Atomic parity violation in ytterbium
Dmitry Budker
University of California, Berkeley
Nuclear Science Division, LBNL
PREX Workshop
JLAB, August 16-18, 2008
http://socrates.berkeley.edu/~budker/
Outline
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Motivation
The Yb system
Measurement principle
Apparatus
Preliminary parity-violation results
Experimental issues
Outlook (Yb and Dy)
2
Motivation
 Verification of large predicted atomic PV effect
(x100 Cs; DeMille, Kozlov et al, Das et al)
 Isotopic ratios and neutron distributions
(6 stable isotopes; N=8)
 Nuclear spin-dependent PV – anapole moments
(valence neutrons)
3
Isotopic ratios and neutron distributions
• Atomic PV calculation errors cancel in isotopic ratios
Dzuba, Flambaum, and Khriplovich, Z. Phys. D 1, 243
(1986)
• But enhanced sensitivity to the neutron distribution rn(r)
Fortson, Pang, Wilets, PRL 65, 2857 (1990)
• Atomic PV  Neutron distributions
• For 170Yb-176Yb, QW  -100;
QW(Standard Model)  6
QW(Neutron Skin)  3
4
Isotopic ratios and neutron distributions:
new development (ArXiv)
• Neutron-skin effects in different isotopes are correlated
5
Anapole Moments
• 1959 Ya . B. Zel’dovich, V. G. Vaks
AM first introduced
• 1980-84 V.V. Flambaum, I.B. Khriplovich &
O.P. Sushkov
Nuclear AM detectable in atoms
E.N.Fortson and co-workers
• 1995
Tl AM – small…
C. E. Wieman and co-workers
• 1997
Cs AM detected !
PNC within nucleus !
probe of weak meson couplings
6
Atomic Yb: energy levels and transitions
+5d6p
PNC amplitude: 10-9e·a0
DeMille (1995)
|M1|10-4 μB
J.E. Stalnaker, et al, PRA
66(3), 31403 (2002)
β2·10-8 ea0/(V/cm)
C.J. Bowers et al, PRA 59(5), 3513
(1999); J.E. Stalnaker et al, PRA 73,
043416 (2006)
7
Stark-PV-interference
Geometries and invariants:
  E  B
  B  E    B 
8
PV effect on line shapes:
even isotopes
E  (E,0,0)
ε  (0,sinθ,cos θ)
R 0   2 E 2 sin 2 θ  2 E sin θ cos θ
1
R 
168,170,174,176Yb
 2 E2
2
cos2 θ   E sin θ cos θ
or θ
PV-Stark
interference
terms
9
PV effect on line shapes:
odd isotopes
E  (E,0,0)
ε  (0,sinθ,cos θ)
R
β2FF E 2

(4sin 2θ  cos2 θ)  β FFE  sin θcos θ
6
β2FF E 2

cos2 θ  β FF E  sin θcos θ
2
center
R side
     I  J  NSD
NSD~10-11 ea0 for
odd Yb isotopes
=10-9 ea0
` must be
measured with
0.1% accuracy
10
The Yb PNC Experiment
Electric and magnetic fields define handedness


