Electron EDM Searches

Transcription

1 Electron EDM Searches Paul Hamilton Yale University INT Workshop Seattle, October 2008

2 Outline Theoretical Motivation General detection method Past and current eedm searches Molecular eedm searches and the PbO* experiment Advantages of molecules Apparatus Results Conclusions

3 An EDM Violates Parity and Time Reversal Symmetries CPT theorem T-violation = CP-violation Standard Model generates through Standard radiative corrections Model can generate d e <10-40 EDM e cm through radiative corrections predict Any observation d e <10-40 of e cm d e 0 is definitive evidence of new physics CP-Violation is required to create matter-antimatter asymmetry in universe. CP violation CP-violation in SM too in small SM to is account too small for matter-antimatter to account for observations. assymetry Any observation de 0 definitive evidence of new physics A window to NEW physics Standard model extensions often include new source of T-violation

4 How does an electron EDM arise? Standard Model Supersymmetry t γ γ W d ~ e t ~ s e e e W ν~ γ b W e e

5 Beyond the SM Electron EDM estimation eedm g-2 The analogous diagram for first-order correction to electron g factor gives g-2 α/π Since m e is the only energy scale we expect the EDM to scale as Which gives an estimate of or d e GeV e cm mx 2

6 eedm Theoretical Predictions

7 Outline Theoretical Motivation General detection method Past and current eedm searches Molecular eedm searches and the PbO* experiment Advantages of molecules Apparatus Results Conclusions

8 General method to detect an EDM ηω=2μβ +2dE -2dE B E Energy level picture: S Figure of shift resolution ηω=2μβ +2dE -2dE de = E τ N& T merit: ( 1/ τ )( S/ N ) coh 1 coh int ω

9 Outline Theoretical Motivation General detection method Past and current eedm searches Molecular eedm searches and the PbO* experiment Advantages of molecules Apparatus Results Conclusions

10 Tl detectors photodiodes Na detectors B Down beam oven Na detectors Tl detectors Beam stop Beam stop Light pipe Collimating slits E-field plates (120 kv/cm) atomic beams Collimating slits Up beam oven Tl reservoir (~700 C) Tl reservoir (~700 C) 378 nm laser beams 590 nm laser beams RF 2 RF nm laser beams 378 nm laser beams Na reservoir (~350 C) Analyzer/ State Selector State Electron of the EDM art limit: B. Regan, E. E electron EDM search: int = 70 MV/cm Na Commins, atoms C. the (low Schmidt, Berkeley Z, L=100 small D. cm DeMille enhancement) T 3 ms Phys. Rev. as Lett. co-magnetometer 88, (2002) Tl beam d experiment Counterpropagating e < e cm (90% c.l.) State Selector/ Analyzer Na reservoir (~350 C) Thermal beam of atomic Tl (Z=81) Efficient laser/rf spin polarization & detection B-field count noise rate rejection ~ 10 9 /s with side-by-side E =120 kv/cm regions (P ~10-3 ) to check systematics vertical beams to cancel (but: little utility in practice) systematic effects from B motional = E v/c (but: complex procedure to null residuals)

11 A new generation of electron EDM searches Group System Advantages Projected gain D. Weiss (Penn St.) Trapped Cs Long coherence ~100 D. Heinzen (Texas) Trapped Cs Long coherence ~100 H. Gould (LBL) Cs fountain Long coherence ~100 L. Hunter (Amherst) GdIG solid Huge S/N 100?, limited by systematic S. Lamoreaux (Yale) GdIG solid Huge S/N 100?-100,000? E. Hinds (Imperial) YbF beam Internal E 10? D. DeMille (Yale) J. Doyle G. Gabrielse (Harvard) PbO* cell ThO beam Int.E+good S/N Int.E+good S/N 2-10? 1000+? E. Cornell (JILA) trapped HfF + Int. E + long T 1000? N. Shafer-Ray (Okla.) trapped PbF Int. E + long T??

