129 xe magnetometry for kek-rcnp neutron edm measurements m. mihara, k. matsuta (osaka univ.) y....

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

Proton NMR (H2O)

Lock-in amp. out

B0

5 s

νL(proton) = 48 kHz@11.2 G

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