Rotational Invariant:   B E    B

11
Optical system and control electronics
Light powers:
Ar+: 15W
Ti:Sapp (816 nm): 1 W
Doubler (408 nm): 50 mW
PBC:
Confocal design, 25 cm;
Finesse ~10,000
(upgrading to 40000 ??)
Locking:
Pound-Drever-Hall
technique
12
Typical signal
• 174Yb resonance split by B70 G; E=3 kV/cm
• Expected PV asymmetry: ~ 2·10-4/ E/(kV/cm)
• Asymmetric lineshape ← AC Stark effect
13
Atoms in electric field: the Stark effect
or LoSurdo phenomenon
Johannes Stark (1874-1957)
Nazi
Fascist
14
Reversals and pseudo-reversals
• E-field reversal (14 ms: 70-Hz modulation)
• Lineshape scan (200 ms/point x 100 pts/lineshape = 40 s)
• B-field reversal (every few minutes)
• Polarization angle (occasionally)
• E-field magnitude
• B-field magnitude
• Angle magnitude
For θ=/4→
15
Reversals and pseudo-reversals
16
Statistical Sensitivity
• With parameters presently achieved, the shot noise limit is:
S
   T ( s)
 N  PV
• 10 hrs should correspond to a 0.5% measurement…
17
But there are some problems:
• Photo-induced PBC mirror deterioration in vacuum
• Slow drifts
• Technical noise (above shot-noise)
• Stray electric fields (~ up to a few V/cm)
18
Power-buildup cavity design and characterization
C. J. Hood, H. J. Kimble, J. Ye. PRA 64, 2001
2
F
T1  T2  L1  L2
Ptrans
 F 
 T1T2 

 Pin
 2 
2
0.20
Ringdown
spectroscopy
PBC transmission [V]
=2.16 s F=9253
0.15
0.10
=1.74 s F=7454
0.05
=1.33 s F=5698
0.00
-10
-5
0
Time [s]
5
10
19
Power-buildup cavity design and characterization:
mirrors
REO set1
l=408 nm
REO set2
l=408 nm
ATF
l=408 nm
Boulder expt
l=540 nm
Transmission
320 ppm
45; 23 ppm
130 ppm
40; 13
S+A losses
120 ppm
213; 83 ppm
800 ppm*
<1 ppm
* Substrates were provided by Rainbow Research Optics, Inc, Denver, CO
Finesse of 29000 seen with REO mirrors
Photodegradation is still a problem
Locking electronics needs work
20
The 70-Hz E-modulation scheme
to avoid low-frequency noise and drift issues
120
2d harmonic signal
fit
Signal Amplitude [nA]
100
80
60
40
20
0
-60
-40
-20
0
20
1.8 integration
20-s
60
1st harmonic signal
fit
PNC line shape (x10)
1.6
Signal Amplitude [nA]
40
1.4
1.2
1.0
0.8
Due to bias ex  25 V/cm
0.6
0.4
0.2
0.0
-0.2
-60
-40
-20
0
f [MHz]
20
40
60
Different pattern
and polarization
21
dependence for PV
Present status: PV results
0.25
0.20
Im(/) [V/cm]
0.15
0.10
78(22) mV/cm
0.05
0.00
-0.05
1
2
3
4
5
6
Run number
• About 14 hours of data collection
• Limited by shot noise and stray fields → to be improved
• Systematics checks in progress
22
Present status: systematics
2(bx ey)/(B0 Edc)
2(bx ez)/(B0 Edc)
0.025
Background
0.020
0.015
Asymmetry
0.010
0.005
0.000
-0.005
-0.010
-0.015
-0.020
1
2
3
4
5
6
Run
Average stray ex-field: 150 mV/cm
23
Progress towards measuring PV in Yb
Completed Work
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
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

Lifetime Measurements
General Spectroscopy (hyperfine shifts, isotope shifts)
dc Stark Shift Measurements
Stark-Induced Amplitude (β): 2 independent measurements
M1 Measurement (Stark-M1 interference)
ac Stark shifts measured
Almost there
 Verification of PV enhancement
And then…
 PV in odd isotopes: NSD PV, Anapole Moments
 PV in a string of isotopes; neutron distributions, …
24
Yb: the team
K. Tsigutkin
post-doc
A. Family
undergrad
J. E. Stalnaker
grad. student → prof. @ Oberlin
D. Dounas-Frazer
new grad.student
25
The parity violation experiment in Dy
evolved into…
26
Phys. Rev. Lett. 98, 040801 (2007)
a/a  (-2.9 ± 2.6mostly syst) x 10-15 yr-1
27
a
18
~ 10 / yr
a

PV with mHz sensitivity
Status: setting up
28