Xe nuclear spin maser and search for atomic EDM

Transcription

1 Xe nuclear spin maser and search for atomic EDM T. Inoue, A. Yoshimi *, M. Uchida, T. Furukawa, N. Hatakeyama, M. Tsuchiya, H. Hayashi, and K. Asahi Department of Physics, Tokyo Institute of Technology * Nishina Accelerator Research Center, RIKEN Workshop on Symmetry and Symmetry Japan 30. Jul. 2009

2 Outline What s EDM - EDM and T-violation - Status of EDM experiment - Classification of EDM Xe Nuclear Spin Maser - Principles of EDM measurement - Experimental setup - Optical pumping and optical detection - Active spin maser Experimental Result - Present status of active spin maser On going R&D Summary and Future

3 Electric Dipole Moment (EDM) Non-zero EDM associated with spin is direct evidence of time reversal symmetry violation d s d -s Classical representation e d = rρ particle ( r) d r Time reversal : T Time Spin EDM : : : t -t s -s d d Vector (parallel to spin) d = dsˆ d 0:T-violation CP-violation (by CPT theorem) EDM : sensitive to the CP-violation beyond SM Standard Model (SM) : Predicted neutron EDM is about 10 5 smaller than the present experimental upper limits. Beyond SM : Detectable EDM Search for EDM Test of the SM and beyond SM (no SM background)

4 Historical limits of EDMs d n < ecm C.A. Baker et al., PRL. 97 (2006) Neutron EDM predicted values d( Xe) < ecm Rosenberry and Chupp, PRL 86 (2001) 22 d( 199 Hg) < ecm W.C. Griffith et al., PRL 102 (2009) Standard Model (d n = ~ ecm) Pendlebury and Hinds, NIM A 440 (00) 471

5 EDM of what? M. Pospelov and A. Ritz, Annals of Phys. 318, (2005) Neutron Direct measurement of nucleon EDM Unstable particle : τ 1/2 = s Density extremely low : ρ UCN/cm -3 Tl, Fr, Cs Xe, 199 Hg, Rn, Ra Diamagnetic Atom ( Xe, 199 Hg, Rn, Ra ) Stable particle Nuclear Schiff moment d n, θ QCD, d q, d q color Paramagnetic Atom Directly related to the electron EDM, d e

6 Principles of EDM measurement Energy shift according to E direction Hamiltonian:H = μ B d E E parallel to B H = μb de E anti-parallel to B H = μb + de 1 m = 2 B 0 E = 0 B 0 E // B B 0 E // B Small shift of spin precession frequency B = 0 E = 0 h ν 0 hν + hν + 2 μb + 2dE = h ν ( E // B) 2μB 2dE = h ν ( E // B) EDM measurement measurement of difference between frequency shifts Δν = ν + ν = 4dE h 1 m = 2 ν + B E s ν B E s

7 Key issue for a high-sensitivity EDM detection Long measurement time of spin precession <= Nuclear Spin Maser 1. Accumulation of free spin precession Transverse spin δν ind 1 1 1/ 2 δν final = = = Tm n n T 2. Continuous spin precession (maser oscillation) Transverse spin T T T δν final T m δφ = T T m 3/ 2 m Xe atom : Maser scheme applicable!!

8 Experimental apparatus Magnetic shield (4 layers ) Atomic polarization of Si photo diode Parmalloy Rb atoms (Fe-Ni alloy) by using optical pumping technique Freq. band width : 0 ~ 500 khz NEP : 8 m /2 W/Hz s = m s = + 1/2 5P 1/2 5S 1/2 σ + : nm Signal [mv] m s = -1/2 m s = + 1/2 Rb atomic energy level Selective excitation by circularly polarized light Probe light :794.7nm Xe gas cell Circular pol (modulated by PEM) 18 mm Xe nuclear spin polarization 5P 1/2 5S 1/2 Xe Transmission : 230 torr Max N 2 : 100 torr Rb : ~ 1 mg Pyrex glass cell SurfaSil coated B 0 Solenoid coil Nuclear (for static polarization field) by B spin 0 = 30.6 exchange mg (I = interaction ma) with Rb atom N 2 Rb PEM Xe Circularly Rb polarizing Xe plate I Rb T 2 80 s SHeater Xe N 2 Xe Optical detection of nuclear spin precession Xe Rb B 0 Xe Xe Typical Xe free precession signal Transverse polarization transfer : Xe nuclei Rb atoms (re-polarization) After half period of Xe spin precession Xe Probe laser Rb DFB Laser wave length : nm (Rb D1 Line) Xe Δλ = nm output : 15 mw T 70 o C Rb Pumping laser wavelength : nm (Rb D1 Line) Rb Δλ = 3 nm output : 11 W B 0 Xe Xe Transmission Min

