μ-e conversion 探索実験--- COMET ---

Masaharu Aoki, Osaka U.

「J-PARCハドロン物理の将来研究計画を考える」研究会理化学研究所

2008/9/1-2

内容• イントロダクション• μ-e conversion 探索実験 @J-PARC --- COMET

• パルス陽子• パイオン捕獲ソレノイド• カーブソレノイドスペクトロメータ• 実験感度

• mu2e@FNAL

• まとめ

3

• 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

nucleiµ−Muon Decay in Orbit (MDO)

Coherent Process

μ-e Conversion

Muon Capture(MC)

BR[µ! + (A,Z)! e! + (A,Z)] " ![µ! + (A,Z)! e! + (A,Z)]![µ! + (A,Z)! !µ + (A,Z # 1)]

4

slepton 質量行列の物理

超対称性理論

• μ- + (A,Z) → e- + (A,Z)• レプトン・フレーバー非保存過程：標準理論では禁止されている。

• ニュートリノ混合による高次効果は非常に小さい

• 標準理論を越える物理に敏感A. de Gouvea

5

理論的予想

Process CurrentLimit

SUSY-GUTlevel Future

µ N → e N 10-13 10-16 10-16,10-18

µ → e γ 10-11 10-14 10-13

τ → µ γ 10-6 10-9 10-8

PRISM/PRIME

MEG

Courtesy Hisano

PRISM/PRIME

MEG

SUSY+Seesaw, MSW Large Angle

SUSY-GUT

COMET COMET

!

"m2

ee !m2eµ !m2

e!

!m2µe m2

µµ !m2µ!

!m2! e !m2

! µ m2! !

#

$

Golden Trio

e

e

B~

mixing

large top Yukawa coupling

!0

"

!0

"

c-LFVg-2 EDM

Real Imaginary

τ-LFV

slepton mass matrix

Physics CapabilitiesJ-PARC PAC report

US P5 Report

COMET Overview

• Pulsed Proton Beam• π-b.g. suppression • J-PARC/MR

• Large μ yields

• J-PARC/MRonly 60 kW out of 450kW

• π-capture SC-solenoid• 1011 μ/s (PSI:108 μ/s)

• Curved-solenoid detector• Lower detector rate

• Upgradability to PRISM• add Phase-Rotator-Ring

Detector Section

Pion-Decay andMuon-Transport Section

Pion Capture SectionA section to capture pions with a large solid angle under a high solenoidal magnetic field by superconducting maget

A detector to search for muon-to-electron conver-sion processes.

A section to collect muons from decay of pions under a solenoi-dal magnetic field.

Stopping Target

Production Target

パルス陽子ビーム• バックグランド

• π-+(A,Z) → (A,Z-1)* → γ+(A,Z-1)，γ → e+ e- 　：一次陽子ビームに同期• μ- decay-in-flight, e- scattering, neutron streaming

• 信号• μ- +(A,Z) → e- +(A,Z) : 遅延 (~1μs)

Nbg = NP×Rext×Yπ/P×Aπ×Pγ×ANP : total # of protons (~1021)Rext : Extinction Ratio (10-9)Yπ/P : π yield per proton (0.015)Aπ : π acceptance (1.5×10-6)Pγ : Probability of γ from π (3.5×10-5)A : detector acceptance (0.18)

BR=10-16, Nbg < 0.12⇔ Extinction < 10-9

0.7 !s

パルス陽子 from J-PARC/MR

空バケツ法

Tomizawa Scheme• 8 GeV, 7 μA• Beam Pulsing

• Empty bucket Scheme• Bunched Slow Extraction

• Beam Emittance• V: Reduce RCS painting area• Reduce NP in a bunch:

small space charge effect• H: SX < 5π mm.mrad

• Proton Yield• High Repetition Rate

Extinction: < 10-9Power: 60 kW (4×1013 pps@8 GeV)

Pion Capture

• Tungsten Target• 16cm × 0.8cmφ

• water or radiation cooling• ΔE@Target: 3-4 kW• yields 0.002 stopping-μ-/proton (M. Yoshida)

Proton beam

100030

0

1400

3600

target

Z position along solenoid axis (cm)

Magne

tic fie

ld (Te

sla)

0

2

4

6

0 100 200 300

W shieldSC Coil

μ-yield vs. Bmax

p t (G

eV/c

)

pl (GeV/c)

pt (GeV/c)pt (GeV/c)

p (GeV/c)

π production rate

Curved Solenoid Spectrometer

Detector solenoid Traget solenoidCurved solenoidspectrometer

Collimator

105MeV/c60MeV/c

30MeV/c

Top view Side view0 20 40 60 80 100

Momentum (MeV/c)

Acce

ptanc

e0.1

0.2

0.3

0.4

0.5

0.6

0

Transmission efficiency

Eth (MeV)0 20 40 60 80 100

DIO

/Sto

ppin

g-µ

10-12

10-10

10-8

10-6

10-4

10-2

Detector Acceptance &Signal Sensitivity

AcceptanceGeometrical Acc. 0.73

Electron Transport 0.44pt > 52 MeV/c 0.67χ2 Cut (χ2 < 9) 0.86

Energy Selection 0.56Timing cut 0.38

Total 0.04

Proton Intensity 4 × 1013 HzRunning Time 2 × 107 sec

μ’s yields per proton 0.007μ-stopping efficiency 0.26

Total 1.5 × 1018 stopped μ’s

B(µ! + Al! e! + Al) =1

Nµ · fcap · Ae

•Nμ = 1.5 × 1018

•fcap = 0.6 for Aluminum•Ae = 0.04•B(μ- + Al → e- + Al) = 2.8 × 10-17

< 5 × 10-17 (90% C.L.)

Electron Momentum (MeV/c)100 101 102 103 104 105 106 107

Even

ts p

er 0.

192 M

eV/c

-310

-210

-110

1

10

210

310mu-e Conversion and Decay-in-Orbit

Decay-in-Orbit

mu-e Conversion Signal

(Still) Straw-man’s Layouts

J-PARCNP-Hall

DRAFT

Recent Activities• muon task force (chaired by S. Mihara)

• to address charges given by PAC• J-PARC/MR extinction study

• pulsed FX measurement: MR abort line• pulsed SX measurement: K1.8BR

• COMET location study

mu2e @Fermilab• mu2e(FNAL + xMECO)

• Revive of MECO• After the shutdown of Tevatron• Parasite on SNuMI-2

• 2012 ~• Renovate a Debuncher ring for

beam bunching• Single Event Sensitivity: 2×10-17

AP4 Line

AP5 LineA-D Line

まとめ• μ-e電子転換過程は標準理論を越えたc-LFV過程の一つであり、TeVスケールの物理を研究する為の重要な手段を提供する。

• 10-16まで探索すればイベントが見つかるかもしれない。• MEG(μ→eγ 探索@ PSI)とは相補的である。• COMET

• BR=10-16 で μN→eN を探索する実験• J-PARC/MRとハドロンホールを活用

• Fermilab/mu2eとCOMETの競争• muon-TF (chaired by S. Mihara)

• extinction study• location study

End of Slides