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ミュオン g - 2/EDM の精密測定

ミュオン g - 2/EDM の精密測定. ２０１２年 ５ 月 １９ 日 三部 勉（ KEK ） J-PARC muon g-2/EDM collaboration. ミュオン異常磁気能率 g-2. 磁気 能率 ： 磁場に対する粒子（ スピン ）の応答 ミュオンの g 因子はディラック方程式では２であるが、 量子ループ によって２からずれる。. a μ = ( g-2)/2 =. + EW + Hadronic + BSM ?. m. m. ＋. ＝. ＋. ＋　 …. m. m. m. QED. 標準理論の予測から ３ σ のズレ.

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ミュオン g - 2/EDM の精密測定

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  1. ミュオンg-2/EDMの精密測定 ２０１２年５月１９日 三部勉（KEK） J-PARC muon g-2/EDM collaboration

  2. ミュオン異常磁気能率 g-2 • 磁気能率：磁場に対する粒子（スピン）の応答 • ミュオンのg因子はディラック方程式では２であるが、量子ループによって２からずれる。 aμ = (g-2)/2 = + EW + Hadronic + BSM ? m m ＋ ＝ ＋ ＋　… m m m QED 標準理論の予測から ３σのズレ 〜BNL E821(0.5ppm) 新たな実験で検証！ 野村大輔氏（東北大）の資料より HLMNT11 : J.Phys.G38:085003,2011

  3. Dark matter contribution? Davoudiasl, Lee, Marciano arXiv:1203.2947 • 宇宙観測実験 • 暗黒物質が必要 • 宇宙の構成物質のうち２２％を占める。 • その正体は依然として不明 • WIMPS (SUSY LSP) • Axion • … • ダークセクター • 新しいゲージ粒子 • 暗黒Zボソン (Zd) • Z-Zd混合によって測定にかかる可能性がある。 • 電子陽電子衝突 • パリティ非保存電子散乱 • K/B稀崩壊 • g-2

  4. g-2/EDMの測定 一様磁場中でミュオンが円運動する場合、 スピンはg-2分だけ、ミュオンより早く回転する。 この余剰な回転周期を測定してaμ (= (g-2)/2 ) を求める。 一般には電場が磁場に見える項やEDMによってもスピンは回転する。 J-PARC approach E = 0 BNL E821 approach γ=30(P=3 GeV/c) 電場ゼロの環境にすることで、 運動量に寄らず、g-2とEDMを測定できる

  5. J-PARC muon g-2/EDM 実験 物質生命科学実験施設(MLF) ミュオン基礎物理ビームライン（H-Line） 極冷 μ+ビーム: 強度　　106/sec 運動量　300 MeV/c (γ = 3) σ(pT)/p < 10-3 偏極度　>50% 概要＋極冷μ （三部） 陽子ビーム 極冷 μ+ビーム 、ミュオン蓄積磁石（３T） 蓄積磁石・検出器 入射・磁石 （飯沼） 蓄積磁石上側から極冷 μ+ビーム入射 パルスキッカーで磁石中心蓄積領域に静止し蓄積 崩壊μ+e+ννで生じる陽電子を陽電子飛跡検出器で33μs（5xミュオン寿命）の間測定 、陽電子飛跡検出器 測定器（上野）

  6. 入射、蓄積、陽電子検出 ミュオン蓄積磁石 ミュオンビーム入射位置 Anti-Helmholtz-type kicker (Pulse kick to stop spiral) Spiral injection Magnet coil (3T) ν kicker detector e+ Positron tracker ν mm

  7. 予想される陽電子の時間分布 磁場中で、ミュオンのスピンは時間と共に歳差運動。  高エネルギーの陽電子数も同じ周波数で変化する。 p>200 MeV/c １年間(107sec)測定 w e+ decay time (sec)

  8. Expected time spectrum of me+nn decay • EDMがあると歳差運動の軸が磁場方向から傾く • 崩壊陽電子が磁場方向に対して上下の非対称に生じる p>200 MeV/c １年間(107sec)測定 w Up-down asymmetry ∝EDM dm=2E-20 e・cm e+ decay time (sec)

  9. Collaboration (Contributors to CDR) • 92 members ( …still evolving) • 25 Institutions: KEK, RIKEN, U-Tokyo, TRIUMF, BNL, PMCU, CYCRC-Tohoku, Osaka, Rikkyo, TITech, SUNYSB, RAL, UCR, UNM, Victoria • 7 countries: Czech, USA, Russia, Japan, UK, Canada, France The stage-1 approved in IMSS PAC, and stage-1 recommended in IPNS PAC.

