Transcript Document

スピンエコーの手法を利用し
たフランシウム原子EDMの探
索
全般的な実験の概要
co-magnetometer beamの低速化
独立行政法人理化学研究所
旭応用原子核物理研究室
長谷山智仁
Atomic EDM
2 types of atomic EDM
paramagnetic atom
←
electron EDM
diamagnetic atom ← nuclear Schiff moment ← quark chromo-EDM
and
θQCD
e EDM Enhancement factor: dA /de ～ O (Z3α2)
inner core region : relativistic motion
a strong mixing between opposite-parity states
PRA50,2960(1994)
e EDM の現状と基本相互作用
現在の上限値: |de| < 1.6×10-27 ecm
Berkeley group
205Tl
ground state 6 2 P1/2 ( F=1)
PRL88,071805(2002)
Tl: enhancement factor –585 (Z=81)
PRA50,2960(1994)
Direction of Electric Field
in beam experiment
205Tl-exp.
: E⊥v
requirement: counter-propagating beams
v×E rotation
E // v preferable
voltage accumulation
E // v difficult to apply
PRL88,071805(2002)
対向電場とEDMスピン歳差の積
算
HV
F
v
Atom
E
B
π-flip
GND
電極通過毎にスピンを静磁場で180度回転し
対向電場中でEDMスピン歳差が積算
F
exact matching
EDM
precession
π-flip
Accumulative EDM precessions
mismatching
in
Canceli ng Voltages
GOOD
alternating
π-flips
BAD
one-way
π-flips
longitudinal
view
Longitudinal
E-field
静磁場の回転角は速度分散を持つが
磁場方向も対向させることにより
累積性は保たれる（スピンエコーの手法）
Advantages to use 220Fr
The heaviest alkali atom, Z=87
Large enhancement from e EDM
dFr /de ~ 1×103
F=1/2 hyperfine structure
valence electron 7s1/2 + nuclear spin I=1
d A E  μA B
spin precession
ω
F
Sufficiently long lifetime
τ=39.2 sec
(T1/2 =27.2sec)
RIBF production rate > 5×106 /sec
Total design of RIABR
Dipole Magnet, RF cavity
Electrodes
Neutralization area
Glass nozzle
RI
Stopping
chamber
Yttrium
Spin Selection (1st)
Hexapole Magnet
Detect
or
(QMS)
Spin Selection (2nd)
Quadrupole Magnet
production: slow neutral RI beam
applicable to Francium
for other experiments requiring
high nuclear polarization
Polarize+Analyze
Francium D1 line:
transition between 7s1/2 and 7p1/2 states (λ= 817nm)
Optical Pumping
F=1/2
10s
9s
8p 3/2
8p 1/2
-10000
-15000
8d 5/2
8d 3/2
7d 5/2
7d 3/2
6f
5f
7p 1/2
7p 3/2
-20000
＋3/2
＋1/2
－1/2
－3/2
F=3/2
8s
6d 5/2
6d 3/2
－1/2
＋1/2
D1 line
λ=817nm
7p 1/2
-25000
D2: 718nm
-30000
-35000
mF
－1/2
＋1/2
F=1/2
D1: 817nm
7s
unpol.
9p 3/2
9p 1/2
＋
-5000
σ
Energy level[cm -1]
0
Francium
Calculated by Dzuba et al. Phys.Lett.A95,230(1983)
7s 1/2
F=3/2
220
ionization energy 4.07eV
(2nd smallest of all the atoms)
Rn-like closed shell + 1 valence electron
＋3/2
＋1/2
－1/2
－3/2
Fr
7s1/2 F=1/2 states
mF = +1/2 : stable
mF = -1/2 : unstable → fluorescence
D2 line: used for atomic cooling
Slow Alkali Beams
Longer time for EDM precession
Zeeman technique
Na
Na
saturation intensity (Fr D2-line)
I0 
PRA55,605(1997)
ω
 2.67 mW/cm 2
12π c
3
0
2
２-D Optical Molasses to reduce transverse momentum
Doppler Limit
8.3cm/s
6Li
co-magnetometer
Stable alkali with nuclear spin I=1
thermal atomic beam: available
similar configuration of angular momentum
Atomic magnetic moment: close to 220Fr
relative difference: O(10-3)
Negligible EDM
dLi /dFr ~ 4×10-6
trajectory combination onto 220Fr-path
thermal Li-beam source
Ext.Cav. Diode Laser system
実験装置図
Deceleration of 6Li beam
with Zeeman compensation technique
thermal 6Li atomic beam
low-velocity component:
too tiny a portion….
V el oci ty Di s ti buti on
7.0E-4
300℃
400℃
5.0E-4 500℃
6.0E-4
4.0E-4
3.0E-4
2.0E-4
Deceleration is
Required!
Head-on collisions with photons
a deceleration with a single laser
1.0E-4
Velocity[m/s]
0.0E+0
0
500
1000
1500
2000
Basic concept of the deceleration
resonance with
applied magnetic field
atoms
entering with
high velocity
cancellation
Doppler shift ⇔ Zeeman shift
atoms entering with
low velocity
position
2500
3000
Momentum transfer with photon
1-photon momentum
1.848eV/c
0.099m/s
Laser
absorption
Fluorescence
(random direction)
Atomic
momentum
6
Li
atom
recoil on
induced emission
laser
beam
Fluorescent
recoil
Radiative lifetime (2p3/2) 26.9ns
Momentum : 1.87×104eV/c
Doppler shift : 1.49GHz
Compensating field : 0.1065T
(for v=1000m/s)
successive scatterings of ~104 photons
cycling transition for deceleration
D2 line (2s1/2→ 2p3/2) 671.0nm (446.8THz, 1.848eV)
(F, F’) = (3/2, 5/2) circular polarization
Although hyperfine transitions, (F, F’) = (3/2, ＊) are irresolvable,
circular polarization allows only (3/2, 5/2) for successive transitions.
6Li
Deceleration Rate
(Zeeman shift included)
Light absorption and scattering rate
p 
s0  / 2
1  s0  [2(   D ) / ]2
FWHM  Γ 1  s0
 : laser detuning from resonance
 D : Doppler shift
 2 π  5.92MHz (equiv. 3.97m/s capture limit)
ω30
s0 I I s , I s 
 2.56 mW/cm 2
2
12 π c
220Fr
power-broadened line width
7.57MHz, 5.44m/s
2.67mW/cm2
4 10 7
maximum deceleration (s0→∞)
0 
2
 1.84 106 m s
2Mc
220Fr
6.01×104m/s2
field, gradient and laser power


