ e-
Prompt timing
BR[Al] < 7 × 10-13 15

15. SINDRUM-II
PSI/πE5
SINDRUM II 16

16. SINDRUM II (2) Need more muonic atoms: >1010 μ-/s.
Beam-induced prompt backgrouds:
Pulsed beam.
Detector rate might be too high:
Some Ideas to reduce it.
BR < 7 × 10-13 17

17. CLFV and Related Programs
FNAL: BR(μ- N → e- N) < 10-16
FNAL: μ g-2 < 0.1 ppm
LHC: SUSY Search
Bs → μ+μ-, Bs → τμ, τ → μμμ
KEKB: τ → e(μ) γ, τ → e(μ) η ...
BR < 10-8
BNL: μ g-2 < 0.5 ppm
>3-σ off from SM
PSI/MEG: BR(μ → e γ) < 10-13
J-PARC: BR(μ- N → e- N) < , 10-16
J-PARC: μ g-2 < 0.1 ppm
PSI: μ EDM
J-PARC: μ EDM

18. General Idea of μ-e Conversion Setup
Sensitivity
High m- yield
Background
Pulsed Proton
Detector Rate
Momentum Selection before Detector

19. μ-e electrons may directly coming from a production target.
→ DeeMe
an electron analogue of the surface muon.
the same idea by Doug Bryman and Toshio Numao, independently
Experiment could be very simple, quick and low-cost.

20. Test Measurement How many m- actually stop in the muon target?
What is the potential source of backgrounds.
→ Test Measurement at J-PARC MLF, Tokai, Japan
Tokai, Japan

21. J-PARC LINAC RCS MR H-, 400 MeV, 50 mA 50 Hz 3 GeV, 333 μA 25 Hz
Vancouver
Tokai, Japan
LINAC
H-, 400 MeV, 50 mA
50 Hz
RCS
3 GeV, 333 μA
25 Hz
Fast Extraction
Material and Life-science Facility (MLF) MR
30 GeV, 15 μA
Fast and Slow EX

22. J-PARC MLF Muon Facility
3-GeV Proton

23. Test Measurement at D2 How many m- actually stop in the muon target?
What is the potential source of backgrounds.
Muonic Atom Formation Rate Measurement
Yield of Michel e- from target.
Decay constant of e-
e- from carbon: 2.0 msec
Otherwise, << 2.0 msec
Extinction Ratio Measurement
Time structure of high momentum e- (Ee- > 52 MeV)

24. D2 Beamline Geometrical Acceptance: 45--60 msr Momentum Bite: 3%r.m.s.
Beamline Length: ~40 m
Surface muon yield
~ kW protons

25. Detector for the Test Meas.
Pb (4mmt)
Plastic Scintillator
D2 Exit
B1: gating-PMT readout
B2: gating-PMT readout
B3: ND filter (1/1000), normal PMT readout μ- e- B1 B2 B3
Should detect delayed e- after prompt burst (>104/pulse)
Beam time approved is very short
→ Use gating-PMT to increase delayed-time detection efficiency.
Background e- coming from the decay of prompt m- stopped in counters.
→ Pb plate to absorb m- by muon capture process.
Electron-detection efficiency ~ 50%

26. gating PMT No. of particles in a prompt pulse ~1e5
Standard PMT is saturated.
Used a gating PMT system
off/on gain ratio = 1e6
Designed by Taniguchi

27. Snapshot of PMT signal B1
Plas. Scinti.
gating B2 B3
normal PMT
ND filtered
Baseline distortion due to delayed fluorescence from plastic scintillator.
Individual hits by real particles can be seen on the baseline.

28. Result Intrinsic Counter Efficiency:~100% τ=2.10±0.02 μsec
Potential contamination of e- from Bhabha scattering of e+ from m+ decay.
But only order 2 at most.
Existence of Michel Edge: confirmed
The shape of spectrum is consistent with that obtained with G4Beamline Simulation.
→ e- from Muonic Carbon Atom: Confirmed
Yield: 4.4 detector
= 450
B1 pulse height
(B2 tagged)
B2 pulse height
(B1 tagged)

29. G4Beamline Estimation G4Beamline model of D2 beam line 28 MeV/c μ-
Geometrical Acceptance:40 msr
Yield: 4.4 detector
→ 8 × 109 /sec/MW in the Muon Production Target.

30. Sensitivity w/ current D2
D2 and the current muon target
RμC = 8 × 109 sec/MW
D2 Acceptance: 105 MeV/c
Muon Capture Rate(Carbon) = 0.08
Time Window Acceptance = 66%
μ-e relative strength (normalized to Al) = 0.7
Running Time 107 sec
S.E.S. = 8 × [Al equivalent]
SINDRUM II limit = 7 × 10-13
Not impressive.
Do not worry. This is not an end of story.

31. Sensitivity w/ a new Beamline
Place Al μ-stopper: Capture rate 0.08 → 0.60
New Beam line with larger acceptance: x4
Exclusive use of the New Beam line: x2 or more
S.E.S < for Al π- μ-

32. Concept of the New BL
Concept by Jaap Dornbos (TRIUMF) Detailed Design is on-going.
Solenoid focusing + dipole for bend
The first Solenoid could be a single type.
Kicker to reduce prompt burst 1/1000
Spec: J-PARC RCS type is OK
Acceptance = 140 msr
Δp/p = 10 MeV/c(FWHM)
H line

33. Backgrounds How much difficult to achieve the extinction 10-14?
Should Delay by ~msec ** Only coming from μ decay.**
Background: Muon Decay in Orbit : mostly Ee < 55 MeV
NDIO < 10-14: Ee > MeV
Signal: μ-e Electron: Pe = 105 MeV/c
If there is any off-timing protons, that could become potential background.
Extinction < 10-14
Rextinction[COMET] < 10-9, Rπ-survive[COMET] = 10-5
How much difficult to achieve the extinction 10-14?
Fast Extraction
No scattering by septum during the slow extraction.
Fall time of kicker is very fast.
< 300 nsec.
There is a room to install additional kickers in the primary beam line.

34. DeeMe @ J-PARC MLF Sensitivity Schedule DeeMe <10-14 ~2015
new dedicated beamline
high-power pulsed proton beam
mu-e conversion
Sensitivity
Schedule
DeeMe
<10-14
~2015
COMET/Mu2E
<10-16
2017~

35. Summary
A new idea of m-e conversion experiment (DeeMe) that could improve the current limit by 2 orders of magnitudes (BR < 10-14) was shown.
Test Measurement at J-PARC MLF D2 was performed.
The time constant of e- from D2 is consistent with m- decay in carbon.
The shape of spectrum is consistent with Michel Spectrum.
The rate of muonic carbon atom formation is 8 × 109 Muon Target
Very good agreement with Geant4 MC: 7 × 109 /sec/MW
The extinction should be < 10-14, which would be a severe requirement. But,
Fast-extracted beam should have much better extinction than slow-extracted beam.
Extra Extinction Kicker (The same type as the current RCS kicker) can be located in the primary beam line.
Expression of Interest (EoI) is open to the public.
Working for the detailed design of experiment.
See for more information.