129 Xe magnetometry for KEK-RCNP neutron EDM measurements

1. Workshop on nEDMExperimental Tecniques, Oct. 11-13, 2012, ORNL 129Xe magnetometryfor 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)

3. nEDM measurements with 129Xe comagnetometer EDM cell ~0.5 nHz νn = (2μnB ± 2dnE)/h n = ~29 Hz νXe= (2μXeB ± 2dXeE)/h E– E+ B = ~12 Hz 129Xe B = 1μT E= 10 kV/cm γn dn–dXe γXe ~10–28e･cm γXe (νn/νXe)E+ 1 ≒ 1 + 4 dmeasE γn hνXe (νn/νXe)E– +(0.7±3.3)x10–27e･cm Rosemberry & Chupp PRL86(2001)22 ~10–11

4. GPE for 129Xe 129Xe mean free path λ (= 1/nσ) = 0.7~5 mm @2.5 x 1014 /cc (7 mTorr) Buffer gas effect suppresses GPE

5. GPE for 129Xe PLA376(2012)1347 df∝ (∂B0z/∂z)R2/c2 · S Suppression factor S = (Td/TL)–2= 6 x 10–4 diffusion time Td = (2R)2/(vxyλ) ~1.5 s Larmor precession time TL = 2π/ω0 ~40 ms B0 = 2 µT ∂B0z/∂z = 2 nT/m R = 0.25 m vxy = 240 m/s@300K λ = 0.7 mm dfXe = ~0.9 x 10–28ecm cf. dfHg = ~5 x 10–26ecm

7. 129Xe polarization system of Asahi (TIT) group. We will apply a part of this apparatus to co-magnetometry in nEDM. Detection system will be replaced by SQUID or SERF or NMOR 50% T1 = 1000 s, T2 = 350 s Xe FID signal

8. Polarize 129Xe in EDM cell Rb-Xe [129Xe] = ~2.5 x 1014 cm–3 T1, T2 > ~100 s N2 free • Measure 129Xe precession SQUID probe laser

9. Polarize 129Xe nuclear spin van der Waals molecule Optical pumping

10. Effect of N2 buffer gas Polarization of 129Xe nuclei Plarization of Rb atoms N2 Xe + N2 + Rb N2 Ruth et al., Appl. Phys. B 68 (1999) 93 Buffer gas N2: reduce absorption of de-exciting unpolarized photons N2 Rosenberry et al., PRA75(2007)023401

11. Plan of 129Xe magnetometer T2 > ~100 s EDM cell (Xe: 7 mTorr) B V± probe laser External cell: polarize 129Xe detector Total amount of Xe gas: 〜20 liter(EDM cell + UCN guide) 129Xe & Rb EDM cell Xe: 7 mTorr (2.5 x 1014 cm-3) pump laser External cell: 7 Torr / 20 cm3 UCN guide No buffer gas (N2) in EDM cell

12. Freeze-pump-thaw separation N2free Xe, N2 Rb probe laser Appl. Phys. B 68 (1999) 93 pump laser ・Xe + N2mixture in polarizing cell ・ Solidify Xe ・Evacuate N2gas ・ Transport polarized 129Xe into EDM cell N2 Xe pump LN2

13. Appl. Phys. B 68 (1999) 93

14. Rb-K mixture → 21Ne polarization x 10

15. pump laser probe laser

17. 129Xe nuclear spinrelaxation in EDM cell [Xe] = 2.5 x 1014 cm–3 (7 mTorr) [Rb] = 1 x 1010 cm–3 (T = 300 K) 1/T1 = 1/T1,Xe-Rb + 1/T1,Xe-Xe + 1/T1,wall 1/T1,Xe-Rb= (γMζ/[Xe] + <σsev>) [Rb] s–1 vdW ~10–11 collision ~10–16 = ~1/(10 s) (T = 300 K) [Cates et al., PRA45(1992)4631] 1/T1,Xe-Xe = 1/(4.1 h) [Chann et al., PRL88(2002)113201] 1/T1,wall = 1/(3 h) 1/T2 = 1/T1 + 1/T2,field ∝ R4/D x |∇B|2 ~10 pT/cm ~ 1/(several h) ∝ p–1 [Gemmel et al., EPJ D57(2010)303]

