A new measurement of the electron edm. E.A. Hinds. Centre for Cold Matter Imperial College London

Transcription

1 A new measurement of the electron edm E.A. Hinds Centre for Cold Matter Imperial College London Birmingham, 26 October 2011

2 How a point electron gets structure point electron polarisable vacuum with increasingly rich structure at shorter distances: (anti)leptons, (anti)quarks, Higgs (standard model) beyond that: supersymmetric particles?

3 Electric dipole moment (EDM) electron edm spin + - T + - If the electron has an EDM, nature has chosen one of these, breaking T symmetry... CP

4 eedm (e.cm) Multi Higgs Theoretical estimates of eedm MSSM Left - Right other SUSY e selectron The interesting region of sensitivity g e Standard Model Insufficient CP to make universe of matter 4

5 The magnetic moment problem Suppose d e = 5 x e.cm (the region to explore) = 3 x Debye E In a field of 10kV/cm d e E ~ _ 1 nhz When does m. B B equal this? B ~ _ 1 fg d e This is very small electron 5

6 A clever solution amplification For more details, see E. A. H. Physica Scripta T70, 34 (1997) (Sandars 1964) E hd e Interaction energy electric field -d e he F P Polarization factor atom or molecule containing electron Structure-dependent relativistic factor Z 3 6

7 Effective field he (GV/cm) Our experiment uses a molecule YbF GV/cm Amplification in YbF Applied field E (kv/cm) EDM interaction energy is a million times larger (mhz) needs ng stray B field control 7

8 The lowest two levels of YbF X 2 S + (N = 0,v = 0) E F= > +1 > + - +d e he -d e he 170 MHz F=0 0 > Goal: measure the splitting 2d e he to ~1mHz 8

9 Fluorescence How it is done PMT Ch 15 Cold Molecules, eds. Krems, Stwalley and Friedrich, (CRC Press 2009) rf pulse B HV+ Pulsed YbF beam HV- Probe A-X Q(0) F=0 Pump A-X Q(0) F=1 1.0 F=1 F=

10 Detector count rate Measuring the edm Interferometer phase f = 2(mB - + d e he)t/h E -E d e -B B Applied magnetic field 10

11 Modulate everything ±E ±B ± B ±rf1f ±rf2f ±rf1a ±rf2a ±rff ±laser f spin interferometer signal Generalisation of phase-sensitive detection 9 switches: 512 possible correlations Switch periodically on short timescale but randomly on long timescale. Measure all 512 correlations. 11

12 ** 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),

13 Measuring the other 511 correlations fringe slope calibration beam intensity f-switch changes rf amplitude E drift E asymmetry E asymmetry inexact π pulse correlation mean mean/ Nearly all are zero (as they should be)! 13

14 The only systematic error correction rf detuning from resonance makes a (small) interferometer phase shift We measure this by the {rf1f.b} and {rf2f.b} correlations they are both ~ 100 nrad/hz Electric field reversal changes magnitude of E (slightly) causing a Stark shift We measure this by the {rf1f.e} and {rf2f.e} correlations Together false EDM We measure and correct: (+5.5 ± 1.1) e.cm. 14

15 EDM Magnetic field noise B fluctuations have some component synchronous with E reversal: EDM noise B synchronous with E reversal We measure and correct: (-0.3 ± 1.7) e.cm.

16 6194 measurements (~6 min each) at 10 kv/cm EDM (10-25 e.cm) million beam shots Distribution of edm/ edm Gaussian distribution bootstrap method determines distribution 68% confidence level?? ± e.cm includes blind offset 16

17 Current status Previous result - Tl atoms Regan et al. (PRL 2002) Nataraj et al. (PRL 2011) Dzuba/Flambaum (PRL 2009) d e < e.cm with 90% confidence New result YbF Hudson et al. (Nature 2011) d e = ( ) e.cm 68% statistical systematic - limited by statistical noise d e < e.cm with 90% confidence 17

18 eedm (e.cm) Multi Higgs Left - Right MSSM other SUSY New excluded region d e < 1 x e.cm We are ready to explore this region (if funded) Standard Model 18

19 New cryogenic buffer gas source of YbF Yb+AlF 3 target 3K He gas cell YbF beam YAG ablation laser 15 more molecules/pulse 3 longer interaction time (slower beam) => 10 better signal:noise ratio => access to mid e.cm range 19

20 Current status of EDMs d e.cm d(muon) neutron: electron: YbF Multi Higgs Left-Right MSSM d(proton) d(neutron) d(electron)

21 Summary e- EDM is a direct probe of physics beyond SM specifically probes CP violation (how come we re here?) absence of EDM suggests no min. supersymmetry Atto-eV molecular spectroscopy tells us about TeV particle physics!

22 EDM Group Members Jony Hudson Ben Sauer EAH Mike Tarbutt Joe Smallman Dhiren Kara 22