mN-eN Rare Process

M. Aoki, Osaka UniversityMuSAC-2009, Tokai, 2010/3/10-11

Contents• Introduction

– Muon in Particle Physics– Charged Lepton Flavor Violation– mN→eN Rare Process

• Experiment Searching for mN→eN Rare Process– Principle of experiment– COMET– A new idea

• Test Measurement @ MLF/D2• DeeMe

– Single Event Sensitivity– Background

• Summary

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 m -> e g

@1947– Null Result → hint of generation/flavor

• BRtheory(m->eg)~10-4 @ 1958– But exp. already gave BRexp. < 2 x 10-5

→ Two neutrinos model

• ne ≠ n m @1962 BNL– Toward the establishment of the

concept of “generation/flavor”.

3

Muon played very important role in the development of particle physics.

Flavor Mixing• Quark Mixing

– Cabbibo-Kobayashi-Maskawa (CKM) Matrix

– Established --- Novel Prize@2008• Neutrino Mixing

– Pontecorvo-Maki-Nakagawa-Sakata (PMNS) Matrix

– Homestake, Kamiokande, SNO etc.– Observed and Established.

• Charged Lepton Flavor Violation (CLFV)– Not observation yet at all.– Forbidden in the Standard Model of

Particle Physics. 4

s bd

u c t

te

ne nm

nt

m? ?

5

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 10-11 (MEGA)• m-N → e-N: < 7x10-13(SINDRUM II)

•On-going program•MEG/PSI → m e g: < 10-13

After Yoshitaka Kuno

• Standard Model ≠ “the theory of everything”.– Hierarchy Problem– Unification of Force

• Supersymmetry(SUSY)

• If SUSY exists→ SUSY flavor mixing→ CLFV

6

SUSY and CLFV

7

Theoretical PredictionsProcess Current

Limit

SUSY-GUT SUSY-

Seesaw Future

μ N → e N 10-13 10-14-10-

17

10-13-10-

15

10-14,10-

16,10-18

μ → e γ 10-11 10-14 10-13 10-13

τ → μ γ 10-6 10-9 10-8 10-8

PRISM

MEG

Courtesy Hisano

PRISM

MEG

SUSY+Seesaw, MSW Large Angle

SUSY-GUT

COMET COMET

tanβ=3

tanβ=10

tanβ=30

→ Physics at TeV scale, or even much higher energy domain.

m- + N → e- + N• Muonic Atom (1S state)

– 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

8

nucleiμ−

Muon Decay in Orbit (MDO)

charged Lepton Flavor Violation (CLFV)

Muon Capture(MC)

9

Principal of Experiment

• Signal : μ- +(A,Z) → e- +(A,Z)– A single mono-energetic electron• 100 MeV• Delayed ： ~1μS

• No accidental backgrounds• Physics backgrounds– Muon Decay in Orbit (MDO)• ΔEe=350 keV (BR:10-16)

– Beam Pion Capture• π-+(A,Z) → (A,Z-1)* → γ+(A,Z-1)

γ → e+ e-

• Prompt timing

SINDRUM II

BR[Al] < 7 × 10-13

General Idea of Setup

• Sensitivity– High m- yield

• Background– Pulsed Proton

COMET @ J-PARC/MR

COMET: BR[Al] < 10-16

12

μ-e electrons may directly coming from a production target.

an electron analogue of the surface muon.Experiment could be very simple, quick and low-cost.

Issues to be Checked

• 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)

• 2009A0023: 3 days• 2009A0032: 1 day

• How many m- actually stop in the muon target?• What is the potential source of backgrounds.

Detector for the Test Meas.

D2 Exit

Pb (4mmt) Plastic Scintillator

μ-

e-

B1B2 B3

• B1: gating-PMT readout• B2: gating-PMT readout• B3: ND filter (1/1000),

normal PMT readout

•Have to detect delayed e- after prompt burst (~104/pulse).•Beam time approved is very short

•→ Use gating-PMT to increase delayed-time efficiency.•Background e- coming from the decay of prompt m- stopped in counters.

•→ Pb plate to absorbe m- by muon capture process.•Electron-detection efficiency ~ 50%

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 counts/pulse/100-kW @ detector• → 8 × 109 /sec/MW in the current Muon Target.• Ne+/Ne-@40-MeV/c = 450

B1 pulse height(B2 tagged)

B2 pulse height(B1 tagged)

Sensitivity

π-

μ-

• D2 and the current muon target– RμC = 8 × 109 sec/MW– D2 Acceptance: 0.04% @ 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 × 10-13

• SINDRUM II limit = 7 × 10-13

• 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 < 10-14 for Al

New Beamline• Concept by Jaap Dornbos (TRIUMF)

Detailed Design is on-going.• Double Thin Solenoid to preserve

momentum-dispersive plane.• 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

Backgrounds• Should Delay by ~msec ** Only coming from μ decay.**– Background: Muon Decay in Orbit : mostly Ee < 55 MeV– NDIO < 10-14: Ee > 102.5 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.

DeeMe @ J-PARC MLF

mu-e conversion

Sensitivity Schedule

DeeMe <10-14 ~2015

COMET <10-16 2017~

DeeMe does not replace COMET.DeeMe and COMET are complementary.Sound scenario to secure the world-first discovery.

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.

• DeeMe will never replace COMET, but they are complementary.

– DeeMe → COMET

• Test Measurement at 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 /sec/MW @ Muon Target

– Very good agreement with Geant4 MC: 7 × 109 /sec/MW

• The extinction should be < 10-14, which is much severe than COMET. 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 beamline.

• Expression of Interest (EoI) is out.

• Working for the detailed design of experiment.