18. Measurement of PXe, T1

19. AFP-NMR cell RFcoil B0 B1 Pickup coil B0coil

20. Proton NMR (H2O) νL(proton) = 48 kHz@11.2 G Lock-in amp. out 5 s B0

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

24. summary • GPE for 129Xe comagnetometer was discussed. • Buffer gas effect suppresses GPE to dfxe ~10–28ecm. • How to realize the 129Xe comagnetomter is under consideration. But, N2 free 129Xe polarization may be possible. • R & D has been just started. • Precision measurements of NMR frequency ratio ωn/ωXe are planed to determine g factor of 129Xe and field gradient.

27. Spin exchange rate in exernal cell [Xe] = 2.5 x 1017 cm–3 (7 Torr), [N2] = 3.5 x 1018 cm–3 (100 Torr) [Rb] = 3 x 1013 cm–3 (T = 400 K) PRb(t) = (1 + Γsd/γ+)–1 x exp{–(Γsd + γ+)t} ( ) Γsd; spin destruction rate of Rb atom γ+; production rate of mJ = +1/2 PXe(t) = PRb(1 + Γ/γse)–1 x exp{–(Γ + γse)t} ( ) Γ; wall relaxation & Xe-XevdW γse; Rb-Xe spin exchange rate Γsd= γXe-Rb[Xe] + γRb-Rb[Rb] + γN2-Rb[N2] = 1.2 x 103 s–1 33 24 1100 [Wagshul & Chupp, RRA49(1994)3854] [Cates et al., PRA45(1992)4631] γse = γXe-Rb[Rb] = 0.13 s–1

29. Polarize 129Xe nuclear spin Optical pumping 5P1/2 129Xe Rb σ+ 794.7 nm σ+ 5S1/2 λ = 794.7 nm mJ = –1/2 mJ = +1/2 Energy levels of Rb atom ( ) Γsd; spin destruction rate of Rb atom γ+; production rate of mJ = +1/2 PRb ≈ (1 + Γsd/γ+)–1 ( ) Γ; 129Xe relaxation rate except γse γse; Rb-Xe spin exchange rate PXe ≈ PRb(1 + Γ/γse)–1

30. 129Xemagnetometer 129Xe 129Xe （90° pulse） B B Measure νXe during Ramsey resonance Polarize 129Xe before storing UCN T2 > tc T1 >> tc

32. 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 (T1, T2) 測定　↔　最適化

33. If 50% polarization, p =7x 10-3Torr, V =3 litters, B = 150 fT Our approach to nEDM Observation of 129Xe spin precession in the EDM cell Bo We have experience of Xe polarization by means of spin exchange optical pumping. 2.5×1016/liter 129Xe μ = -3.9239×10-27 J/T μ B 129Xe magnetization = μ0/4π (3r(μ∙r) - μr2)/r5 = 0.98×10-14 T at r = 0.1 m EDM cell We need to develop SQUID 1fT, 5μΦ0/√Hz vibration? SERF Cs magnetometer vibration small effect S = 0.01 m2 Φ= 0.047 Φ0 cos(ω0t) Φ0 = h/2e = 2.067833667×10-15 Tm2 SQUID or SERF or NMOR

35. PRA75(2007)023401

36. 原案①: 直接法 pump laser Xe: 7 mTorr (2.5 x 1014 cm-3) probe laser Diffusion time: td = (2R)2/(vxyλ) = ~3 s R = 0.25 m vxy = 158 m/s λ = 0.5 mm No buffer gas →PXe ?

37. Appl. Phys. B 68 (1999) 93

38. Appl. Phys. B 68 (1999) 93