129 Xe magnetometry for KEK-RCNP neutron EDM measurements M. Mihara, K. Matsuta (Osaka Univ.) Y. Masuda, S.C. Jeong, Y.X. Watanabe, S. Kawasaki (KEK) K. Hatanaka, R. Matsumiya (RCNP, Osaka Univ.) K. Asahi (TIT) C. Bidnosti (Winipeg Univ.) Y. Shin (TRIUMF) Workshop on nEDM Experimental Tecniques, Oct , 2012, ORNL

nEDM measurements with 129 Xe comagnetometer n 129 Xe EDM cell B E+E+ E–E– ν n = (2μ n B ± 2d n E)/h ν Xe = (2μ Xe B ± 2d Xe E)/h (ν n /ν Xe ) E + (ν n /ν Xe ) E – ≒ hν Xe γnγn γ Xe d meas E d n – d Xe γ Xe γnγn ~10 –28 e ･ cm ~10 –11 B = 1μT E = 10 kV/cm = ~29 Hz = ~12 Hz ~0.5 nHz +(0.7±3.3)x10 –27 e ･ cm Rosemberry & Chupp PRL86(2001)22

GPE for 129 Xe Buffer gas effect suppresses GPE 129 Xe mean free path λ (= 1/nσ) = 0.7~5 x /cc (7 mTorr)

GPE for 129 Xe Suppression factor S = (T d /T L ) –2 = 6 x 10 –4 d f ∝ (∂B 0z /∂z)R 2 /c 2 · S d fXe = ~0.9 x 10 –28 ecm B 0 = 2 µT ∂B 0z /∂z = 2 nT/m R = 0.25 m v xy = 240 λ = 0.7 mm diffusion time T d = (2R) 2 /(v xy λ) ~1.5 s Larmor precession time T L = 2π/ω 0 ~40 ms cf. d fHg = ~5 x 10 –26 ecm PLA376(2012)1347

129 Xe polarization system of Asahi (TIT) group. We will apply a part of this apparatus to co-magnetometry in nEDM. Xe FID signal Detection system will be replaced by SQUID or SERF or NMOR T 1 = 1000 s, T 2 = 350 s 50%

Polarize 129 Xe in EDM cell Rb-Xe [ 129 Xe] = ~2.5 x cm –3 T 1, T 2 > ~100 s N 2 free Measure 129 Xe precession SQUID probe laser

Polarize 129 Xe nuclear spin Optical pumping van der Waals molecule

Effect of N 2 buffer gas Rosenberry et al., PRA75(2007) N2N2 N2N2 Buffer gas N 2 : reduce absorption of de-exciting unpolarized photons Ruth et al., Appl. Phys. B 68 (1999) 93 Xe + N 2 + Rb N2N2 Plarization of Rb atoms Polarization of 129 Xe nuclei

Plan of 129 Xe magnetometer No buffer gas (N 2 ) in EDM cell pump laser probe laser V±V± UCN guide EDM cell (Xe: 7 mTorr) detector B 129 Xe & Rb External cell: EDM cell Xe: 7 mTorr (2.5 x cm -3 ) Total amount of Xe gas: 〜 20 liter (EDM cell + UCN guide) External cell: 7 Torr / 20 cm 3 T 2 > ~100 s polarize 129 Xe

Freeze-pump-thaw separation LN 2 probe laser pump laser Xe N2N2 pump ・ Xe + N 2 mixture in polarizing cell ・ Solidify Xe ・ Evacuate N 2 gas ・ Transport polarized 129 Xe into EDM cell Xe, N 2 Rb N 2 free Appl. Phys. B 68 (1999) 93

Rb-K mixture → 21 Ne polarization x 10

pump laser probe laser

129 Xe nuclear spin relaxation in EDM cell 1/T 2 = 1/T 1 + 1/T 2,field ∝ R 4 /D x | ∇ B| 2 ~10 pT/cm ∝ p –1 1/T 1 = 1/T 1,Xe-Rb + 1/T 1,Xe-Xe + 1/T 1,wall 1/T 1,Xe-Rb = (γ M ζ/[Xe] + ) [Rb] s –1 vdW ~10 –11 collision ~10 –16 = ~1/(10 s) (T = 300 K) [Cates et al., PRA45(1992)4631] 1/T 1,Xe-Xe = 1/(4.1 h) [Chann et al., PRL88(2002)113201] 1/T 1,wall = 1/(3 h) ~ 1/(several h) [Xe] = 2.5 x cm –3 (7 mTorr) [Rb] = 1 x cm –3 (T = 300 K) [Gemmel et al., EPJ D57(2010)303]

