Probing the electron edm with cold molecules E.A. Hinds Columbus Ohio, 23 June, 2010 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 an electron gets structure - point electron

electron spin + - edm Electric dipole moment (EDM)

Left - Right MSSM  ~  Multi Higgs MSSM  ~ eEDM (e.cm) Our experiment on YbF molecules explores this region Standard Model d e < 1.6 x e.cm Commins (2002) Excluded region (Tl atomic beam) Deb.

The magnetic moment problem Suppose d e = 5 x e.cm (the region we explore) In a field of 10kV/cm d e.E _ 1 nHz ~ When does  B. B equal this ? B _ 1 fG ~ It seems impossible to control B at this level especially when applying a large E field

A clever solution E electric field de de  amplification atom or molecule containing electron (Sandars) For more details, see E. A. H. Physica Scripta T70, 34 (1997) Interaction energy -d e  E  F P F P Polarization factor Structure-dependent relativistic factor ~ 10 (Z/80) 3 GV/cm

Our experiment uses a molecule – YbF  EDM interaction energy is a million times larger (mHz)  mHz energy now “only” requires nG stray field control Amplification in YbF 16 GV/cm

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

Fluorescence Time of flight (ms) Time-of-flight profile How it is done Pulsed YbF beam Pump A-X Q(0) F=1 Probe A-X Q(0) F=1 PMT 3K beam F=1 F=0 rf pulse B HV+ HV- Scanning the B-field B (nT) Ch 15 Cold Molecules, eds. Krems, Stwalley and Friedrich, (CRC Press 2009)

Measuring the edm Applied magnetic field Detector count rate B0B0 -E E Interferometer phase  = 2(  B + d e  E)  /  Interferometer phase  = 2(  B)  /  -  d e -B 0

Modulate everything Generalisation of phase-sensitive detection Switch periodically on short timescale but randomly on long timescale. Sequence chosen to minimize noise. Measure all 512 correlations. ±E ±B ±B±B ±rf2f ±rf1f ±rf2a ±rf1a ±laser f ±rf  spin interferometer signal 9 switches: 512 possible correlations

7 Non-zero correlations 504 correlations should be zero and they are! correlationmean  mean/   fringe slope calibration  beam intensity   -switch changes rf amplitude  E drift  E asymmetry  inexact π pulse We don’t look at the last one (EDM).

** Don’t look at the mean edm ** We don’t know what result to expect. Still, to avoid inadvert 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.

mean EDM ( e.cm) 7381 measurements (~6 min each) at 11.6 kV/cm mean EDM ( e.cm) 1440 measurements (~6 min each) at 3.3 kV/cm

Initial edm results and std. error -147± 5 × e.cm mean-1010 ( e.cm) edm distribution 11.6 kV/cm Blind results includes blind offset mean-2020 ( e.cm) edm distribution 3.3 kV/cm -144±22 × e.cm with same offset

Two systematic error corrections Magnetic field noise B fluctuations synchronous with E reversal produce false EDM. We measure and correct: (-2.2 ± 1.6) × e.cm. Electric field asymmetry “Reversal” changes magnitude of E (slightly) This induces a false EDM We measure and correct: (+0.4 ± 0.4) × e.cm.

Negligible systematics HV charging current: can magnetize shields  < 0.3 × e.cm  B that reverses with E B. E. Sauer, Dhiren Kara, J. J. Hudson, M. R. Tarbutt, E. A. Hinds “A robust floating nanoammeter”. Rev. Sci. Instr. 79, (2008). HV leakage current: makes B that reverses with E i < 2 nA  < 0.8 × e.cm “A robust floating nanoammeter” Rev. Sci. Instr. 79, (2008). Faraday Discussions, 142, 37 (2009) Changing E direction along beamline   < 0.03 × e.cm  geometric phase

F=0 F=1 sensitive to E (Stark shift) Mapping the E field 3K beam rf pulse B Frequency (MHz) Molecule arrival time PRA (2007) Electric field variation along plates Position along plates (m) gap is constant to ± 90 μm !

One last check... Identical run, but with E reversal disabled 9000 edm measurements (3 months) false edm < 4 × e.cm No systematics observed.

EDM ( e.cm) NO! EDM changes across the pulse One last, last check! PMT Do front and back of pulse measure the same EDM?

What’s going on ??? The edm should not care where it is measured (front or back of pulse) The edm should not care how fast molecules are (570 or 590 m/s) We find that this “chirp” is proportional to (i) detuning of 1 st rf pulse (ii) asymmetry of E reversal Can be corrected, but we’d like a detailed model

Current status Close to a measurement at the level of 4× e.cm Systematics seem under control at this level, but we’d like to understand the chirp. Expect to unveil the result later this summer

New cryogenic buffer gas source of YbF YbF beam YAG ablation laser 3K He gas cell Yb+AlF 3 target Spectroscopy inside: New J.Phys. 11, (2009)

the real thing upper LIF detector lower LIF detector YbF beam

170MHz Q(0) hyperfine splitting Lower PMT Upper PMT molecules /sr/pulse (10 10 ) 170 Beam intensity 174 Q(0) 170 MHz hfs fluorescence spectrum 5  molecules/sr/pulse in N=0 F=1 25  higher intensity than best previous! relative frequency (MHz)

Beam velocity LIF at lower PMT z = 23mm LIF at upper PMT z = 132mm time (ms) v = 150 m/s tuneable by He pressure m/s 700  s

EDM prospects with new source 25  more molecules => 20  better signal:noise ratio Also, ideal source for decelerating or trapping many species and for laser cooling CaF, BaF, SrF to  K. 4  longer interaction time => access to low e.cm range!

Acknowledgements Royal Society EPSRC Euroquam CHIMONO Ben Sauer Jony Hudson Mike Tarbutt Dhiren Kara (Ph..) Joe Smallman (P...) EDM Rich Hendricks Sarah Skoff (Ph..) Nick Bulleid (P...) buffer gas source