the edm of electrons, neutrons, & atoms
TRANSCRIPT
A new measurement of the electron edm
E.A. Hinds
Birmingham, 26 October 2011
Centre for Cold Matter
Imperial College London
+ +
+ +
polarisable vacuum with increasingly rich structure at shorter distances:
(anti)leptons, (anti)quarks, Higgs (standard model) beyond that: supersymmetric particles ………?
How a point electron gets structure
-
point electron
electron spin
+ -
edm
Electric dipole moment (EDM)
T + -
If the electron has an EDM, nature has chosen one of these,
breaking T symmetry . . . CP
Left -Right
other SUSY
Multi Higgs
MSSM 10-24
10-22
10-26
10-28
10-30
10-32
10-34
10-36
eEDM (e.cm)
Standard Model 4
The interesting region of sensitivity
Theoretical estimates of eEDM
Insufficient CP
to make universe
of matter
e e
g selectron
electron
de
Suppose de = 5 x 10-28 e.cm (the region to explore)
In a field of 10kV/cm de E _ 1 nHz ~
This is very small
E
= 3 x 10-19 Debye
When does mB.B equal this ? B _ 1 fG ~
The magnetic moment problem
5
A clever solution
E
electric field
hde
amplification
atom or molecule containing electron
(Sandars 1964)
For more details, see E. A. H. Physica Scripta T70, 34 (1997)
Interaction energy
-de hE•
F P Polarization factor
Structure-dependent relativistic factor
Z3
6
Our experiment uses a molecule – YbF
EDM interaction energy is a million times larger (mHz)
needs nG stray B field control
0
5
10
15
20
0 10 20 30
Applied field E (kV/cm)
Eff
ecti
ve f
ield
hE
(G
V/c
m)
Amplification in YbF
16 GV/cm
7
| -1 > | +1 >
| 0 >
The lowest two levels of YbF
Goal: measure the splitting 2dehE to ~1mHz
F=1
F=0
E
-dehE
+dehE
+
-
+
-
X2S+ (N = 0,v = 0)
170 MHz
8
Pulsed YbF beam
Pump A-X Q(0) F=1
Probe A-X Q(0) F=0
PMT
F=1
F=0
rf pulse
B HV+
HV-
How it is done
Ch 15 Cold Molecules, eds. Krems, Stwalley and Friedrich, (CRC Press 2009)
1
1.0
0.0
Flu
ore
scen
ce
Measuring the edm
Applied magnetic field
Det
ecto
r co
un
t ra
te
B
-E E
Interferometer phase f = 2(mB + dehE)t/h -
de
-B
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Modulate everything
• Generalisation of phase-sensitive detection
• Switch periodically on short timescale
but randomly on long timescale.
• Measure all 512 correlations.
±E ±B
±B
±rf2f ±rf1f
±rf2a ±rf1a
±laser f ±rff
spin interferometer
signal
9 switches: 512 possible correlations
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** Don’t look at the mean edm **
• We don’t know what result to expect.
• Still, to avoid inadvertent bias we hide the mean edm.
• A random blind offset is added that only the computer knows.
• More important than you might think. – e.g. Jeng, Am. J. Phys. 74 (7), 2006.
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Measuring the other 511 correlations
correlation mean mean/
fringe slope calibration beam intensity f-switch changes rf amplitude E drift
E asymmetry E asymmetry inexact π pulse
• Nearly all are zero (as they should be) !
13
The only systematic error correction
• Electric field “reversal” changes magnitude of E (slightly) causing a Stark shift
We measure and correct: (+5.5 ± 1.1) ×10-28 e.cm.
• rf detuning from resonance
We measure this by the {rf1f.B} and {rf2f.B} correlations they are both ~ 100 nrad/Hz
makes a (small) interferometer phase shift
We measure this by the {rf1f.E} and {rf2f.E} correlations
• Together false EDM
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• Magnetic field noise B fluctuations have some component synchronous
with E reversal:
We measure and correct: (-0.3 ± 1.7) ×10-28 e.cm.
B synchronous with E reversal
ED
M
EDM noise
6194 measurements (~6 min each) at 10 kV/cm.
bootstrap method determines distribution
16 -5 5 0
Gaussian distribution
Distribution of edm/edm
?? ± 5.7 ×10-28 e.cm
includes blind offset
68% confidence level
2
1
0
-1
-2
EDM (10-25 e.cm)
25 million beam shots
Current status
de = (-2.4 5.7 1.5) ×10-28 e.cm
68% statistical systematic - limited by statistical noise
de < 1 × 10-27 e.cm with 90% confidence
• Previous result - Tl atoms
de < 2.0 × 10-27 e.cm with 90% confidence
• New result – YbF – Hudson et al. (Nature 2011)
Regan et al. (PRL 2002) Nataraj et al. (PRL 2011) Dzuba/Flambaum (PRL 2009)
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Left -Right other
SUSY
Multi Higgs
MSSM 10-24
10-22
10-26
10-28
10-30
10-32
10-34
10-36
eEDM (e.cm)
We are ready to explore this region
(if funded)
Standard Model
de < 1 x 10-27 e.cm
New excluded region
18
New cryogenic buffer gas source of YbF
YbF beam
YAG ablation laser
3K He gas cell
Yb+AlF3
target
19
15 more molecules/pulse
=> 10 better signal:noise ratio
3 longer interaction time (slower beam)
=> access to mid 10-29 e.cm range
d(muon) 7×10-19
10-20
10-22
10-24
d e.cm
1960 1970 1980 1990 2000 2010 2020 2030
Current status of EDMs
d(proton) 5×10-24
d(electron) 1×10-27
neutron:
Left-Right
MSSM
Multi
Higgs
electron:
10-28
10-29
d(neutron) 3×10-26 10-26
YbF
Summary e- EDM is a direct probe of physics beyond SM
Atto-eV molecular spectroscopy tells us about TeV particle physics!
specifically probes CP violation (how come we’re here?)
absence of EDM suggests no min. supersymmetry
Mike Tarbutt Ben Sauer
EDM Group Members
Jony Hudson EAH
Dhiren Kara Joe Smallman
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