Search for the electron’s EDM
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Transcript of Search for the electron’s EDM
Search for the electron’s EDM
E.A. Hinds
PCPV, Mahabaleshwar, 22 February 2013
Centre for Cold MatterImperial College London
Is the electron round?
+ +
++
polarisable vacuum with increasinglyrich structure at shorter distances:
(anti)leptons, (anti)quarks, Higgs (standard model)beyond that: supersymmetric particles ………?
How a point electron gets structure
-
point electron
electronspin
+-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 interestingregion of sensitivity
Theoretical estimates of eEDM
Insufficient CPto make universeof matter
e e
gselectron
electron
de
Suppose de = 5 x 10-28 e.cm(the region we explore)
In a field of 10kV/cm de E _ 1 nHz ~
This is very small
E
= 1 x 10-19 e.a0
When does mB.B equal this ?B _ 1 fG~
The magnetic moment problem
5
A clever solution
E
electric field
de amplification
atom or molecule containing electron
(Sandars)
For more details, see E. A. H. Physica Scripta T70, 34 (1997)
Interaction energy -de E•
F P Polarization factor
Structure-dependent
relativistic factor Z3
6
Our experiment uses a polar molecule – YbF
EDM interaction energy is a million times larger (mHz) needs “only” nG stray B field control
0
5
10
15
20
0 10 20 30
Applied field E (kV/cm)
Effe
ctiv
e fi
eld
E
(GV
/cm
)Amplification in YbF
15 GV/cm
7
Pulsed YbF beam
Pumplaser
Probelaser
PMT
3K beamrf pulse
HV+
HV-
How it is donerf pulse
B
Measuring the edm
Applied magnetic field
Det
ecto
r co
unt r
ate
B
-EE
Interferometer phase f = 2(mB + deE)t/h-
de
-B
9
Modulate everything
• Generalisation of phase-sensitive detection
• Measure all 512 correlations.• E·B correlation gives EDM signal
±E±B
±B±rf2f±rf1f
±rf2a±rf1a
±laser f±rff
spin interferometer signal
9 switches:
512 possible correlations
10
** 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.
• An offset is added that only the computer knows.
• More important than you might think.– e.g. Jeng, Am. J. Phys. 74 (7), 2006. 11
2011 Data:6194 measurements (~6 min each) at 10 kV/cm.
bootstrap methoddeterminesprobability distribution
12-5 50
Gaussiandistribution
Distribution ofedm/edm
2
1
0
-1
-2
EDM (10-25 e.cm)
25 million beam shots
Measuring the other 511 correlationscorrelation mean mean/
fringe slope calibrationbeam intensityf-switch changes rf amplitudeE drift
E asymmetry E asymmetryinexact π pulse
• The rest are zero (as they should be) !
13
• Only now remove blind from EDM
Current status
de = (-2.4 5.7 1.5) ×10-28 e.cm
68% statisticalsystematic - limited by statistical noise
de < 1 × 10-27 e.cm with 90% confidence
• Previous result - Tl atoms
de < 1.6 × 10-27 e.cm with 90% confidence
• 2011 result – YbF Hudson et al. (Nature 2011)
Regan et al. (PRL 2002)Dzuba/Flambaum (PRL 2009)Nataraj et al. (PRL 2011)
14
Kara et al. NJP 14, 103051 (2012)
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 starting toexplore this region
Standard Model
de < 1 x 10-27 e.cm
New excluded region
15
How we will improvePhase 1 Small upgrades: 3 x improvement
– in progressPhase 2 Cryogenic source of YbF
– almost ready
Phase 3 Laser-cooled molecular fountain – being developed
16
Phase 1:
Now making a210-28 e.cm
EDM measurement
• Longer interferometer• Lower background
2.5sensitivity
6543210
Stray Bx
E direction
E magnitudeStray By
Pump pol.Probe pol.
Pump freqProbe freq
F=1 detect
Max uncertainty (10-29 e.cm)
Systematics emphasised total < 10-28 e.cm
Defects emphasised
Phase 2 - cryogenic buffer gas source of YbF
YbF beam
YAGablationlaser3K He gas cell
Yb+AlF3target
18
Cryogenic beam spectrum
Rotational temperature: 4 ± 1 K Translational temperature: 5 ± 1 K
19
10 more molecules/pulse
=> 10 better EDM signal:noise ratio4 longer interaction time (slower beam)
=> access to mid 10-29 e.cm range
3K beamsource
laser cooling
1/2 sec flight time (instead of 1/2 ms)
Phase 3 – a molecular fountain
Laser cooling
=> 610-31 e.cm statistical (in 8 hrs)
detectionguide
HV+ HV-
He
rf pulse
20Tarbutt et al. arXiv:1302.2870
Other eEDM experiments in preparation
WC : 3Δ1 ground stateLeanhardt group, Michigan
Acme collaboration, Harvard/Yale
ThO : 3Δ1 metastable
HfF+ : 3Δ1 ground stateCornel Group JILA
Atom experiments in preparationCs in optical lattice: Weiss group, Penn State (next year?)
Heinzen group, Texas (2 years?)Fr in a MOT: Tohoku/Osaka (starting 2014)
d(muon) < 1.9×10-19
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
MultiHiggs
electron:
10-28
10-29
d(neutron) < 3×10-2610-26
YbF
22
Summary
Atto-eV molecular spectroscopytells us about TeV particle physics:
specifically probes CP violation
(how come we’re here?)
23the electron is too round for MSSM!
e- EDM is a direct probe of physics beyond SM
Left -Right other
SUSY
Multi Higgs
MSSM 10-24
10-22
10-26
10-28
10-30
we see a way to reach <10-30
Thanks to my colleagues...
EDM measurement:Joe Smallman
Jack DevlinDhiren Kara
Buffer gas cooling:Sarah SkoffNick Bulleid
Rich Hendricks
Laser cooling:Thom Wall
Aki MatsushimaValentina Zhelyazkova
Anne Cournol
Jony Hudson Ben SauerMike Tarbutt