12 Electron EDM with cold trapped atoms David Weiss et al. (& similar D. Heinzen et al. ) trapped atoms Cs (Z=55) EDM plus Rb(Z=37) comagnetometer 5 V E~ cm x100 for Cs E int Linear Photodiode Array 10 cm YAG lattice and guide beams Atoms loaded from below Coherence time: T~2-5 s Atom number: N ~2x10 Cs 8 N ~8x10 Rb δd e ~ e cm for both Cs and Rb in ~1 day 9

13 Solid state electron EDM searches 1: B from E magnetometer coil 2: E from B Shapiro Lamoreaux DeMille E V B Sample magnetization M d e E/T Expt: Lamoreaux (Yale) Sample voltage V d e Expt: Hunter (Amherst)

14 Outline Theoretical Motivation General detection method Past and current eedm searches Molecular eedm searches and the PbO* experiment Advantages of molecules Apparatus Results Conclusions

15 A new direction in EDM searches: using molecules to search for d e Extremely large effective E-field with lab-size external field: P ~ 1 E eff ~ V/cm (For atoms, P ~ E ext ~ 100kV/cm) Smaller signals due to thermal distribution over rotational levels (~10-4 ) Molecules with unpaired electron spins are thermodynamically disfavored high temperature chemistry, even smaller signals

16 Addressing some problems with molecules: the metastable a(1)[ 3 Σ + ] state of PbO PbO is thermodynamically stable (routinely purchased and vaporized) a(1) populated via laser excitation (replaces chemistry) a(1) has very small Ω-doublet splitting complete polarization with very small fields (>10 V/cm), equivalent to E ~10 7 V/cm on an atom! can work in vapor cell (MUCH larger density and volume than beam) PbO Cell: Tl Beam: N = nv ~ N = nv ~ 10 8

17 Amplifying the electric field Ε with a polar molecule Pb + Ε ext O Ε int Complete polarization of PbO* achieved with Ε ext ~ 10 V/cm Inside molecule, electron feels internal field Ε int ~ α 2 Z 3 e/a (b) -4.0 (a) V/cm in PbO* (a) Semiempirical: M. Kozlov & D.D., PRL 89, (2002); (b) Ab initio: Petrov, Titov, Isaev, Mosyagin, D.D., PRA 72, (2005).

18 PbO Ω doublet structure Electric field polarizes molecule Zeeman shift splits sublevels EDM shift depends on relative alignment of spin and internal electric field Ω doublet pairs have opposite sign for EDM shift but respond identically to magnetic fields -> internal co-magnetometer d e n gµb + d e E n d e m=-1 m=0 m=+1 B Ω doubling E d e n gµb - d e E n d e

19 The PbO EDM lab.001 km

20 Experimental apparatus a) Magnetic shielding (up to 4 layers) b) Vacuum chamber c) Alumina fiber board insulation d) Quartz oven w/ resistively heated Ta foils e) Alumina vapor cell with YAG windows f) Gold electrodes g) Quartz light pipes h) PMTs i) Microwave horn

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22 Detection Method Quantum beat spectroscopy: Fluorescence modulation frequency equals energy level splitting Doppler free! Current detection method suffers from low contrast and large background due to blackbody radiation from the oven 0.55 ω beat Count Rate (10 11 p.e./s) Contrast Decay from lifetime of metastable state Blackbody background Time (μs) Figure of merit for shift resolution E 1 1 statistical sensitivity: ( 1 T )( SNR) ( c) = E T N c

23 Data collection and analysis Avg 16 shots each, fit, repeat 32 times (~5s) Repeat 1440 times (~2 hr) B E Ω E Ω 0.01s

24 Preliminary systematic checks

25 Results ΔE systematic: Applied ΔE= 1.3 V/cm, measured 1.34 ± 0.32 V/cm, limit during data taking <80 mv/cm ΔB systematic: Masked by field drift up to 400 µg (ΔB/B=2.5 x 10-3 ) over several hours EDM data: 41 hours of data with no cuts 66% duty cycle maintained over 36 hrs; with further automation >90% should be easily achievable EDM (10-26 e cm) Best fit eedm = -1.9 ± e cm

26 The future of PbO Current limitations are now well understood and verified experimentally Improvements since May Better heat shielding, lower blackbody Excitation from ground vibrational level -> 3x increase in count rate Near term improvements (by end of year) Optimize detection filters -> increase count rate by 2-4 Polarization sensitive detection -> reduce background by 2, increase contrast by up to 2 Seed dye laser to match Doppler profile -> increase contrast by up to 4, increase count rate by up to 5 Total increase in sensitivity of Improving upon the Berkeley result is nearly at hand! Focus will shift to ThO beam experiment

27 Acknoledgements Current PbO group: David DeMille (PI), Hunter Smith Former members: Yong Jiang, Sarah Bickman, Amar Vutha