129 Xe 原子 EDM の探索実験について 吉見 彰洋 理研・応用原子核物理研 東工大.

Electric Dipole Moment d  0 T-violation CP-violation Non-zero EDM associated with spin Direct evidence of violation of time reversal symmetry s s Time reversal Time : t -t Spin : s -s EDM : d d CPT theorem Standard Model (SM) : Predicted EDM is about 10 5 smaller than the present experimental upper limit Beyond the SM : Detectable EDM Detection of non-zero EDM CP-violation beyond the standard model

EDM の検出 x z y B +E +t+t B=1 G, E=+10 kV/cm B=1 G, E= － 10 kV/cm Assuming d = ecm B +E B -E A difference of 1 cycle in 10 9 sec.  31years 259days 2hours n cycle n+1 cycle x z y EE tt B

Key issue for EDM experiment Thermal equilibriumSpin-polarized Production of spin polarization Detection of spin precession Long coherence time ….. Suppress the decoherence of the spin Suppression of ambient precession frequency shift In order to efficiently detect the spin precession…. Precise measurement of magnetic field  B = 1 pG  ≈ 1 nHz  d ≈ ecm spin precession Optical pumping Spin exchange Brute force :

Why the 129 Xe EDM ? (3) Self-sustained spin precession at low frequency (as shown below). Free Induction DecaySustained oscillation (2) Large polarization and long relaxation time achievable in the 129 Xe nucleus 129 Xe: Polarization P ≈ O(10-100) torr Relaxation: T 1 ≈ 20 min. Rapid decrease of the frequency width (1)Stable particle (as compared to   ≈ 15 min.)  high densities, atoms /cc  long observation times 3 He, 21 Ne, Ar, Kr, Xe, Rn J e = 0 I  0

EDM 測定上限値の推移 1.6  Hg d e (SM) ≈ Xe d ｎ (SM) ≈

Recent EDM experiment of diamagnetic atoms Vold et. al., Phys. Rev. Lett. 52 (1984) Rosenberry and Chupp, Phys. Rev. Lett. 86 (2001) Lamoreaux et. al., Phys. Rev. Lett. 59 (1987) Romalis et. al., Phys. Rev. Lett. 86 (2001) Operation of continuous spin maser One shot measurement … 2000 sec. Repetition of FID measurement …. 300 – 500 sec/1run

Production of spin-polarized 129 Xe nucleus W. Happer, Rev. Mod. Phys. 44 (1972) 169. Atomic polarization of Rb by optical pumping D1 line ： nm Two body collision with Rb atom Formation of van der Waals molecule with Rb Polarization transfer from Rb atom to Xe nuclei Selective excitation by circular polarized light through fermi-contact hyperfine interaction spin flip-flop Spin relaxation rate Spin exchange rate

Xe cell Cleaning  baking  Coating  Rb  Xe  confinement Coating agent : SurfaSil  suppression of the spin relaxation of Xe 100 torr Xe 10 2 torr Rb  mg Spin relaxation ： due to wall collision Non-coating ： T W ≈ 3 min. Coated cell ： T W ≈ 20 min. Glass cell  20 mm n  /cm 3

Rb Xe RbXe Transverse-polarization transfer : Rb atom Xe nuclei (re-polarization) Detection of 129 Xe nuclear precession Rb Xe  ’[Xe] = 7 × 10 3 /s,  sd = 0.2 /s 0.3 ms P Rb (ms) Time constant of spin transfer: s Precession frequency of < kHz Probe laser beam : single mode diode laser (794.7nm) After half-period precession Circular polarization (modulated by PEM)

129 Xe free precession signal (FID signal) Time (s) Signal (mV) Static magnetic field ： B 0 = 28.3 mG ( (Xe)=33.5 Hz) 90°RF pulse （ 33.5 Hz,  t = 3.0 ms, B 1 = 70 mG ) Transverse relaxation ： T 2 = 350 s ； （ collision with Rb atoms 、 field inhomogeneity ） T 2  350 s