  10. Ultra-slow muons for g-2/EDM • Pointing power • No focusing field pT/p < 10-5 @p=300 MeV/c • Momentum pT< 3 keV/c p = (3/2)1/2pT < 3.7 keV/c • Kinetic energy E < 0.065 eV • Temperature T < 750 K (2000 K (hot-W)@RIKEN-RAL ) • This condition could be relaxed if very-weak focusing is applied (hot-W would be ok too). • Intensity • Statistical uncertainty on aμ = 0.1 ppm (goal)  1013muons/year  106 ultra-slow muon /sec (25/sec @RIKEN-RAL) • Polarization • Figure-of-Merit = NP2 • 50 100% (50% @RIKEN-RAL)

  11. Ultra-slow muons for g-2/EDM Requirements: 40000 times more muons, and Coolermuon than RIKEN-RAL (not mandatory)

  12. Ultra-slow muons for g-2/EDM Requirements: 40000 times more muons, and Coolermuon than RIKEN-RAL (not mandatory) 170 times higher surface muon per spill at J-PARC H-line 2.4 x 104/spill  400 x 104/spill (25 spill/sec) Room temperature target (hot tangsten silica aerogel?) 2000K (15keV/c)  300K (2.3keV/c) 100 times intense Ly-αlaser 1mJ 100mJ 4x104 ultra-cold muon/spill with p=2.3keV/c

  13. Room-temperature muonium emitter • Silica powders (SiO2) • Structure : network of SiO2 grain Large surface area. • Known to be a good Mu emitter at room temp. • Not self-standing  difficulty in laser ionization. • Silica aerogel • Similar structure of SiO2 grain-network. • Self-standing! • Control of density and thickness • Only few (and old) data available • Vacuum yield and space-time distributions with their density dependence were measured at TRIUMF.

  14. Space-time distribution of Mu Reconstructed Mu decay vertex position • Silica plate data is used to estimate the background distribution. • Enhancement in aerogel data is due to Mu emission in vacuum. • Mu signals are observed in all aerogel densities. ● Aerogel 27mg/cc ● Silica plate Preliminary Distance from target surface Target surface

  15. Back of envelope estimate of efficiencies from surface to ultra-cold muons S1249 (2011, TRIUMF) Woodle, et al. (88, PSI) Mills, et al. (86, KEK-MSL) Beer, et al. (89, TRIUMF) Straggling Preliminary Required yield : 1.E+6/s a factor of 8 behind ?

  16. Prospects on Mu target developments • Aerogels • Squeeze as much information as possible from S1249 data • Density dependence, space-time distributions etc… • More surface area • Porous structure? • New PSI work on meso-porous Silica (arXiv:1112.4887) • Micro-drilled W-foil • 10μm-pitch drilled foil was tried at RIKEN-RAL • Started R&D for 1μm pitch for further gain • Surface conditions • W coated with alkali-metal (Na, Cs) • By Prof. Y. Miyake, Prof. Y.Nagashimaet al. wikipedia RIKEN-RAL

  17. Laser development and ionization test • Laser development at RIKEN • Omega-1 • Fiber Laser System • Solid State Amplifier • Non-linear frequency converter • Omega-2 • SLM Seeder • 1st and 2nd Non-linear amplification • 2-photon resonant 4-wave mixing in Kr cell • Ionization test at RIKEN-RAL • Improved laser system • stable, more freedom of adjustments • New beam line controls • Heater system refurbished • Data being collected (March, May-June) To be tested and installed to U-line in 2012

  18. まとめ • A new muon g-2/EDM experiment at J-PARC: • Off magic momentum + compact g-2 ring • Complementary to FNAL g-2 • Start in 2016 • Ultra-slow muons • The key technology to realize required beam • TRIUMF S1249 studies Mu emitting materials at room temp. • Mu from hot W at J-PARC in progress • Ionization test with improved laser system is in progress at RIKEN-RAL. • Intense Ly-α laser being developed in close collaboration with U-line developers.

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