Measurement of P Xe, T 1

AFP-NMR B0B0 B1B1 Pickup coil RFcoil B 0 coil cell

Proton NMR (H 2 O) Lock-in amp. out B0B0 5 s ν L (proton) = 48 G

Rb & Xe transfer system Ti-sapphire & Ar laser Semiconductor laser

summary GPE for 129 Xe comagnetometer was discussed. Buffer gas effect suppresses GPE to d fxe ~10 –28 ecm. How to realize the 129 Xe comagnetomter is under consideration. But, N 2 free 129 Xe polarization may be possible. R & D has been just started. Precision measurements of NMR frequency ratio ω n /ω Xe are planed to determine g factor of 129 Xe and field gradient.

Spin exchange rate in exernal cell [Xe] = 2.5 x cm –3 (7 Torr), [N 2 ] = 3.5 x cm –3 (100 Torr) [Rb] = 3 x cm –3 (T = 400 K) P Xe (t) = P Rb (1 + Γ/γ se ) –1 x exp{–(Γ + γ se )t} P Rb (t) = (1 + Γ sd /γ + ) –1 x exp{–(Γ sd + γ + )t} Γ sd ; spin destruction rate of Rb atom γ + ; production rate of m J = +1/2 Γ; wall relaxation & Xe-Xe vdW γ se ; Rb-Xe spin exchange rate ( ) ( ) Γ sd = γ Xe-Rb [Xe] + γ Rb-Rb [Rb] + γ N2-Rb [N 2 ] = 1.2 x 10 3 s – γ se = γ Xe-Rb [Rb] = 0.13 s –1 [Wagshul & Chupp, RRA49(1994)3854] [Cates et al., PRA45(1992)4631]

Polarize 129 Xe nuclear spin Optical pumping m J = –1/2 m J = +1/2 σ+σ+ 5S 1/2 5P 1/ nm Energy levels of Rb atom λ = nm Rb 129 Xe σ+σ+ P Xe ≈ P Rb (1 + Γ/γ se ) –1 P Rb ≈ (1 + Γ sd /γ + ) –1 Γ sd ; spin destruction rate of Rb atom γ + ; production rate of m J = +1/2 Γ; 129 Xe relaxation rate except γ se γ se ; Rb-Xe spin exchange rate ( ) ( )

129 Xe magnetometer Polarize 129 Xe before storing UCN 129 Xe B B Measure ν Xe during Ramsey resonance （ 90° pulse ） T 2 > t c T 1 >> t c

現状および今後の計画 KEK→ 阪大に移設済 レーザー装置 テストセル製作用真空装置 テストセルを製作 バッファーガス無しで可能か？ 偏極度, 緩和時間 (T 1, T 2 ) 測定 ↔ 最適化

Our approach to nEDM B B 129 Xe magnetization rμrμ = μ 0 /4π (3 r ( μ ∙ r ) - μ r 2 )/r 5 = 0.98× T at r = 0.1 m μ 2.5×10 16 /liter 129 Xe μ = × J/T S = 0.01 m 2 Φ = Φ 0 cos(ω 0 t) Φ 0 = h/2e = × Tm 2 We need to develop SQUID 1fT, 5μΦ 0 /√Hz vibration? SERF Cs magnetometer vibration small effect BoBo Observation of 129 Xe spin precession in the EDM cell EDM cell We have experience of Xe polarization by means of spin exchange optical pumping. SQUID or SERF or NMOR If 50% polarization, p =7x Torr, V =3 litters, B = 150 fT

PRA75(2007)023401

原案 ①: 直接法 Xe: 7 mTorr (2.5 x cm -3 ) Diffusion time: t d = (2R) 2 /(v xy λ) R = 0.25 m v xy = 158 m/s λ = 0.5 mm = ~ 3 s No buffer gas → P Xe ? pump laser probe laser

Appl. Phys. B 68 (1999) 93