Measuring the electron EDM with Cold Molecules E.A. Hinds Warwick, 25 May, 2006 Imperial College London

polarisable vacuum with increasingly rich structure at shorter distances: (anti)leptons, (anti)quarks, Higgs (standard model) beyond that: supersymmetric particles ………? How the 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. beyond std model:

Two motivations to measure EDM EDM is effectively zero in standard model but big enough to measure in non-standard models direct test of physics beyond the standard model (Q: is there a unified theory of all particle interactions?) EDM violates T symmetry Deeply connected to CP violation and the matter-antimatter asymmetry of the universe (Q: why is there more matter than antimatter?)

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

Tl, YbF atom/molecule level CP from particles to atoms (main connections) nuclear level NNNN Schiff moment mercury Higgs SUSY Left/Right Strong CP field theory CP model  GG neutron nucleon level electron/quark level dede dqdcqdqdcq ~

Theoretical consequences of electron EDM d e < 1.6 x e.cm - a direct window onto new physics The “natural” SUSY EDM is too big by 300  CP < 3  ??  > 4 TeV ?? SUSY electron edm ee  selectron 2  meme d e ~ (loop)  sin  CP gaugino CP phase from soft breaking naturally O(1) scale of SUSY breaking naturally ~200 GeV naturally ~  ~ 5  10  25 cm naturally

The magnetic moment problem Suppose d e = 5 x e.cm (just below current limit) In a field of 100kV/cm d e.E _ Hz ~ When does  B. B equal this ? B _ T ! ~ 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 (10 -2 Hz)  mHz energy now “only” requires pT stray field control  Insensitive to B perpendicular to E (suppressed by )  Hence insensitive to motional B (vxE/c 2 =10 4 pT) Amplification in YbF 18 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

Interferometer to measure 2d e  E Pump A-X Q(0) F=1 0 | -1  | +1  | 0  Split | -1 | MHz  pulse Probe A-X Q(0) F=1 0 ? Recombine 170 MHz  pulse Phase difference = 2 (  B + d e  E)T/  E B Source

How we make the YbF beam Pulsed Valve Yb Target YAG laser (25mJ, 10ns) Skimmer 2% SF 6 in 4 bar Ar Pulsed YbF beam A pulsed supersonic jet source The YbF gas pulses are cold (3K), but move rapidly (600 m/s)

The whole experiment Pulsed YbF beam Pump A-X Q(0) F=1 Probe A-X Q(0) F=1 PMT rf split rf recombine Fluorescence Time of flight (  s) Time-of-flight profile rf frequency (MHz) Scanning the rf-frequency Scanning the B-field B (nT) | -1  | +1  | 0 

Fit to YbF interferometer fringes Interference signal (kpps) Magnetic field B (nT) Phase difference = 2(  B+d e  E)T/ 

Magnetic field B (nT) experimental data arrival time (ms) fringe pattern versus time of flight slower moleculesfaster molecules narrower fringes

Measuring the edm Applied magnetic field Detector count rate E B0B0 -E  = 4d e  ET/  -B 0  4d e  ET/ 

100 hrs at 13 kV/cm 80 hrs at 20 kV/cm EDM data taken de ( e.cm)

EDM Data summary  Each dataset has a statistical sensitivity to d e of 7 x e.cm  No result yet - the experiment is incomplete  In particular, measurements of systematic effects

Systematic tests  16 internal machine states – linear combinations flag undesirable asymmetries  4 external machine states  Simultaneous measurement of magnetic fields inside the machine  Simultaneous measurement of leakage currents  Measurements at low electric field in progress  Battery runs etc, etc in progress  Repeat using a control molecule in preparation

ImprovementFactorComment Normalization detector1.5Normalize shot-to-shot variations Higher repetition rate2From 10Hz to 50Hz 2 nd pump laser-beam1.5Access N=2 population Rb-cell magnetometry1Higher sensitivity to magnetic fields Fiber laser1Low maintenance, more stable/reliable Simultaneous YbF/CaF1Better measurement technique Sensitivity level: 2 x e.cm Upgrades in progress Decelerated molecules10Much longer coherence time Sensitivity level: ~ e.cm

 We are building a Stark decelerator for YbF and CaF molecules  Aim to bring molecules to rest and load them into a trap  Perform the edm experiment with slow, trapped molecules: coherence times > 100ms Deceleration and trapping

The eEDM roadmap

Principle of deceleration (0,0) (1,0) For a review see arXiv:physics/ Apr 2006

Our alternating gradient decelerator design high voltage electrodes 21 stages macor insulators

AG focussing in other contexts Optical guiding Ion Trapping

Time of flight (ms) Signal Decelerator off Decelerator on First YbF decelerator result Phys. Rev. Lett. 92, (2004)

Now also CaF

Vision of experiment with trapped molecules supersonic source decelerator preparesplit trap  ~ 1s E B recombineprobe interferometer

Other electron EDM searches Cs atoms Fountain (LBL), Trapped (Penn State), Trapped (Texas) Long coherence time GGG (LANL), GIG (Amherst) Gadolinium Garnets Huge number of electrons Molecules Metastable PbO in cell (Yale) Large effective E field Trapped PbF (Oklahoma) Trapped HBr + ions (JILA) Large effective E field & long coherence time

Neutron EDM expt Room-temperature experiment finished Measurement: d n xE spin precession polarised neutrons in a bottle Hg atom co-magnetometer laser beam New limit: 3.0 x e. cm hep-ex/ Electric field 10kV/cm

CryoEDM starts in October Several other neutron EDM experiments also starting Ultimately 100x more sensitive polarised neutrons moderated in superfluid helium

d(muon)  7× Current status of EDMs d(neutron)  3× d(proton)  6× YbF expt trapped molecules d(electron)  1.6×10 -27

Conclusion Measuring the electron EDM has great potential to elucidate particle physics beyond the standard model matter/antimatter asymmetry of the universe CP violation Some of the most fundamental questions in physics

Rick Bethlem Gerard Meijer Antoine Weis Collaborators Mike Tarbutt Ben Sauer Henry Ashworth Ed Hinds Richard Darnley Jony Hudson Manu Kerrinckx Current Group Members