9 Magnetic shield (4 layers) φ : 400 mm, L = 1600 mm for the outermost layer Solenoid coil φ : 254 mm, L = 940 mm Feedback coil Pumping laser PEM Xe gas cell Heater - tube Probe laser

10 Nuclear Spin Maser Conventional Nuclear Spin Maser Strong coupling between nuclear spins and feedback coil Richards et al., (1988) : 3 He spin maser Chupp et al., (1994) : Xe spin maser Static magnetic field : B 0 ~ G Feed back field Feedback coil L Torque from B Static magnetic field : B 0 mg Probe light Active Nuclear Spin Maser Effect Artificial from feedback by using the optical detected signal Yoshimi et al., (2002) B 0 relaxation + pumping ν 0 P(t) Feedback system Feedback circuit Induced current I npq Pumping light γ B Operation Condition 1 1 = γ ημ0hi[ n] P0 Q > τ 2 T RD Radiation dumping time 2 1 ν > khz (B 0 > 1 G) 2 Capacitor C 0 = 1 LC transverse relaxation time Feedback coil P (t) Pumping light Photo diode Lock-in detection Spin precession signal B (t) Maser operation in low static field (~ mg) Small field fluctuation small frequency fluctuation

11 Maser Oscillation Signal Feedback system on B 0 = 30.6 mg ν 0 = 36.0 Hz Signal [mv] Star-up enhancement Steady oscillation Signal [mv] Signal [mv]

12 Frequency analysis Lock-in Amp outputs Signal [mv] V X V Y 10-4 Measured frequency precision Phase [rad] 1 VY ( t) φ( t) = tan = 2π ( ν ref ν 0) t + ( φref φ0) V ( t) X Precession phase Frequency precision [Hz] Δν T 1 m Δν T 3/ 2 m EDM (E = 10 kv/cm) [ecm] ν ref ν0 = ± Hz Frequency precision :9.3 nhz (T m = s) EDM precision : ecm (E = 10kV/cm) for one week measurement : δν ~0.1 nhz δd ~ ecm Measurement time [s]

13 Frequency stability for a long term measurement why δν τ -1/2 in t > 1000 s? why δν get worse in t > s? Frequency fluctuation in 1000s-avaraging Drift of maser frequency Frequency [mhz] 100 μhz Frequency [mhz] 2 mhz (Now investigating) 1.5 mhz 1.) drift of solenoid current in 1000 s time scale 10 na ; 40 ng 50 μhz 2.) drift of environmental magnetic field in 1000 s time scale 100 μg 100 ng 125 μhz (shielding factor : ~ 10 3 ) Current [ma] Drift of solenoid current 350 na ; 1.4 µg ~ 1.6 mhz

14 We are now introducing a digitalized feedback system to the active spin maser scheme constructing highly sensitive magnetometer producing and testing a double cell (pumping part and operation part) and testing the Xe polarization stabilizing a temperature of current source constructing a cell temperature control system

15 We are now introducing a digitalized feedback system to the active spin maser scheme constructing highly sensitive magnetometer producing and testing a double cell (pumping part and operation part) and testing the Xe polarization stabilizing a temperature of current source constructing a cell temperature control system

16 Ongoing R&D1 : Digitalized feedback system CPU : HD64F7144F50 ADC : ADS7808U DAC : DAC7641U CPU ADC DAC Input Output B 0 = 4.2 mg ν 0 = 5.0 Hz Signal [V]

17 Ongoing R&D2 : Rb RIKEN Nonlinear Magneto-Optical Rotation (NMOR) of Rb atom Highly sensitive magnetometer δb ~ 10 G/ Hz δd ~ 10 ecm ( E = 10 kv/cm) D. Budker et al.,pra 62 (2000) First : Faraday Rotation Spectrum 4.0 Linear polarized light k Faraday rotation Spectrum of Rb 85 Rb D1, F=3 B Rb atom Faraday rotation Rb cell Rotation angle (mrad) Magnetic field (G)

18 Summary and Future prospects By using the active spin maser, the frequency precision of 9.3 nhz has been obtained for a measurement time of 30,000 s. It corresponds to the EDM precision of ecm, when E = 10 kv/cm. The digitalized feedback system has been introduced to the active spin maser scheme, and it has been successfully operated. The Rb magnetometer based on NMOR is being constructed. The Faraday rotation was measured in the range of a few G. Further improvements and developments are now being proceeded : Double cell (pumping and operation part) for maser operation, Temperature control of solenoid current source, Electric field application d( Xe) = ~ ecm. ( 0.1 nhz).