Searching for the electron’s EDM Is the electron round? Searching for the electron’s EDM E.A. Hinds Centre for Cold Matter Imperial College London Les Houches, 24 September 2014

How a point electron gets structure + 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 ………?

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

Theoretical estimates of eEDM eEDM (e.cm) 10-22 e g selectron 10-24 Left -Right other SUSY Multi Higgs MSSM The interesting region of sensitivity 10-26 10-28 10-30 10-32 Insufficient CP to make universe of matter 10-34 10-36 Standard Model 4

The magnetic moment problem Suppose de = 5 x 10-28 e.cm (the region to explore) = 1 x 10-19 e.a0 In a field of 10kV/cm de   E _ 1 nHz ~ E When does mB.B equal this ? B _ 1 fG ~ de This is very small electron 5

Structure-dependent relativistic factor  Z3 A clever solution de  Sandars amplification atom/molecule containing electron E electric field energy -de E• F P Polarization factor Structure-dependent relativistic factor  Z3 For more details, see E. A. H. Physica Scripta T70, 34 (1997) 6

Our experiment uses a molecule – YbF Amplification in YbF 15 GV/cm EDM interaction energy is a million times larger (mHz) needs “only” nG stray B field control 7

E The lowest two levels of YbF X2S+ (N = 0,v = 0) -dehE +dehE + - E | -1 > | +1 > F=1 170 MHz | 0 > F=0 Goal: measure the splitting 2dehE to <1mHz 8

How it is done rf pulse sin2f cos2f F=1 F=0 PMT HV+ 3K beam Pulsed YbF Probe A-X Q(0) F=0 PMT Ch 15 Cold Molecules, eds. Krems, Stwalley and Friedrich, (CRC Press 2009) B HV+ rf pulse 3K beam Pulsed YbF beam HV- Pump A-X Q(0) F=1 1.0 0.0 Fluorescence cos2f sin2f F=1 F=0 1

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

Modulate everything spin interferometer ±E ±B ±B ±rf1f ±rf2f ±rf1a signal ±rf2a ±rf ±laser f Generalisation of phase-sensitive detection Measure all 512 correlations. E·B correlation gives EDM signal 9 switches: 512 possible correlations 11

** 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. 12

Measuring the other 511 correlations mean s mean/s fringe slope calibration beam intensity f-switch changes rf amplitude E drift E asymmetry inexact π pulse The rest are zero (as they should be) ! Only now remove blind from EDM 13

2011 Result: Hudson et al. Nature 473, 493 (2011) 6194 measurements (~6 min each) at 10 kV/cm. 2 1 -1 -2 EDM (10-25 e.cm) 25 million beam shots de = (-2.4  5.7  1.5) ×10-28 e.cm systematic - limited by statistical noise 68% statistical Details in Kara et al. NJP 14, 103051 (2012) 14

de = (−2.1 ± 3.7stat ± 2.5syst) × 10−29 (ten x better) arXiv:1310.7534 (October 2013) 3D1 metastable state see Additional reversal (-doublet) helps some systmatics But, signal limited by 2 ms decay lifetime de = (−2.1 ± 3.7stat ± 2.5syst) × 10−29 (ten x better)

eEDM (e.cm) New excluded region MSSM Multi Higgs 10-22 de < 9 x 10-29 e.cm New excluded region 10-24 Left -Right other SUSY Multi Higgs MSSM 10-26 YbF 10-28 ThO We plan to explore this region 10-30 10-32 10-34 10-36 Standard Model 16

How we are improving Phase 1 Small upgrades: 30 x improvement Phase 3 Laser-cooled molecular fountain – being developed How we are improving Phase 1 Small upgrades: 30 x improvement – in progress Phase 2 Cryogenic source: 10 x more again – almost ready 17

Phase 1: Longer interferometer - finer fringes Better magnetic shielding – lower B noise Better field plate structure – higher E and rf control More molecules Better detection efficiency

Getting more molecules to start in N=0, F=0 - A2P1/2 F=0, 1 F=1 F=2+ F=2- F=3 N=2 + F=0 F=1+ F=1- F=2 N=1 - X2S rf mixing (~100 MHz) Microwave mixing (14 GHz) + F=1 N=0 F=0 gives 7 × more molecules

gives 14 × more photons per molecule and 2 × molecules getting better detection by optical cycling - A2P1/2 F=0, 1 F=1 F=2+ F=2- F=3 N=2 + F=0 F=1+ F=1- F=2 N=1 - X2S Move cos2f population up here bring cos2f population back and and detect that too cos2f + N=0 sin2f detect sin2f with closed system gives 14 × more photons per molecule and 2 × molecules

=> access to mid 10-30 e.cm range Phase 2 - cryogenic buffer gas source of YbF YbF beam Yb+AlF3 target YAG ablation laser 3K He gas cell 10  more molecules/pulse 3  slower beam => 10  better EDM signal:noise ratio => access to mid 10-30 e.cm range 21

Phase 3 – a molecular fountain HV+ HV- Laser cooling rf pulse 1/2 sec flight time (instead of 1/2 ms) => 610-31 e.cm statistical (in 8 hrs) detection laser cooling 3K beam source guide He Tarbutt et al. arXiv:1302.2870 22

Current status of EDMs d(muon) < 1.9×10-19 d(proton) < 5×10-24 d e.cm d(muon) < 1.9×10-19 neutron: 10-20 electron: 10-22 Left-Right MSSM Multi Higgs d(proton) < 5×10-24 10-24 d(neutron) < 3×10-26 YbF 10-26 10-28 d(electron) < 9×10-29 ThO 10-29 1960 1970 1980 1990 2000 2010 2020 2030 23

Summary Atto-eV molecular spectroscopy 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 specifically probes CP violation (how come we’re here?) we see a way to reach 10-31 Atto-eV molecular spectroscopy tells us about TeV particle physics: the electron is too round for MSSM! 24

Thanks to my colleagues... Jony Hudson Mike Tarbutt Ben Sauer Laser cooling: Valentina Zhelyazkova Anne Cournol James Almond Jongseok Lim Noah Fitch EDM measurement: Joe Smallman Jack Devlin Dhiren Kara Isabel Rabey Buffer gas cooling: Sarah Skoff Nick Bulleid Rich Hendricks James Bumby