2
2
2

dB amax s0  0 
2.085 10 T /m 

  s0  
B

 1
dB
dz 1  s0   B c 


B


dz


This condition should NOT be satisfied at the exit.
z
fact 1
fact 3
fact 10
fact 30
-1
Photon Scattering Rate[s ]
amax 
sat.
sat.
sat.
sat.
-2
B = 5.33 x 10 T
220Fr
3 10 7
2 10 7
1 10 7
1
5.952×10-4 T2 / m
0
480
490
500
velocity [m/s]
510
520
magnet
inhomogeneous
solenoids
6Li
beam
exit
6Li
beam
entrance
MAX 0.12T
Profile coil:
field gradient
Bias coil:
uniform shift
Extraction coils: sudden drop
MAX 0.01T
MAX 0.02T
Example of parameter setting
929m/s→ 200m/s
additional slowering
as required
6
Li
atom
Laser
まとめ
フランシウム原子のＥＤＭ測定
v×E systematicsを無くす為、縦方向電場での測定をする。
スピンエコーの手法による対向電場中でのスピン歳差角の蓄積。
低速中性Fr原子ビームの生成、ゼーマン減速法による低速化、
Optical pumpingとfluorescence測定によるスピン歳差角の測定、
6Li co-magnetometerの使用……..。
6Li原子ビームの低速化装置の設計・製作