Experimental apparatus Enriched 129 Xe : 230 torr Rb : ~ 1 mg P xe ~ 10 % 18 mm Xe gas cell Pyrex spherical grass cell SurfaSil coated Magnetic shield (3 layers ) Parmalloy Size : l = 100 cm, d = 36, 42, 48 cm Shielding factor : S = 10 3 Pumping LASER Tunable diode laser = nm ( Rb D1 line ),  = 3 nm Output: 18 W Probe LASER tunable diode laser with external cavity  = nm ( Rb D1 line ),  = nm Output: 15 mW Solenoid coil (for static field) B 0 = 28.3 mG ( I = 3.58 mA) PEM Mod. Freq. 50 kHz Si photo diode Freq. band width: 0 – 500 kHz NEP: 8  W/Hz Heater T cell = 60 ~ 70 ℃

Spin MASER Polarization vector : M Feedback field : B fb B0B0 Feedback torque Relaxation, pumping T2 relaxation Polarization’s growing (pumping effect) Feedback torque pump Feedback system Zeeman level Transverse magnetic field - synchronism with spin precession - Phase : perpendicular to the transverse polarization Amplitude : proportional to the transverse polarization Population inversion Feedback EM-field synchronism with emitted photon Polarization

Typical maser oscillation signal B 0 = 28.3 mG, ref = Hz, feedback gain : 18  G/0.1mV Feedback system ON Steady state oscillation Measured frequency : Signal (mV) Time (s) (  84 hours) Signal (V) Time (s)

Frequency (Hz) T 2 = 6.2 s T 2 = 240 s T 2 = 14.8 s  (deg) Frequency shift due to the feedback phase error Phase error of feedback field Frequency shift due to the feedback phase error  Ideal feedback field: T 2 =300 s,  = 0.1º  = 1  Hz  Feedback field spin

 (rad) t (sec)  = 0.96  Hz =  mHz VxVx VYVY    -3/2 Frequency precision (  Hz) to be improved (mA) Time (s)  I ~ 0.1  A for time scale of 1000 s (  B 0 ~ 0.8  G,  0 ( 129 Xe) ~ 1 mHz) ソレノイド電流（静磁場）の揺らぎ スピン歳差位相 Time (s) スピン歳差の観測から歳差位相を導く Measured frequency precision スピンメーザーの周波数特性

実験装置の改良 – magnetic shield - Construction of 4-layer shield l = 1600 mm, R =  400 mm Transverse: S ≈10 6 Longitudinal: S ≈10 4 Estimated shielding factor Measured residual field z (cm) Field (  G) longitudinal transverse Shielding factor : S ≈10 4

低ノイズ電流源の製作・テスト 基準電圧源の 標準ダイオード  低ノイズバッテリ  I ≈ 200nA  B ≈1.5  G  ≈ 1  Hz  I ≈ 5nA  B ≈30 nG  ≈ 25nHz PSE-1101 Ｔａｋａｓａｇｏ定電流源 上図の PSE-1101 のみを表示 5nA 200nA 静磁場生成ソレノイドマグネット への供給電流のノイズを減らす

Laser stabilization system Probe laser Linier polarizer Photo diode Photo elastic modulator Linier polarizer PEM driver Ref. in 100 kHz Sig. in Lock-in regulator Photo diode Shield Calibration cell Ref. cell Laser control Feedback modulation Fabry Perot interferometer SCULock-in Amp DC AC Solenoid Mini Solenoid 高精度磁力計の開発 Ref. cell on resonance Laser property Single mode diode laser (with extended cavity)

測定感度 最大回転角度 |B z | < 50 mG での傾き Time Constant 300ms Sensitivity 50mV レーザー強度 ・・・・・・・ 最大 ～ 15.6 mW 波長 ・・・・・・・・ 回転角度が最も大きくなる値に設定 ノイズ ・・・・・・・ SCU を用いてレーザー強度を正規化 シグナルの幅 回転角度 (mrad) 磁場 (G) Lock-in amp parameter V noise ～ 5.0×10 -4 V 回転角度に換算 φ noise ～ 2.9×10 -3 mrad 現在得られた最も大きいシグナル

今後の予定 新磁気シールド、静磁場電流源を用いて Xe スピンメーザー発振実験  I ≈ 5nA  B ≈30 nG  ≈ 25nHz  d ≈ ecm 電場印加系の製作・テスト 磁力計の感度向上 EDM 測定 Rb 原子のスピン緩和の抑制 sensitivity :  G/  Hz   B  G (  (Xe)  0.1 nHz )  Interaction with Rb atomic spins (10 9 /cc) P(Rb)  0.01 % ( re-polarization from Xe )   (Xe)  0.2 nHz (  T  0.01˚C)