Workshop on nEDM Experimental Tecniques, Oct. 11-13, 2012, ORNL
129Xe
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)
nEDM measurements
with 129Xe comagnetometer
EDM cell
~0.5 nHz
n
νn = (2μnB ± 2dnE)/h
= ~29 Hz
νXe= (2μXeB ± 2dXeE)/h
B E+ E–
= ~12 Hz
129Xe
B = 1μT
E = 10 kV/cm
γn
dn– γ
dXe
Xe
~10–28 e･cm
(νn/νXe)E+
(νn/νXe)E–
1
≒1+4
hνXe
γXe
γn
~10–11
+(0.7±3.3)x10–27 e･cm
dmeasE
Rosemberry & Chupp
PRL86(2001)22
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
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
Larmor precession time TL = 2π/ω0 ~40 ms
dfXe = ~0.9 x 10–28 ecm
cf. dfHg = ~5 x 10–26 ecm
B0 = 2 µT
∂B0z/∂z = 2 nT/m
R = 0.25 m
vxy = 240 m/s@300K
λ = 0.7 mm
129
Xe 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
• 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
van der Waals molecule
Optical pumping
Effect of N2 buffer gas
Plarization of Rb atoms
Polarization of 129Xe nuclei
N2
N2
Xe + N2 + Rb
Ruth et al., Appl. Phys. B 68 (1999) 93
N2
Rosenberry et al., PRA75(2007)023401
Buffer gas N2:
reduce absorption of
de-exciting unpolarized
photons
Plan of 129Xe magnetometer
T2 > ~100 s
EDM cell (Xe: 7 mTorr)
B
V±
probe laser
External cell:
detector
129Xe
polarize 129Xe
Total amount of Xe gas:
〜20 liter (EDM cell + UCN guide)
& Rb
EDM cell
Xe: 7 mTorr (2.5 x 1014 cm-3)
pump laser
UCN guide
External cell: 7 Torr / 20 cm3
No buffer gas (N2)
in EDM cell
Freeze-pump-thaw separation
N2 free
Xe, N2
Rb
probe
laser
Appl. Phys. B 68 (1999) 93
pump laser
Xe N2
LN2
pump
・ Xe + N2 mixture in polarizing cell
・ Solidify Xe
・ Evacuate N2 gas
・ Transport polarized 129Xe into
EDM cell
Appl. Phys. B 68 (1999) 93
Rb-K mixture → 21Ne polarization x 10
pump laser
probe laser
129Xe
nuclear spin relaxation 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)
∝ R4/D x |∇B|2
1/T2 = 1/T1 + 1/T2,field
~ 1/(several h)
∝ p–1
[Gemmel et al., EPJ D57(2010)303]
~10 pT/cm
Measurement of PXe, T1
AFP-NMR
cell
RFcoil
B0
B1
B0 coil
Pickup coil
Proton NMR (H2O)
νL(proton) = 48 kHz@11.2 G
Lock-in amp. out
5s
B0
Ti-sapphire & Ar laser
Rb & Xe transfer system
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)
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-Xe vdW
γse; Rb-Xe spin exchange rate
)
Γsd = γXe-Rb[Xe] + γRb-Rb[Rb] + γN2-Rb[N2] = 1.2 x 103 s–1
24
1100
γse = γXe-Rb[Rb] = 0.13
s–1
33
[Wagshul & Chupp, RRA49(1994)3854]
[Cates et al., PRA45(1992)4631]
Polarize 129Xe nuclear spin
Optical pumping
5P1/2
σ+
794.7 nm
Rb
129Xe
σ+
λ = 794.7 nm
5S1/2
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
PXe ≈ PRb (1 + Γ/γse
)–1
(
Γ; 129Xe relaxation rate except γse
γse; Rb-Xe spin exchange rate
)
)
129Xe
magnetometer
129Xe
129Xe
（90° pulse）
B
B
Measure νXe
during Ramsey resonance
Polarize 129Xe
before storing UCN
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
Observation of 129Xe spin precession in the EDM cell
Bo
2.5×1016/liter 129Xe
μ = -3.9239×10-27 J/T
μ
EDM cell
We need to develop
SQUID 1fT, 5μΦ0/√Hz
vibration?
SERF Cs magnetometer
vibration small effect
SQUID or SERF or NMOR
S = 0.01 m2
We have experience of Xe
polarization by means of spin
exchange optical pumping.
B 129Xe magnetization
= μ0/4π (3r(μ∙r) - μr2)/r5
= 0.98×10-14 T at r = 0.1 m
If 50% polarization,
p =7x 10-3 Torr, V =3 litters,
B = 150 fT
Φ = 0.047 Φ0 cos(ω0t)
Φ0 = h/2e
= 2.067833667×10-15 Tm2
PRA75(2007)023401
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 ?
Appl. Phys. B 68 (1999) 93
Appl. Phys. B 68 (1999) 93