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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)
Workshop on nEDM Experimental Tecniques, Oct. 11-13, 2012, ORNL
nEDM measurements with 129Xe comagnetometer
n
129Xe
EDM cell
B E+ E–
νn = (2μnB ± 2dnE)/h
νXe= (2μXeB ± 2dXeE)/h
(νn/νXe)E+
(νn/νXe)E–
≒ 1 + 41hνXe γn
γXedmeasE
dn– dXeγXe
γn
~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 ･ cmRosemberry & Chupp
PRL86(2001)22
GPE for 129Xe
Buffer gas effect suppresses GPE
129Xe mean free path λ (= 1/nσ) = 0.7~5 mm
@2.5 x 1014 /cc (7 mTorr)
GPE for 129Xe
Suppression factor S = (Td/TL)–2 = 6 x 10–4
df ∝ (∂B0z/∂z)R2/c2 · S
dfXe = ~0.9 x 10–28 ecmB0 = 2 µT∂B0z/∂z = 2 nT/mR = 0.25 mvxy = 240 m/s@300Kλ = 0.7 mm
diffusion time Td = (2R)2/(vxyλ) ~1.5 s
Larmor precession time TL = 2π/ω0 ~40 ms
cf. dfHg = ~5 x 10–26 ecm
PLA376(2012)1347
129Xe 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
T1 = 1000 s, T2 = 350 s
50%
• 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
Polarize 129Xe nuclear spin
Optical pumping
van der Waals molecule
Effect of N2 buffer gas
Rosenberry et al., PRA75(2007)023401
N2
N2
Buffer gas N2: reduce absorption of de-exciting unpolarized photons
Ruth et al., Appl. Phys. B 68 (1999) 93
Xe + N2 + Rb
N2
Plarization of Rb atoms Polarization of 129Xe nuclei
Plan of 129Xe magnetometer
No buffer gas (N2) in EDM cell
pump laser
probe laser
V±
UCN guide
EDM cell (Xe: 7 mTorr)
detector
B
129Xe & Rb
External cell:
EDM cell Xe: 7 mTorr (2.5 x 1014 cm-3)
Total amount of Xe gas: 〜 20 liter (EDM cell + UCN guide)
External cell: 7 Torr / 20 cm3
T2 > ~100 s
polarize 129Xe
Freeze-pump-thaw separation
LN2
probelaser
pump laser
Xe N2pump
・ Xe + N2 mixture in polarizing cell
・ Solidify Xe・ Evacuate N2 gas
・ Transport polarized 129Xe into
EDM cell
Xe, N2
Rb
N2 free
Appl. Phys. B 68 (1999) 93
Appl. Phys. B 68 (1999) 93
Rb-K mixture → 21Ne polarization x 10
pump laser
probe laser
129Xe nuclear spin relaxation in EDM cell
1/T2 = 1/T1 + 1/T2,field ∝ R4/D x |∇B|2
~10 pT/cm∝ p–1
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/(several h)
[Xe] = 2.5 x 1014 cm–3 (7 mTorr)[Rb] = 1 x 1010 cm–3 (T = 300 K)
[Gemmel et al., EPJ D57(2010)303]
Measurement of PXe, T1
AFP-NMR
B0
B1Pickup coil
RFcoil
B0 coil
cell
Rb & Xe transfer system
Ti-sapphire & Ar laser
Semiconductor laser
summary
• GPE for 129Xe comagnetometer was discussed.• Buffer gas effect suppresses GPE to dfxe ~10–28 ecm.
• 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.
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)
PXe(t) = PRb (1 + Γ/γse)–1 x exp{–(Γ + γse)t}
PRb(t) = (1 + Γsd/γ+)–1 x exp{–(Γsd + γ+)t}
Γsd; spin destruction rate of Rb atomγ+; production rate of mJ = +1/2
Γ; wall relaxation & Xe-Xe vdWγse; Rb-Xe spin exchange rate( )
( )
Γsd = γXe-Rb[Xe] + γRb-Rb[Rb] + γN2-Rb[N2] = 1.2 x 103 s–1
1100 24 33
γse = γXe-Rb[Rb] = 0.13 s–1[Wagshul & Chupp, RRA49(1994)3854][Cates et al., PRA45(1992)4631]
Polarize 129Xe nuclear spinOptical pumping
mJ = –1/2 mJ = +1/2
σ+
5S1/2
5P1/2
79
4.7
nm
Energy levels of Rb atom
λ = 794.7 nm
Rb129Xe
σ+
PXe ≈ PRb (1 + Γ/γse)–1
PRb ≈ (1 + Γsd/γ+)–1 Γsd; spin destruction rate of Rb atomγ+; production rate of mJ = +1/2
Γ; 129Xe relaxation rate except γse
γse; Rb-Xe spin exchange rate( )
( )
129Xe magnetometer
Polarize 129Xe before storing UCN
129Xe 129Xe
B B
Measure νXe during Ramsey resonance
（ 90° pulse ）
T2 > tc
T1 >> tc
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
Our approach to nEDM
B 129Xe magnetization= μ0/4π (3r(μ∙r) - μr2)/r5
= 0.98×10-14 T at r = 0.1 m
μ
2.5×1016/liter 129Xeμ = -3.9239×10-27 J/T
S = 0.01 m2
Φ = 0.047 Φ0 cos(ω0t) Φ0 = h/2e = 2.067833667×10-15 Tm2
We need to developSQUID 1fT, 5μΦ0/√Hzvibration?SERF Cs magnetometervibration small effect
Bo
Observation of 129Xe 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 10-3 Torr, V =3 litters, B = 150 fT
PRA75(2007)023401
原案① : 直接法
Xe: 7 mTorr (2.5 x 1014 cm-3)
Diffusion time: td = (2R)2/(vxyλ)
R = 0.25 mvxy = 158 m/sλ = 0.5 mm
= ~3 s
No buffer gas → PXe ?
pump laser
probe laser
Appl. Phys. B 68 (1999) 93
Appl. Phys. B 68 (1999) 93
